biology chapter 11 introduction to genetics: mendel and meiosis
TRANSCRIPT
IQ #1
1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?
2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?
3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?
Section 11-4: Meiosis
I. MEIOSISA. Meiosis= process of
_________________________ in which the number of chromosomes per cell is cut in 1/2 and the homologous chromosomes that exist in a diploid cell are separated. (and produce haploid cells)
B. Purpose=
Reduction Division
Form gametes (egg and sperm)
II. DIPLOID AND HAPLOID CHROMOSOME NUMBER
A. During ________________ the genetic material from one parent combines with genetic material from another
Example: A fruit fly has 8 chromosomesA set of 4 came from the female flyA set of 4 came from the male fly
B. The two sets of chromosomes are said to be
fertilization
homologous = a female chromosome has a corresponding male chromosome.
C. =contain both sets of homologous chromosomes
D. = contain 1 set only
Male gamete
Female gamete
Diploid (2n)
Haploid (n)
Sperm (n) = 23 chromosomes
Egg (n) = 23 chromosomes
Question: If we start with a diploid cell, how do we get an organism that produces haploid gametes?
Answer: Example: what if:
46
44
8
44
8
16
8
23 2323
46
92
46
Meiosis (aka: reduction division)1 replication; 2 divisions
23
Human Fruit fly
Duplicatedchromosomes
Duplicated
chromosomes
III. PROCESS OF MEIOSIS (DIVIDED INTO 2 STAGES: MEIOSIS I & II
INTERPHASE: growth, DNA synthesis, protein production, organelle production
A. Meiosis I 1. homologous chromosomes pair up (Form tetrads)
2. nucleoli disappear 3. nucleus disappears 4. crossing-over occurs:
portions of chromatids exchange genetic material
2n (diagram 277)
prophase I
Crossing-Over
Go to Section:
Crossing Over: exchange of genetic material between homologous chromosomes
2. spindles attach to chromosomes independent assortment occurs
1. homologous pairs (tetrads) line up at the equator
metaphase I
anaphase I
Key point: homologous pairs separate, cell now haploid
1. spindles pull the homologous chromosomes toward opposite ends of the cell
Telophase I
2. cell begins to separate into two new haploid cells
3. 2 haploid daughter cells
1. Nuclear membranes reform
n n
Interphase I Prophase I Metaphase I Anaphase I
Cells undergo a round of DNA replication, forming duplicate Chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Section 11-4
Figure 11-15 Meiosis
Go to Section:
Meiosis I
Interphase I Prophase I Metaphase I Anaphase I
Cells undergo a round of DNA replication, forming duplicate Chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Section 11-4
Figure 11-15 Meiosis
Go to Section:
Meiosis I
Interphase I Prophase I Metaphase I Anaphase I
Cells undergo a round of DNA replication, forming duplicate Chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Section 11-4
Figure 11-15 Meiosis
Go to Section:
Meiosis I
Interphase I Prophase I Metaphase I Anaphase I
Cells undergo a round of DNA replication, forming duplicate Chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Section 11-4
Figure 11-15 Meiosis
Go to Section:
Meiosis I
B. Meiosis II (similar process as mitosis; no replication)
n
n
n
n
***RESULT: 4 haploid daughters that are genetically different!!
Prophase II
Metaphase II
Anaphase II
Telophase II/Cytokinesis
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Figure 11-17 Meiosis II
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase IIAnaphase II Telophase IIThe
chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II
Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Figure 11-17 Meiosis II
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase IITelophase IIThe
chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Go to Section:
Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II Metaphase II Anaphase IITelophase IIThe
chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Section 11-4
Figure 11-17 Meiosis II
Go to Section:
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meiosis.htmlMeiosis II
IV. GAMETE FORMATION (refer to page 278)A. Males1. 2. male gametes produced by a process called _________________ B. Females1. 4 haploid cells are produced but only 1-haploid cell is a 3-produce 2. female gametes produced by a process called _______________
The 4 haploid cells (gametes) = sperm
spermatogenesis
viable egg polar bodies caused by uneven cytoplasmic division
oogenesis
(a) In the male, all four haploid products of meiosis are retained and differentiate into sperm. (b) In the female, both meiotic divisions are asymmetric, forming one large egg cell and three (in some cases, only two) small cells called polar bodies that do not give rise to functional gametes. Although not indicated here, the mature egg cell has usually grown much larger than the oocyte from which it arose.
V. COMPARING MITOSIS AND MEIOSIS A. Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells. http://biologyinmotion.com/cell_division/
Mitosis Meiosis
Number of daughter cells
Type of cells produced
Number of divisions
Number of replications
Purpose of division
2 diploid cells
1
1
Growth, replacement, repair, asexual reproduction
gametes
2
1
4 haploid cells
Sexual reproduction
Body cells
Section 11-1Standards addressed: CA 3.b. Students know the genetic basis for Mendel’s laws of segregation and independent assortment. National 7 2.c. Students know an inherited trait can be determined by one or more genes. 7.2.d. Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining phenotype while the other is recessive. B1. 2.d. Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization).
Key Ideas: What is the principle of dominance?What happens during segregation?
INTRODUCTION TO GENETICS I. The work of Gregor Mendel
A. : the scientific study of heredity
B. Heredity: II. Gregor Mendel's Peas
A. In the 1800's, _____________________________ (an Austrian Monk) conducted the first scientific study of heredity using pea plants.
B. Pea plants contain both
male (pollen:sperm) and female (eggs) reproductive parts.
Genetics
Passing genes from generation to generation
Gregor Mendel
Flowering Plant Structures: Pea Plant
C. _______________ = Joining of male and female reproductive cellsFertilization
D. _________________= a pea plant whose pollen fertilizes the egg cells in the very same flower.
1. Mendel discovered that some plants ___________ for certain traits
2. Trait=
Example: seed color, plant height
3.True breeding (a.k.a. pure)=
Example: Short plants that self pollinate for
generations always produce offspring that were pure for shortness.
Self-pollination
“Bred True”
Specific Characteristics
Peas that are allowed to self-pollinate produce offspring identical to themselves
E. _______________= male sex cells from one flower pollinate a female sex cell on a different flower.
Cross-pollination
F. Mendel manually cross pollinated pea plants, removing the male parts to ensure no self-pollination would occur. Through a series of experiments, Mendel was able to make discoveries of basic principles of heredity.
1. principle of
2. principle of
3. principle of
Dominance
Independent Assortment
Segregation
A. Mendel studied __ different traits in pea plants each with 2 contrasting characters. (refer to page 264) B. Each trait Mendel studied was controlled by one gene. C. Different forms of a gene (trait) = Example: Gene for plant height has 2 alleles
Alleles
Dominant: T = tall Recessive: t = short
7
III. Experiments Mendel performed
Seed Shape
Flower Position
Seed CoatColor
Seed Color
Pod Color
Plant Height
PodShape
Round
Wrinkled
Round
Yellow
Green
Gray
White
Smooth
Constricted
Green
Yellow
Axial
Terminal
Tall
Short
Yellow Gray Smooth Green Axial Tall
Section 11-1
Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants
Go to Section:
Mendel’s Seven Crosses on Pea Plants
Parent Offspring
pure bred tall x pure bred tall TT X TT
All plants are
pure bred short x pure bred short tt X tt
All plants are
Pure bred tall x pure bred short X
All plants are
Mendel Experiment #1:
TALL
SHORT
TT tt TALL
· individual factors (now known as _________) · the factors
________________________________= some alleles are dominant (expressed trait;written as a capital letter; ex. T) some are recessive (hidden/masked trait; written as a lower case letter; ex. t) From these conclusions, Mendel wanted to continue his experiments to see what happened to the recessive trait
genes
did not blend
Principle of Dominance
Conclusion:
P Generation F1 Generation F2 Generation
Tall Short Tall TallTall Tall Tall Short
Section 11-1
Principles of Dominance
Go to Section:
P Generation F1 Generation F2 Generation
Tall Short Tall TallTall Tall Tall Short
Section 11-1
Principles of Dominance
Go to Section:
P Generation F1 Generation F2 Generation
Tall Short Tall TallTall Tall Tall Short
Section 11-1
Principles of Dominance
Go to Section:
3 tall : 1 short
Conclusion:· ___________________________: The reappearance of the recessive allele indicated that at some point the allele for shortness separated from the allele for tallness. Mendel suggested that the alleles separated during the formation of the sex cells (gametes)….During meiosis.
Principle of Segregation
A. Probability =
B. Probability=
Example #1: If you flip a coin, what is the probability of landing on heads? Probability= (side that has a head on it) ( opportunities on a coin; head or tails) Example #2: If you flip a coin 3 times what is the probability of landing on heads? Probability=
The likelihood that a particular event will occur
# of times a particular event occurs# of opportunities for the event to occur (# of trials)
122
½ x ½ x ½ = 1/8
IV. PROBABILITY AND PUNNETT SQUARES
A. Each flip is
B. The C. The principles of probability can be used to
independent of the next. Past outcomes do not affect future ones. Similar to alleles that segregate randomly, like a coin flip.
larger the number of trials the closer you get to the expected outcomes
predict the outcomes of genetic crosses.
IV. PUNNETT SQUARES Use of Punnett squares help determine the probable outcomes of genetic crosses.· New vocabulary to help with Punnett squares -Homozygous = -Heterozygous= -Genotype= -Phenotype= -Hybrids=
Having 2 identical alleles (TT, tt)Having 2 different alleles (Tt)
Genetic makeup of an organism (TT, tt, Tt)Physical appearance (tall or short)
The offspring resulting from a cross between parents of contrasting traits
· Example of a Punnett square: Parent (P) cross
homozygous tall( ) x homozygous short( )
Probability of producing homozygous tall offspring?
Probability of producing hybrid?
TT tt
0/4
4/4
F1
offspring
t t
Tt
T
T
TtTt
Tt
IV. PROBABILITY AND SEGREGATIONA. For fun, lets cross F1’s to see if Mendel’s assumptions
about segregation are correct:
Tt x Tt
If the alleles segregate during meiosis, then the probable outcomes will be:
TT= Tall=Tt= Short=tt= Ratio tall:short=
1/42/4
1/4
31
3:1
t
T
T t
TT Tt
Tt tt
Conclusion:
IV. PROBABILITY AND INDEPENDENT ASSORTMENT
A. Mendel wondered if one pair of alleles affected the segregation of another pair of alleles. B.The two factor cross: Mendel crossed RRYY x rryy (P)(aka:two trait cross)
All offspring are
Mendel was correct in his assumptions about Segregration
Do round seeds have to be yellow?
Hybrid (RrYy) (F1)
A. Then he crossed the hybrids (F1):
RrYy x RrYy· Punnett square formatting rules for 2 trait crosses 1. Determine the possible gametes produced by the parents. 2 methods: a. F- RrYy O- I- L-
irst twoutside two
nside twoast two
(RY)(Ry)(rY)(ry)
a. Use a punnett square. One trait on top and the other trait on the side.
Parent 1: RrYy Parent 2: RrYy
Possible gametes Possible gametes
RyRY
ryrY ryrY
RyRY
r
R
yY yY
R
r
2. Place one parent’s gametes at the top of a 16-Punnett square and the other parent’s gametes on the side of the 16-Punnett square.
RY
RY
Ry
Ry
rY
rY
ry
ry
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Section 11-3
Go to Section:
Probability: RY (round and yellow)= Ry (round and green =rY (wrinkled and yellow)= ry (wrinkled and green)= Phenotype Ratio= Conclusion=
9/163/16
3/161/16
9:3:3:1
Alleles for seed shape independently assort.
****This is true if the traits you are studying Just by chance all 7 of Mendel’s traits were on different chromosomes.
Genes for different traits can segregate independently during the formation of gametes
are located on different chromosomes
Independent assortment
1. The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring.2. In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.3. In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed.4. The alleles for different genes usually segregate independently of one another.
**Summary of Mendel’s Principles**
concluded that
which is called the
which is called the
GregorMendel
Law ofDominance
Law ofSegregation
Peaplants
“Factors”determine
traits
Some alleles are dominant,
and some alleles are recessive
Alleles are separated during gamete formation
experimented with
Summary of Gregor Mendel’s Work
Key idea: Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.
Ex. Four O’clock flowers (see next slide)
Beyond Dominant and Recessive Alleles
Incomplete Dominance in Four O’clock Flowers
Incomplete Dominance: One allele is _______________ dominant over another. Therefore the phenotype in the heterozygous is somewhere __________ the two homozygous phenotypes.
not completely
in between
Codominance: both alleles contribute _________ to the phenotype. Ex. Cholesterol
Mutliple Alleles: Genes that have _____________
alleles.This does not mean an individual can have more than two alleles, but that there are more than two alleles in the _______________ for a given trait.
Ex. Rabbit coat color, blood type
equally
more than two
population
BO
BB
Multiple Alleles and Codominance
3 Alleles: iA, iB, I
iA and iB are codominant
iA, iB both dominate over i
Blood Type/Phenotype
Polygenic Inheritance: The interaction of many genes controls one trait.
It is usually recognized in traits that show a ____________________ such as skin color, height, and body weight.
range of phenotypes
Applying Mendel’s Principles. Mendel’s principles do not apply only to plants. Thomas Hunt Morgan1. In the early ________, Morgan (a nobel prize winning geneticist) decided to look for a model organism to advance the study of genetics.2. He studied the _____________, Drosophila melanogaster.3. This specimen was a good choice because: _______ and can be kept in a small place produce ___________ of offspring has only _________ of chromosomes they can produce a new _______________ every 4 weeks
1900’s
fruit fly
tiny hundreds 4 pairs
generation
Genes alone ______________________ the characteristics of an organism. The interaction between genes and the ________________are necessary. Ex. Consider the height of a sunflower. Genes provide a plan for the development of a sunflower but the condition of the soil, climate, and water availability will also influence the height of the sunflower.
do not determine
environment
Genetics and the environment
11-5: Gene Linkage and Gene MapsStandards addressed: CA B1 3.b students know the genetic basis forMendel’s laws of segregation and independent assortment. *B1 3.d. Students know how to use data on frequency of recombination at meiosis to estimate genetic distances between loci and to interpret genetic maps of chromosomes. Key concept: What structures actually assort independently?
Actually ________________________ do assort independently just as Mendel had suggested but the _______ on the chromosomes can be ____________.
A. Linked genes1. Genes located on the _________ chromosome2. Inherited _____________3. Do not undergo ___________________; they don't follow Mendel's law (Just by chance all the traits Mendel studied were located on separate chromosomes...none were linked.)
the chromosomes
genes linked together
same
together independent assortment
B. Linkage group= all the genes on a _____________
* If there are ___ pairs of chromosomes then there are ____ linkage groups. Humans have ____ pairs of chromosomes therefore ____ linkage groups
chromosome
4 4 23
23
III. Crossing OverA. If two genes are found on the same chromosome, does it mean that they are linked forever? NO! Crossing over produces ___________________
B. Recombinants= individuals with _________________ of genes
recombinants.
new combinations
IV. Gene Mapping
A. Sturtevant stated that: crossing over occurs ________________ along the linkage groups. the _______________ the genes are from each other the ______________ they will cross over using the _______________________ (how often crossing over occurs), a gene _______ can be made for each chromosome
randomly
further more likely
frequency of recombination
map
B. Gene map= the __________________ on a chromosome Example: gene a and gene b cross over 20%
gene a and gene c cross over 5% gene b and gene c cross over 75%
chromosome:
positions of genes
C A B