Mrs. Paulgaard Biology 30

Notes & Diagrams

Cell Division, Molecular (DNA) Genetics, Mendelian Genetics,

& Population Genetics

Cells, Chromosomes and DNA The Cell Cycle:

Described in two parts: o Interphase: occupies most of the cells life cycle (90%) and subdivided into three

sections G-1 phase, S phase, and G-2 phase.

Stages of Interphase

Characteristics

Gap 1 Cell growth, protein synthesis, normal cell functions, about 11 hours

S phase (synthesis) DNA replication, up to 7 hours

Gap 2 Cell growth, protein synthesis, 4 hours

o Cell Division: divided into two parts nuclear division (mitosis or meiosis) and

cytokinesis (10%)

TERMS:

Chromatin Strands of genetic material (DNA) that are unraveled into long thin strands (accessible DNA) during interphase. Found during the resting phases of the cell’s life cycle

Chromosome Thick shortened strands of genetic material (DNA) that is inaccessible or packaged. Noticeable just before cell division (condensed)

Chromatid

Replicated, identical chromosomes that are attached at the centromere. Chromatid pairs are found during cellular division (metaphase of mitosis and meiosis)

Homologous Chromosomes

Chromosomes that contain similar genes or DNA sequences but are not identical. One of the pair comes from each parent.

Nucleolus Used in the synthesis of ribosomes (protein synthesis)

Spindle fibers Protein strands that attach to the centromere and pull the chromatids to opposite ends of the cell

Centriole Found in animal cells only. They provide attachment for spindle fibers

Centromere The spot, usually in the middle, on the chromosome where the spindle fibers attach. This spot holds the two sister chromatids together.

Mitosis: Asexual Reproduction (1 Parent Cell)

Nuclear division characterized by chromosome replication and formation of two identical daughter nuclei (2n) using one division.

Division normally occurs in most body or somatic cells (exceptions include muscle and nerve cells and cells in the ovaries and testes)

These cells are used for growth or replacement of dead or damaged cells. Stages of Mitosis

Prophase Nuclear membrane breaks down, spindle fibers begin to form, chromosomes condense

Metaphase Spindle fibers formed and attach to centromeres, chromosomes line up across equatorial plate

Anaphase Chromatids segregate (separate) and move to opposite spindle poles

Telophase Nuclear membrane reforms, chromosomes disappear, cytokinesis occurs

Cytokinesis:

Equal division of the cytoplasm between the two daughter cells.

The parent cell has now split into two new daughter cells, each cell has the same number of chromosomes as the parent cell (this is called the diploid number of chromosomes)

Regulation of cell division:

The purpose of cell division is to replace dead or damaged cells, and for growth and requires a stimulus to divide.

Stimuli include: o Environmental Agents (Toxins/Radiation) o Damage to neighboring cells (bruises, cuts, or burns) o Hormone signals (HGH, thyroxin) o Genes within the cell

Cancer:

Group of disorders that occur when cell division becomes uncontrolled and produces too many immature (young) cells that have too many chromosomes and therefore are nonfunctional.

If the cells continue to divide at faster than normal rates they form an area of dense tissue, or a lump/tumor.

o The malignant tumors are the actual “cancerous” tumors that are composed of nonfunctional cells, and may spread to other areas of the body, called metastasis.

o The benign tumors have functional cells and are therefore classified as noncancerous.

Stem cells:

Cells that can divide over and over again to form the specialized cells, tissues and organs that make up our body.

Totipotent stem cells: o Cells that can have the ability to develop into any cell including extraembryonic

membranes.

Pluripotent stem cell or Embryonic stem cells: o Cells that can form all cells, tissues and organs in the body except the

extraembryonic membranes.

Committed stem cells/ Adult stem cells: o Cells that are unique to the organ and can only develop into more specialized

cells of that same organ. o Example: nerve cells in the brain, or blood cells in the bone marrow

Identical twins: o Produced from one fertilized egg that divides abnormally, in early development usually before

the blastocyst stage, to produce two separate embryos. o The twins are identical in every way. Fraternal twins: o Produced when two separate eggs are ovulated and fertilized by separate sperm cells. They

will each implant separately producing separate placentas. o The twins will not be identical. Meiosis: Sexual Cell Division

Only occurs in the ovaries and testes.

Produce gametes, or sex cells (sperm and egg) that have half the chromosome number.

These cells are called haploid (n) while the parent cell that gives rise to them is still diploid (2n).

o Haploid cells have only one type of each chromosome (23 chromosomes) o Diploid cells have 2 of each type of chromosome (23 pairs or homologous

chromosomes = 46 chromosomes)

Having the identical form and arrangement of genes (but different alleles)

Mitosis involves only one division of the parent cell (somatic cell).

Complete meiosis involves two successive divisions, which result in 4 new haploid cells: o The first division produces 2 haploid cells having double-stranded chromosomes o The second division produces 4 new haploid cells having single-stranded

chromosomes

Regulation of Meiosis:

The purpose of gamete formation is for variation.

Stimuli include: o Environmental agents o Hormone signals (FSH) o Genes within the cell

Stages of Meiosis

Prophase I o Nuclear membrane disappears, chromosomes condense, become visible, homologous chromosomes pair up (synapsis) forming a tetrad, crossing over occurs here.

o Homologous chromosomes are chromosomes that have similar shape, size, and genes

Metaphase I o Homologous chromosomes line up randomly on the equatorial plate, spindle fibers attach to the centromere

Anaphase I o Homologous chromosome pairs move to opposite poles of the cell in a process called segregation.

o The chromatids do not separate at the centromere

Telophase I o Cytokinesis occurs forming two cells with half the number of chromosomes as the parent cell, nuclear membrane forms around the chromosomes

Prophase II o Spindle fibers form, nuclear membrane disappears

Metaphase II o Chromosomes line up at equatorial plate, spindle fibers attach to centromeres

Anaphase II o Spindle fibers pull chromatids apart (breaks the centromere) and chromatids/chromosomes move to opposite poles of the cell

Telophase II o Nuclear membrane reforms around chromosomes, cytokinesis occurs producing two haploid cells from each cell.

Oogenesis: o Production of egg cells (ova/ovum) in the ovary. o Produces 4 cells, 1 larger egg cell (ovum) and 3 smaller cells (called polar bodies) that die Spermatogenesis: o Production of sperm cells in the testes. o Results in the formation of four small sperm cells (from one parent cell).

Meiosis is important because:

It conserves the chromosome number in sexually reproducing species. Without it the number of chromosomes would be doubled every generation.

It continually reshuffles the genetic material (recombination) between generations producing natural variation.

Crossing Over:

This occurs during prophase I of meiosis.

When the homologous chromosomes pair up the chromatids of the different chromosomes in one pair will exchange parts (genes).

The significance of this is it adds more variation to the population by producing individuals with new combinations of characteristics.

New variations will give the population a better chance of surviving by providing adaptations to the new environment.

Sources of Variation:

Mutations

Genetic Recombination (Fertilization)

Crossing Over or Synapsis

Random Assortment

Comparison of mitosis and meiosis

Mitosis Meiosis

o Produces body cells (somatic) o Produces sex cells (gametes, sperm and egg)

o Homologous chromosomes line up independently along the equatorial plate during metaphase

o Homologous chromosomes line up together along the equatorial plate (synapsis) forming four chromatids (called a tetrad) during the metaphase I

o Occurs in all locations of the body (somatic cells)

o Occurs only in the gonads

o One nuclear division per cycle o Two nuclear divisions per cycle

o Chromosome pairs replicate before mitosis o Chromosome pairs replicate before meiosis

o Two identical cells from one parent cell o Four cells from one parent cell

o Diploid cells produces from diploid parent o Haploid cells produces from diploid parent

o Daughter cells are capable of further divisions

o Gametes are not capable of further division

o Genetic content of cells is identical o Genetic content of cells is scrambled (crossing over)

Nondisjuction (chromosomal mutations) Abnormal Meiosis: Non-disjunction

The gametes produced will have an abnormal number of chromosomes

Caused by either: o Pairs of homologous chromosomes do not move apart properly during anaphase I o Sister chromatids fail to separate during anaphase II

If one of these gametes should fertilize a normal gamete the resulting individual will have an extra chromosome (trisomy), or lack a chromosome (monosomy).

The effects are categorized as ‘syndromes’. o Examples:

Down syndrome: 3 copies of chromosomes 21 (trisomy 21) with a total of 47 chromosomes.

Turner syndrome: woman has only one X chromosomes (monosomy X) and therefore has only 45 chromosomes in her body cells.

Klinefelter’s syndrome: man has an extra X chromosome (XXY) and a total of 47 chromosomes.

Chromosomal disorders resulting from non-disjunction can be detected during pregnancy using the fetus’ karyotype.

Karyotype

This is a chart of the pictures of all the chromosomes, arranged in order from longest to shortest, of an organism.

The human karyotype has 4 rows of 23 pairs of chromosomes (46 chromosomes in all) o 44 or 22 pairs are called autosomes o 2 chromosomes or one pair are called sex chromosomes

Strategies of Reproduction:

o Only one measure of its evolutionary success: the proportion of its genes present in future generations and the reproductive adaptations of organisms are many and varied

1. Sexual reproduction

o Involves different sexes of a species producing gametes that unite to produce and embryo that grows into a new individual.

o Fertilization can happen externally, as in fish, or internally, as in birds and mammals. o The embryo can grow internally in a uterus, or externally in an egg. o There are many variations of these strategies.

2. Asexual reproduction

o Involves one member of a species cloning itself. o No gametes are required. o Examples of this include runners in strawberries and poplar trees, and binary fission in

bacteria. Binary fission

o A form of asexual cell reproduction in which the parent organism splits in half to form two new (diploid) individuals

Parthenogenesis o This involves the development of an organism from an unfertilized egg. o Dandelions, some fish and lizards, as well as many insects perform this.

3. Alternation of Generations (Plants) o This involves the alternating between diploid and haploid stages within the life cycle of

sexually reproducing plants. o There are various forms of this process throughout the living world.

o Sporophyte produces, asexually, spores, reproductive cells that can grow into new individuals without fertilization (gametophytes)

o Gametophyte plant produces gametes which must fuse to produce a cell called a zygote, which then develops into a new individual

Genetic Material:

o Composed of DNA, RNA, Genes, and Chromosomes o DNA carries the instructions to put amino acids into sequences that make proteins.

Discovery of DNA:

James Watson and Francis Crick first identified DNA structure in 1953 Structure of DNA

The Watson-Crick model of deoxyribonucleic acid is similar to the shape of a twisted rope ladder.

o DNA is made up of nucleotides which are made up of: Five-carbon sugar (deoxyribose). Phosphate (PO4-) One of four nitrogen bases

adenine [A] ~ Purine

guanine [G] ~ Purine

thymine [T] ~ Pyrimidine

cytosine [C] ~ Pyrimidine

Sugar-phosphate groups are the backbone (rails of the ladder) Rungs are the nitrogen bases bond with each other, called base pairs,

via hydrogen bonds.

Adenine will only bond with Thymine

Guanine will only bond with Cytosine.

These bonds tend to break at temperatures over 70°C and the DNA denatures.

o It has a full twist every ten nucleotides. {Double helix shape} o The two strands of DNA are complimentary because the nitrogen bases that form

the rungs. Genes: o DNA is subdivided into segments called genes. o A gene is composed of many nucleotides. o Each gene codes for a specific protein (one gene-one enzyme hypothesis). o Allele: the variations of a gene. e.g. eye colour.

Types of Genes: Introns: meaningless segments that does not code for no specific protein and appear to

have no function. Exons: parts of the DNA that actually form the gene.

o Structural Genes: these are genes that direct the synthesis of proteins in individual cells.

The proteins are used to build cell structure or other important molecules. Ex. hormones, neurotransmitters, hair.

o Regulator Genes: control the production of repressor proteins which switch off structural genes.

o Oncogenes: are genes that specifically cause cancer. o Transposons: moveable genes that can ‘jump” along the chromosome.

Chromosomes: o Chromosomes (DNA molecule) can carry several hundred to several thousand genes,

depending on the size of the chromosome. o Chromosomes are composed of a long molecule of DNA and proteins that the DNA wraps

around. o The larger the chromosome the longer the DNA molecule and the more base pairs it has. Functions of DNA

Self-Replication Protein-Synthesis: coding for structural proteins and enzymes thereby controlling the

cellular activities of an organism. DNA Replication: (DNA synthesis of the cell cycle ~ Interphase)

o DNA replication is semi-conservative - the daughter strands are made up of one half old strand and one half new strand.

o This occurs in two stages: 1. The DNA “unzips” or “unwinds” between the nitrogen bases, breaking the

hydrogen bonds. 2. These exposed bases attract free floating bases (which come from the food we

eat and are floating around inside the cell cytoplasm) which match up with complimentary nucleotides on DNA strand. DNA polymerase and ligase enzymes catalyze this reaction.

Ligase-are enzymes that glue DNA nucleotides together at the nitrogen bases DNA polymerase- joins the phosphates to the sugars to form the sides of the DNA ladder

Protein Synthesis:

A gene codes for the production of a specific protein by specifying which amino acids to use, in what order, and how many.

This occurs in two sequences: Transcription and Translation Transcription (DNA mRNA Ribosome)

A process of copying the nitrogen base sequence in the DNA and bringing it to the ribosome where translation occurs.

There is a special type of nucleic acid built to perform this function called messenger RNA, or mRNA.

There are three steps in transcription: 1) DNA of a specific gene unzips between the base pairs. 2) mRNA nucleotides attach (base pair) to the exposed nitrogen bases of the DNA molecule. 3) The mRNA nucleotides join together forming a single strand that detaches, leaves the

nucleus, and moves to the ribosome.

Translation (mRNA Ribosome Amino Acids (tRNA) Protein)

This is a process of translating the mRNA nitrogen base sequence into a series of amino acids that will link together to form a protein.

This process involves the use of transfer RNA or tRNA. Translation occurs in five steps: 1) mRNA strand attaches to the ribosome 2) tRNA pick up amino acids (from the food we eat) in the cell 3) tRNA with attached amino acids move to the mRNA. The tRNA anticodons match up and

attach to mRNA codons

Codon: set of three nitrogen bases on the mRNA will code for one amino acid o 20 Amino Acids o 64 Codons = 43 = 60 plus 4 to start (initiator codon) and stop (terminator

codon) transcription

Anticodon: set of three nitrogen bases found on the tRNA 4) amino acids bond together to form a protein 5) mRNA and tRNA break apart with the mRNA returning to the nucleus and tRNA returing to

the cytoplasm to pick up more amino acids.

DNA vs. RNA

DNA RNA

Double Helix Single Helix

Deoxyribose Ribose

Nitrogen bases A, T, C, G Nitrogen bases A, C, G, U (Uracil replacing Thymine)

Found in the nucleus Found in the cytoplasm

DNA can self-replicate under the right conditions

Mutations

A permanent change to the genetic code (nitrogen base sequence) at one point or in large sections.

Caused by mutagenic substances such as ionizing radiation (x-rays, cosmic rays, and UV light), free radicals, viruses, and many other chemicals.

The effect of base changing is that the protein the DNA codes for will be altered leading to different amino acids being transcribed. (substitution mutation)

o Degeneracy: when more than one codon can produce the same amino acid o The new proteins may be harmful, nonfunctional, or beneficial.

Types of DNA Mutations:

Point mutations: a minor mutation where one nucleotide pair replaces another. o Insertions: an extra nucleotide is added into the DNA molecule.

Example: ACGCCA becomes AACGCCA o Deletions: a nucleotide is removed from the DNA molecule

Example: ACGCCA becomes CGCCA o Substitution: one nucleotide is replaced for another in the DNA sequence.

Example: ACGCCA becomes CCGCCA

Frame shift mutation: a point form mutation in which a nucleotide pair is inserted or deleted causing the whole strand to be translated differently.

o Examples include insertion and deletion.

Chain terminating mutation or nonsense mutation: a mutation resulting in a stop signal instead of a normal amino acid.

o This can result in a fragment of the protein being produced instead of the whole protein.

Silent mutations: a mutation which has no effect on the individual. o Many point mutations have no effect on the cell because certain amino acids

have more than one code. Types of DNA

o DNA is found in the nucleus, mitochondria and chloroplasts. o Mitochondrial DNA is inherited only from the mother. It can be compared to determine

ancestry of organisms. Protein Clock Theory:

o A method using differences in types of amino acids of the same protein in different species to determine evolutionary ancestry.

o It states that the greater the difference in types of amino acids used to make the same protein the further in the past the evolutionary ancestor of those organisms existed.

o Example: hemoglobin in fish, amphibians, humans and horses Human Genome project

A worldwide research project to identify all the nitrogen base sequences for all the genes of the human

Biotechnology and Genetic Engineering

Biotechnology is the application of knowledge of DNA to the production of materials for human use.

Genetic Engineering a desired gene can be isolated and millions of copies of it made o Recombinant DNA: Functioning genes have even been transferred into cells or

bacteria, yeasts, plants and animals o Gene Therapy: replacement of defective genes with normal healthy genes

Ex: cystic fibrosis, hemophilia, sickle-cell anemia, immune deficiencies o Agriculture: introduction of genes for resistance to disease, drought, frost,

increased protein production, larger fruit, Bt corn, Canola (Roundup)

DNA Fingerprinting

The DNA sample tested is exposed to restriction enzymes and then the resulting DNA fragments are placed in an electrophoresis gel that separates the segments by size and charge (Bands).

This is then compared with another sample of DNA to see if the two samples are the same.

How recombinant DNA technology is done:

1. The desired gene has to be isolated and cut out of the DNA using a restriction enzyme (endonulease).

2. The isolated gene is inserted into a bacterial plasmid (circular DNA) using a ligase.

This new DNA is now termed recombinant DNA. 3. The plasmid is absorbed by a bacterium, which reproduces asexually to produce

many clones containing the recombinant DNA. 4. The bacterial cells produce the protein coded by the foreign gene. This desired

protein can be isolated and purified from the culture.

Examples:

human growth hormone, human insulin, and interferons, which combat viral infections and may help in fighting cancer, by creating antibodies

Genetics Hereditary characteristics/Genetic Trait:

Characteristic determined by genes carried on chromosomes passed from parents to offspring.

Examples are height, eye color, and the ability to roll your tongue. Acquired characteristics:

Characteristics received from the environment and are not passed on to offspring and do not affect the genes.

Genetics:

The study of the patterns of inheritance as hereditary characteristics or traits passed from parents to offspring.

Gregor Mendel the “Father of Genetics” studied the mechanisms of inheritance in garden peas. (1866)

Gregor Mendel’s Four Laws of Inheritance:

Law of Parental Equivalence: Each inherited characteristic is determined by at least two genes (pair); one from each parent.

Law of Dominance: One gene may mask the effect of another. The gene that is expressed is dominant, while the one that is masked is recessive.

Law of Segregation: During gamete formation (meiosis), each member of the allelic pair separates from the other member to form the genetic constitution of the gamete.

Law of Independent Assortment: During gamete formation, the segregation of the alleles of one allelic pair is independent of the segregation of the alleles of another allelic pair.

Terms:

Allele: The different forms of a gene. (variation on the trait) o More than two alleles can exist for any specific gene but only two of them will be

found within any individual. o Dominant allele = D o Recessive allele = d

Genotype: the specific allelic combination for a certain gene or set of genes.

Phenotype: "the form that is shown" o The outward, physical appearance of a particular trait in an individual.

Homozygous: Having two of the same allele, e.g. DD or dd. o Homozygote: An individual which contains only one allele at the allelic pair

DD is homozygous dominant dd is homozygous recessive Pure lines are homozygous for the gene of interest.

o Purebred: an organism having all homozygous gene pairs.

Heterozygous: Having two different alleles e.g. Dd. o Heterozygote: An individual which contains one of each of the gene pair

Dd is a heterozygote. o Hybrid: - an organism having at least one heterozygous gene pair.

Monohybrid: - an organism having only one heterozygous gene pair. Dihybrid: - an organism having two heterozygous genes pairs.

Example: Using Mendel’s peas

Yellow seeds are dominant to green seeds so the alleles for seed color are: o Y=yellow and y=green.

Genotypes for seed color are: o h. dom = YY hetero = Yy and h.reces = yy. o The dominant allele is always written before the recessive allele of the same

characteristic in any genotype.

Phenotypes (what the seeds look like) are: o YY and Yy are yellow and yy is green

Punnett Squares:

Tables drawn to predict the possible offspring from a cross between two individuals.

Helps predict the outcome of a genetic cross

When doing crosses always use the following problem solving method. 1) State what the alleles mean, assign letters to the dominant and recessive alleles. 2) Identify the parent cross in words and after in genotype symbols. 3) Identify the gametes from each parent and set up the punnett square. 4) Interpret the genotypes and phenotypes from the punnett square and answer the problem.

Single Trait Crosses (Monohybrid Crosses):

A cross between two individuals with respect to a single trait. Example:

Alleles: o R= red r= white

P1 (parental generation):

Purebred (homozygous dominant) red X purebred white (homozygous recessive) o RR X rr (Genotypes)

Gametes (alleles): R r F1 (first offspring generation):

r r

R Rr Rr

R Rr Rr

Genotype (all heterozygous Rr) and phenotypes all red F2 (second offspring generation):

R r

R RR Rr

r Rr rr

Genotypes (1:2:1 or ¼ : ½ : ¼ or 25%:50%:25% RR:Rr:rr)

Phenotypes ¾ red (75%) and ¼ white (25%) Example: Suppose in pea plants tall is dominant to short for the height of the plant. The possible alleles in the gametes can only be tall (T) or short (t). The cross or punnett square is set up as follows:

Alleles: o T=tall t=short

P1 (parental generation):

heterozygous tall X heterozygous tall o Tt X Tt

F1 (first offspring generation):

T t

T TT Tt

t Tt tt

Genotypes (1:2:1 or ¼ : ½ : ¼ or 25%:50%:25% TT:Tt:tt)

Phenotypes ¾ Tall (75%) and ¼ short (25%) F2 (second offspring generation):

T T

T TT TT

t Tt Tt

Genotypes (2:2 or ½ : ½ or 50%:50% TT:Tt)

Phenotypes all tall (100%)

Test Cross

Any cross with a homozygous recessive can indicate what the genotype of the parents are since it is the only observable genotype.

Cross the organism with one of a homozygous recessive individual and then observe the offspring

Example: Determine whether a red-flowered pea plant is homozygous or heterozygous?

Alleles: o R = red r = white

P1 (parental generation):

homozygous red flowered X white-flowered homozygous o RR? X rr

F1 (first offspring generation):

r r

R Rr Rr

R Rr Rr

Genotype (Rr)

Phenotypes all red (100%) If no offspring showing the recessive phenotype are produced, the unknown parent must be homozygous. OR P1 (parental generation):

heterozygous red flowered X white-flowered homozygous o Rr? X rr

F1 (first offspring generation):

r r

R Rr Rr

r rr rr

Genotypes (1:1 or ½ : ½ or 50%:50% Rr:rr)

Phenotypes ½ red (50%) and ½ white (50%) If any offspring showing the recessive phenotype are produced, the unknown parent must be heterozygous.

Variations of the Single Trait Cross: 1. Incomplete Dominance:

o This occurs when neither allele for a characteristic is dominant (both alleles are equal).

o The heterozygous individual expresses neither of the phenotypes of the two alleles but expresses a new intermediate phenotype.

Example: Flower color of snapdragons is incompletely dominant with red, white and pink in the hybrid individual.

o Alleles: Red=R, white=W, pink=RW.

P1 (parental generation): o Red snapdragon X White snapdragon

RR X WW F1 (first offspring generation):

R R

W RW RW

W RW RW

Genotype (RW)

Phenotypes all pink (100%)

F2 (second offspring generation):

R W

R RR RW

W RW WW

Genotypes (1:2:1 or ¼ : ½ : ¼ or 25%:50%:25% RR:RW:WW)

Phenotypes red (25%), pink (50%), white (25%)

2. Codominance: o This occurs when both alleles are dominant (again, both alleles are equal). o In this case both alleles get expressed in the heterozygous individual producing

mixed phenotype. Example: Coat color is shorthorn cattle: Red=R, White = W, Roan = RW this is a mixture of both red and white hairs in the coat giving the animal a reddish grey blotchy coat.

o Alleles: Red=R, white=W, roan=RW. P1 (parental generation):

o Red shorthorn X White shorthorn

RR X WW F1 (first offspring generation):

R R

W RW RW

W RW RW

Genotype (RW)

Phenotypes all roan (100%)

F2 (second offspring generation):

R W

R RR RW

W RW WW

Genotypes (1:2:1 or ¼ : ½ : ¼ or 25%:50%:25% RR:RW:WW)

Phenotypes red (25%), roan (50%), white (25%)

Multiple Alleles:

This occurs when there are more than two alleles for a characteristic.

Consequently there can be more than two phenotypes.

The most common example of multiple alleles is blood type in humans. Blood type in humans:

A and B alleles are codominant (IA = IB)

O allele is recessive to both A and B (IA = IB >i)

The phenotypes and genotypes are: o Type A blood IA IA or IA i o Type B blood IB IB or IB i o Type AB blood is only IA IB genotype o Type O blood is only ii genotype.

Example: A man that is Type A heterozygous crosses with a woman who is Type B heterozygous.

o Alleles: IA =type A, IB =type B, ii=type O, A and B are codominant.

P1 (parental generation):

o Type A heterozygous X Type B heterozygous

IAi X IBi F1 (first offspring generation):

IB i

IA IA IB IA i

i IB i ii

Genotypes 1:1:1:1 25% for each of IAi, IB i, IA IB, and ii

Phenotypes 1:1:1:1 25% for each of A, B, AB, and O

Note: Another form of notation for blood type uses the capital I with a superscript A = A allele, I with a B = B allele, i = O allele

Two Trait Crosses (Dihybrid Crosses):

This type of cross involves examining the inheritance of two characteristics at the same time. Example where both parents are heterozygous for both characteristics (called a dihybrid)

Consequently there will be more gametes with different combinations of alleles that could be used for fertilization.

Traits are found on separate chromosomes. Example: plant height and seed color.

o Alleles: plant height: tall= T and short= t, and seed color: yellow= Y and green= y P1 (parental generation):

o Tall yellow seed plant X tall yellow seed plant (both parents are heterozygous)

TtYy X TtYy F1 (first offspring generation):

TY Ty tY ty

TY TTYY TTYy TtYY TtYy

Ty TTYy TTyy TtYy Ttyy

tY TtYY TtYy ttYY ttYy

ty TtYy Ttyy ttYy ttyy

Genotype ratio: not done when chart is this big

Phenotype ratio: always 9:3:3:1 o 9/16 (both dominant characteristics) tall and yellow seeds o 3/16 (dominant, recessive) tall and green seeds o 3/16 (recessive, dominant) short and yellow seeds o 1/16 (recessive, recessive) short and green seeds

Variations of the Two Trait Cross: 1. Epistatic Interaction:

o This involves genes that prevent the expression of other genes. o Coat color in dogs is an example.

Example: Coat color in dogs

o Alleles: B=black, b=brown, a separate gene on a separate chromosome also

influences coat color, W=prevents color formation & results in white, w=allows color formation.

P1 (parental generation): o White dog X Black dog

WwBb X wwBb F1 (first offspring generation):

wB wb

WB WwBB WwBb

wB wwBB wwBb

Wb WwBb Wwbb

wb wwBb wwbb

Phenotypes : 4/8 White, 3/8 black, 1/8 brown

2. Complementary Interaction: o This occurs when two different genotypes interact to produce a phenotype that

neither is capable of producing by itself (like incomplete dominance).

Example: combs of chickens

Alleles: rose comb=R, pea comb=P (on a different chromosome), R and P alleles are both present = walnut comb, & the absence of both R and P (only recessive, r and p, homozygous for both r and p) produces single comb.

P1 (parental generation): o rose comb X pea comb (both parents homozygous for rose and pea)

RRpp X rrPP F1 (first offspring generation):

rP

Rp RrPp

Phenotypes : Produces 100% RrPp which is walnut comb F2 (second offspring generation):

RP Rp rP rp

RP RRPP RRPp RrPP RrPp

Rp RRPp RRpp RrPp Rrpp

rP RrPP RrPp rrPP rrPp

rp RrPp Rrpp rrPp rrpp

Phenotypes: o 9/16 walnut (RRPP, RRPp, RrPP, or RrPp) o 3/16 rose (RRpp or Rrpp) o 3/16 pea (rrPP or rrPp) o 1/16 single (rrpp)

Ex: A male who is heterozygous for both height and blood type A is crossed with a short woman

who is heterozygous for type B blood. What is the probability of producing a short son with AB

blood? What would be the probability of producing a short daughter with AB blood?

T (tall) > t (short) and IA (A) = IB (B) > i (O)

Recombinant genes

The same genes are found on the same chromosome in all people and are called linked genes.

By examining the results of crosses of linked genes we can determine the sequence the genes are in on a chromosome.

This sequence is called a chromosome map. Example 1: Two-trait cross (no crossing over) on separate chromosomes.

o Alleles: Y=yellow, y=green, R=round seed, r=wrinkled seed P1 (parental generation):

o Yellow round X Yellow round (both are heterozygous)

YyRr X YyRr F1 (first offspring generation): Each alleles is carried on a separate chromosome

YR Yr yR yr

YR YYRR YYRr YyRR YyRr

Yr YYRr YYrr YyRr Yyrr

yR YyRR YyRr yyRR yyRr

yr yyRr yyrr yyRr yyrr

Phenotypes : 9/16 Yellow round, 3/16 Yellow wrinkled, 3/16 green round, 1/16 green wrinkled

Example 2: Two-trait cross with linked genes (no crossing over) o Alleles: Y=yellow, y=green, R=round seed, r=wrinkled seed

Alleles Y and R are on one chromosome of the pair and y and r are on the other chromosome of the pair.

P1 (parental generation): o Yellow round X Yellow round (both are heterozygous)

YyRr X YyRr F1 (first offspring generation): Two chromosomes that carry the 4 different alleles

YR yr

YR YYRR YyRr

yr YyRr yyrr

Phenotypes: ¾ yellow round, ¼ green wrinkled This illustrates that each alleles could not have been on a separate chromosome otherwise we would see the standard 9:3:3:1 ratio as in example one.

Example 3: Two-trait cross with linked genes and crossing over. o Alleles: Y=yellow, y=green, R=round seed, r=wrinkled seed

One of the parents’ the homologous chromosomes switch genes during gamete formation (metaphase I of meiosis) resulting in a different combination in the gametes.

P1 (parental generation): o Yellow round X Yellow round (both are still heterozygous)

YyRr X YyRr F1 (first offspring generation): From one parent: YR and yr, but from the other: Yr and yR

YR yr

Yr YYRr Yyrr

yR YyRR yyRr

Phenotypes: ½ yellow round, ¼ yellow wrinkled, ¼ green round Notice that there are no green wrinkled. The unexpected phenotypes produced from this cross, yellow wrinkled and green round, (as compared to example two of just linked genes) are called recombinants because they formed as a result of a recombination of genes, by crossing over, during gamete formation. Chromosome (Gene) Mapping:

The location of a specific gene on a chromosome is called its locus.

Crossing over will occur more often between two genes that are at opposite ends of the same chromosome than genes that are right next to each other.

The number of recombinant individuals produced in a cross, divided by the total offspring produced by the cross is described as the crossover frequency for these genes.

% recombination = number of recombinants X 100 Total offspring

The crossover frequency can be translated directly into a map distance that measures how far the genes are apart from each other.

The higher the crossover frequency the farther the genes are apart from each other on the chromosome.

o A frequency of 5% means a map distance of 5 map units. o A frequency of 10.5% means a map distance of 10.5 map units.

From a table of data that lists crossover frequencies between several genes we can map the genes in a sequence on the chromosome.

Example 1:

Genes W X Y Z

W 5 7 8

X 5 2 3

Y 7 2 1

Z 8 3 1

The sequence would map out as:

W—5—X—2—Y—1—Z

Example 2:

Genes A B C

A 10 5

B 10 15

C 5 15

The sequence would map out as: Example 3: Drosophila, the following data was obtained from genetic crosses:

13% recombination between bar eye and garnet eye

7% recombination between garnet eye and scalloped wings

6% recombination between scalloped wings and bar eye

Genes Bar Garnet Scalloped

Bar 13 6

Garnet 13 7

Scalloped 6 7

The sequence would map out as:

Chromosome Theory: combines Mendel’s Laws with discoveries in cytology over the years. 1. Genes control all traits and are carried on chromosomes 2. Chromosomes undergo segregation (chromosomes separate)during meiosis 3. Chromosomes assort independently (chromosomes line up independently of each

other)during meiosis 4. Each chromosome contains many different genes.

The genes on one chromosome are all linked together

Sex is determined by two chromosomes Thomas Hunt Morgan:

Added evidence from fruit flies to support the chromosome theory of inheritance. o Autosomes o Sex Chromosomes o Sex Linked Crosses

Autosomes:

22 pairs of chromosomes (44 in all) that determine most of our characteristics except sex.

Genes that are carried on these chromosomes are called autosomal o Autosomal dominant (trait named after the dominant condition) o Autosomal recessive (trait named after the recessive condition) o Autosomal codominant o Autosomal incomplete dominant o These are called the “modes of inheritance”

Sex Chromosomes: first identified by Thomas Morgan

These are the one pair of chromosomes that determine if we will be male or female.

Males receive and X and a Y chromosome, females receive two X chromosomes.

Sex Linked Crosses:

X chromosome also carries other genes that they Y chromosome did not carry o Ex. blood clotting factors (hemophilia) and color vision.

Dominant alleles = ‘normal’ development of that characteristic

Recessive alleles = results in incomplete development, or improper functioning, of that characteristic.

o Males would always express the gene he receives since he only has one X. o Females would only express the recessive gene if they are homozygous

recessive.

As a result these ‘sex linked genes’ or ‘sex linked disorders’ are seen more in males than females, but can occur in females.

Remember: you must show the sex chromosomes with the allele carried when solving sex-linkage

Sex linked crosses: the alleles are expressed as superscripts only on the X chromosome.

Skips a generation…. Example: a colorblind man marries a normal vision woman with no history of colorblindness.

o Alleles: XY= male XX = female normal vision = C colorblind=c P1 (parental generation):

o Colorblind man X normal women

XcY X XCXC F1 (first offspring generation):

Xc Y

XC XCXc XCY

XC XCXc XCY

Phenotypes: 50% male normal & 50% female carrier (they are heterozygous for vision but are still normal)

Ex: A normal vision man meets and marries a normal vision woman whose material grandfather

was colourblind. When they have a child, what is the possibility that they will have a colourblind

child? What is the possibility of having a son who is colourblind?

XN=Normal vision > Xn=Colour vision

Pedigree Charts:

Each generation is numbered using Roman numerals o Oldest generation always number I.

Each individual within each generation is numbered with an Arabic numeral (each individual is known by the combination of the generation and the individual numbers)

o E.g., III-4.

The gender and genotype of the individuals are indicated by the following symbols: o O=female, □ =male,

Totally shaded in they express the disorder Half shaded means a known heterozygote for an autosomal recessive

disorder Dot in a circle is a known carrier of a X-linked (sex linked) recessive

disorder.

A carrier is an individual with a normal phenotype, but is heterozygous.

Pedigree diagrams are drawn to illustrate the inheritance of a particular trait over several generations within a family. The following is a key to how the pedigrees are coded:

I II III

Autosomal Dominant Inheritance Autosomal dominant conditions result from an individual carrying one changed gene. Clues that geneticists use when looking at pedigrees to determine autosomal dominant inheritance include the following facts:

1. Autosomal dominant conditions are seen in every generation (vertical pattern). 2. Males and females have the condition with equal frequency and severity. 3. Unaffected individuals do not have children with the condition. 4. Each child of an affected individual has a 50% chance of being affected, regardless of

sex or birth order. 5. Homozygotes for autosomal dominant conditions (individuals with two changed genes)

have a more severe form of the disease.

I II III

Autosomal Recessive Inheritance Autosomal recessive inheritance is seen in conditions that are due to having two changed genes.. Characteristics of autosomal recessive traits include:

1. The condition typically appears in one generation (siblings) and nothing in their parents or offspring ("horizontal inheritance").

2. Males and females are equally affected. 3. Both parents are asymptomatic heterozygotes (carriers) meaning they only have one

changed gene. 4. Two carrier parents have a 1 in 4 (or 25%) chance of having an affected child. 5. Each unaffected full sibling of an affected individual has a 2/3 chance of being a carrier. 6. Offspring of an affected individual will be a carrier and therefore be unaffected unless the

other parent is a carrier or is affected with the same condition.

I II III

X-Linked Dominant Inheritance There are very few X-linked dominant traits. Characteristics of this mode of inheritance include:

1. Affected males transmit the trait to all of their daughters and none of their sons. 2. Affected females transmit the trait to half of their sons and half of their daughters. 3. There are usually twice as many affected females as affected males but affected females

often express the condition to a milder degree.

I II III

X-linked Recessive Inheritance X-linked dwarfing conditions are rare. Criteria for this mode of inheritance include:

1. Males are almost exclusively affected. 2. No father to son transmission occurs but all daughters of affected fathers will be carriers. 3. Depending on the condition, examination of a carrier female may reveal some mild

manifestation. 4. Carrier females have a 50% or 1 in 2 chance of having an affected son and a 50% or 1 in

2 chance of having a carrier daughter. 5. The first affected son in a family may inherit the changed gene from a carrier mother or

may be the result of a new genetic change.

I II III

I II III

I II III

Change in Populations and Communities Species:

Individuals that can reproduce to produce fertile offspring Populations:

all the members of a species that occupy a particular area at the same time

E.g. wolves in Jasper Population Genetics:

genes tend to stay in the same population for generation after generation because individuals within that area will breed with one another than with other populations of the same species

Gene Pool is total sum of all the alleles for a characteristic in a population at one time. o Gene/Allele Frequency: numbers of a specific allele out of the total of that gene

(both alleles) in the population. Hardy-Weinberg Principle

If a population has a stable gene pool and gene frequencies (not evolving) over generations if all other factors remain constant

Equilibrium will maintain a population’s gene frequencies if 5 conditions are met: o Closed population (no immigration or emigration can occur) o Random mating (no mating preferences) o No selection pressure (all alleles are equal & have the same reproductive

success) o No mutations o Large population

If these factors are not constant the frequency of the allele in the population will change.

Mathematical Expression: o Allele Frequencies:

p + q = 1 p = dominant allele frequency (A) q = recessive allele frequency (a)

o Genotype Frequencies:

p2 + 2pq + q2 = 1 p2 = Homozygous Dominant Genotype Frequency (AA) 2pq = Heterozygous Genotype Frequency (Aa) q2 = Homozygous Recessive Genotype Frequency (aa) All three terms add up to 100% of the population so the equation always equals 1 (100%). Equilibrium: the values for these three terms stay the same over a period of time.

Ex: Black hair is dominant to blonde hair. If 80 individuals out of a population of 1000

are blonde, then what are the allele (gene) frequencies? How many out of the 1000 are

heterozygous?

Non-Equilibrium: the values change over a period of time (micro-evolutionary change). Environmental Changes: Populations have three options when the surrounding environment (habitat) changes:

1. Habitat Tracking: (population’s gene pool does not change) they must move to another area similar to the habitat they have genes/traits for.

2. Extinction: (population’s gene pool does not change) they not have traits that allow them to survive in the new habitat and consequently not reproduce as much as possibly other organisms. (natural selection)

3. Micro-Evolution: (population’s gene pool does change) new genes can enter the population giving the species a new trait that might allow some members of the species to survive in that changing environment.

Does not directly cause speciation (a new species formed).

if the population does not demonstrate Hardy-Weinberg equilibrium (i.e. its gene frequencies are not stable) it is in evolutionary change

Conditions that lead to Micro-evolution:

Genetic Drift: small populations result in the frequencies changing as a result of chance. Sampling Error ~ unlikely representation of parent population E.g. flipping a coin 1000 times compared with flipping a coin 10 times

o Founder Effect: The population phenotypes reflect the initial ‘founding’ population.

o Population Bottleneck:

o Random events may bring death to large portion of the population thereby creating a small population.

Mutation: creating new alleles that would alter the frequencies the gene pool. o One gene changes into another and therefore alters gene frequencies in the

population. o chromosome mutation - results from non-disjunction, chromosome

breakage or translocation o gene mutation - changes in the nucleotides (nitrogen base sequence) of a

DNA molecule

Gene Flow: gene pools of most populations of the same species exchange genes. Gaining/Losing Alleles

Migration: new members entering or leaving the population.

Selective Mating: preference for a specific phenotype (may have a selective advantage) then those alleles will occur more frequently in the next generation. non-random mating, inbreeding

Natural Selection: any agent (viruses, predation, parasites, limits on light availability etc) that will kill an individual based on its phenotype.

Populations Interacting within the Same Community: Populations:

Members of the same species in a defined area at a defined time

E.g. wolves in Jasper Community:

Many populations living in the same area and how they interact with each other.

E.g. wolves, deer, spruce, and bees in Jasper Ecosystems:

Non-living (abiotic) factors interacting with living (biotic) factors. o Biotic: the living factors in the environment, other organisms o Abiotic: the nonliving factors in the environment, wind, temperature, humidity,

precipitation

E.g. wolves, deer, spruce, bees, and river in Jasper Habitat:

The environment in which an organism survives.

Limited by climate, water, soil conditions, and vegetation.

Geographic Range: o The total area, extent of locations of habitat, where an organism may live

naturally.

Ecological Niche: o An organism’s profession, role, trophic level or feeding level o It is the total environment and way of life of all the members of a particular

species in the ecosystem o Involves factors like feeding habits, number of offspring per birth, interspecies

(different species) relationships, effect on soil, etc. o E.g. producer/consumer/decomposer, predator, prey, parasite.

Population Interactions:

Cooperative: relations that occur when two or more species live closely together (coexist) over a long period of time.

o Species that do coexist for a period of time in proximity to each other have one or more different factors as part of their niches.

o The relationship may improve the chances of survival for one or both species, or harm one of the species

Detritivory: occurs when one organism consume the dead organic remains of another organism (detritus)

o not a symbiotic relationship

Symbiotic relations (symbiosis) are cooperative

Relationship Definition Interaction Symbol

Commensalism Two organisms of different species that live together and share food, shelter, support.

The commensalist benefits The host is not harmed

(+,0)

Mutualism Two organisms of different species that coexist and benefit from each other

Mutualist benefits Other mutualist benefits

(+,+)

Parasitism When one species (parasite) lives on or in another (host) using the host as a food source or other purposes

Parasite benefits Host harmed Or sometimes not harmed

(+,-)

(+,0)

Competitive: relations that occur when two or more species live closely together (coexist) over a short period of time.

Gause’s competitive exclusion principle: states that two species can not occupy the same niche at the same time without one eliminating the other

o Interspecific competition: different species compete for a limited resource (food).

Reduce or limit the size of a population

Select those members that have the best traits for survival in each species (natural selection).

o Intraspecific competition: members of the same population compete for a limited resource (food, shelter, and mates).

Reduce population size

Select those members of the population that have the best traits for survival (natural selection)

Predation: predator is an organism that hunts and kills another organism called the prey o Predator will cause the prey population to decline, but it is not in its best interest

to kill off all the prey.

Small populations of prey will cause predator populations to migrate or get weak and become more susceptible to disease

o Prey have also evolved various defense mechanisms to predation:

Mimicry: involves developing a similar color pattern, shape, or behavior that has provided another organism with some survival advantage.

Protective Coloration: includes the ability of a prey to blend into its environment by camouflaging itself

Warning Coloration: tell other organisms not to touch them because they are dangerous.

Trickery: using loud noises, changing body size, expelling body parts, pretending to be injured, to distract or frighten the predator.

Freeze Response: prey immediately stops so as not to draw attention. This is effective if the prey has good camouflage

Fight Response: works well against a predator that is not well equipped to fight itself (cheetah), but is often a last resort often resulting is damage to the prey.

Flight Response: prey running from the predator

Group Behaviors:

Chemical Defenses: Growth and Regulation of Populations: Population Size and Density:

Four primary factors that influence the size of a population: o Natality: the birth rate of a population o Mortality: the death rate of a population o Immigration: the movement of new individuals into a population from another

location o Emigration: the movement of members of a population out of the population to a

new location

Closed populations: A population that does not allow immigration or emigration

Open population: A population that allows all four of the primary factors.

Major equations commonly used in population calculations: 1. Population Size: (N)

Change in Population Size ( N) = Nfinal – NInital

Change in Population Size ( N) = (natality + immigration) - (mortality + emigration)

Ex:

N2012=582 deer N= Natality=121 deer/year Mortality=84 deer/year Immigration=56 deer/year Emigration=98 deer/year

N2013=? Ex: N2011=891 rabbits N(2012 to 2014)= N2012=1244 rabbits N2013=1984 rabbits N2014=2563 rabbits

N(2011 to 2013)= 2. Population Density: refers to the number of organisms per unit area (or per unit volume):

Density (Dp) = numbers Dp = N

area (length x width) A

Rate of Change in Density: A negative value for rate of density change means the population is declining while a positive value means the population is increasing

Rate of change in density = change in density R = D

change in time t

Ex: N2014=2563 rabbits N2011=891 rabbits A=15Ha

Dp= _N_ = Dp= _N_ = A A R = D t

3. Growth Rate

Rate = N t

N2011=891 rabbits GR = ___N_ N2013=1984 rabbits t N= t= Per Captia Growth Rate (cgr):

(natality + immigration) - (mortality + emmigration) or cgr = N initial population size N

N2012=582 deer cgr = N N2013=567 deer N Population Growth Rate:

Percent growth rate = cgr x 100% t %GR= = N X 100 N t Compound Growth: exponential growth formula:

NF = NI x (1+cgr)t NF=? deer NF= ? rabbits t=5 years t=5 years cgr= -0.03 N2011=891 rabbits NI= 582 deer N2012=1244 rabbits

Regulation of Population Size Factors Affecting Growth of Populations

o Environmental Resistance: The combination of abiotic factors and biotic factors suppresses the growth of a population

o Density-Independent Factors: (abiotic factors) The occurrence and severity of these factors are unrelated to population

size e.g. weather, climate

o Density-Dependent Factors: (biotic factors) These factors are intensified as the population increases in size

Carrying capacity: the number of individuals of a particular population that the environment can support under a particular set of conditions.

Biotic Potential of Populations: fastest possible rate of population increase

The maximum number of offspring that can be produced by a species under ideal conditions, or the capacity of populations for exponential growth.

Factors which affect biotic potential of a population include: (greater biotic potential)

sexual maturity age - earlier sexual maturation gender ratio - more females length of gestation – the shorter the time carrying offspring estrous cycles - shorter the time between cycles of sexual

receptivity length of reproductive life – longer life mate availability - more readily available mates are in a

population litter or clutch size - larger the litter or clutch size fecundity - "average number of offspring produced per

female"

Population Growth Curves Four phases in this type of growth pattern:

1) Lag phase: initial slow growth o Occurs when the population or organism is adjusting to the new habitat, finding food,

water, mates, shelter. 2) Growth phase: time of rapid (exponential) growth.

o The population more than enough resources to support the rapid growth and there is little environmental resistance.

3) Plateau or stationary phase. period of leveling off of the growth. o During this time environmental resistance slows the growth rate. o In many populations the environmental resistance falls behind the population size

and the population overshoots the carrying capacity. 4) Death phase: period when the population declines.

o Small amount if it has not surpasses the carrying capacity by much and done little damage to the environment or produced small amounts of disease

o A lot due to massive starvation, disease, migration as a result of damage to the environment, lack or food or mates, etc. by the overpopulation.

Types of Growth Curves:

J-Shaped Growth Curves: Closed Population Exponential Population Growth o Unlimited population increase under ideal conditions of unlimited resources

(space, resources, mates, etc.) when the full biotic potential is reached. o Never happens in nature since it occurs in a closed population. o Examples of organisms that may initially exhibit exponential growth include

bacteria and yeast o J shaped growth curves are named after the steep growth phase which will end

in the death phase due to a lack of food or disease.

S-Shaped Growth Curves: Open Population Logistic Growth o Population growth is limited by environmental resistance (resource limitation,

climate, competition, disease and predation) natural populations o The carrying capacity is the maximum stable population size that the

environment can support for a long period of time (biotic potential). o An equilibrium is reached near the carrying capacity of the environment

Population Growth Strategies: Reproductive Strategies o These include the strategies, behaviors, and adaptations members of a population use to

ensure survival of their offspring and growth of the population. o There are two extremes in population growth.

K strategists: Population stabilizes near the carrying capacity of their environment (K)

o Live in stable and predictable habitats. o Slow breeding populations that are able to stabilize at a carrying capacity. o Characteristics:

o Reach a mature age (live longer) o Larger body sizes o Longer parental care of offspring o Longer gestation periods o Smaller litter sizes o Later ages of reproduction

o Examples include elephant, whales, and humans r-strategists: Great reproductive potential (high rate of reproduction = r) that causes them to overshoot the carrying capacity

o Live in an unpredictable rapidly changing habitat. o Fast growing population with a rapid breeding rate (experience periods of exponential

growth) o The populations tend follow a crash/death phase after they overshoot the carrying

capacity. o Characteristics:

o Low maturity age o Shot life span o Small body sizes o Require little or no parental care o Produce many offspring during each breeding o Short gestation periods o Reproduce early and often.

o Examples include fish, flies, mice, and turtles.

Chaos Theory: Long-term predictions may be impossible since randomness is a basic characteristic of

many complex systems. o Population growth is difficult to predict.

However, these very complex phenomena usually share a number of features: 1. Outcomes of processes in a complex system are extremely sensitive to small

differences in the conditions that were present when the process began o The number of factors, both biotic and abiotic, that could influence the

population the overall growth rate are often very large. 2. Once a process is underway, the relationships among the interacting parts of the

phenomena can change as a result of the interactions themselves o The number of interactions between individuals in a population and

between different populations in a community is also difficult to identify. 3. Two systems that appear similar at the start may end up being very different, but

how the two will differ is unpredictable Chaos Theory and Population Growth:

Chaos can account for the ability of these complex systems to respond with flexibility (and unpredictability) to changes in the environment

Change in Communities: Succession

Communities tend to undergo some predictable changes over time called succession Succession:

The sequence of identifiable ecological stages or communities occurring over time in progress of bare rock to climax community

Primary Succession:

Initial colonization of a barren habitat that never supported life by pioneer species. Soil is produced during this stage. e.g. Lichen and mosses growing on rocks.

Succession Stage Populations Abiotic Factors

Pioneer Pioneer plants move into a new environment that normally does not support life. Algae, lichens, and moss.

lots of sun no soil poor water conditions

Seral Shrubs

Seral Deciduous trees - aspen

Climax (balanced)

Complex food webs Pine trees

least amount of sun fertile soil (high biomass & decomposers) good water conditions

After a long time of this existence, enough soil, water and organic material are added to the soil to make it more accessible to other plants (seral communities/stages) which then begin to grow (by windblown seeds, or other methods). Secondary succession:

The gradual changes that reclaim land or water that once supported life. Involves the rebuilding of a certain area that may have at one time supported a well-

developed and stable community. Implies that good soil already exists in the damaged area.