Genetics and Evolution

Mary Susan Mardon

Nucleotides

• Building blocks of DNA and RNA.• Each nucleotide contains:

• phosphate group.• deoxyribose (DNA), ribose (RNA)

• nitrogen base.

* adenine * cytosine * thymine * guanine RNA only---Uracil

The Discovery of DNA’s Structure

• Rosalind Franklin and Maurice Wilkins at King’s College in England used x-ray diffraction to study the physical structure of DNA.

• James Watson and Francis Crick worked at Cambridge University in London, England created a structural model of DNA.

The Structure of DNA

• Deoxyribonucleic acid (DNA) is located in the nucleus.

• Double helix.• Each side of the helix is composed of a long

strand of nucleotides.• DNA has four nitrogen bases--adenine,

thymine, guanine and cytosine.

DNA Function

• Provides genetic information in the form of a genetic code.

• DNA splits in half• Codon is transcribed to mRNA• tRNA picks the message up and transfers to

the ribosome where the message is translated into amino acids

• Proteins are then formed

RNA Function

• The function of RNA is protein synthesis.• Three basic steps to protein synthesis:

1. DNA segment must be copied in the nucleus.2. The code must be carried from the nucleus into the

cytoplasm and to a ribosome.3. The protein is assembled from the code and

released from the ribosome.

• Single stranded• Ribose• Adenine bonds

with Uracil • Cytosine bonds

with guanine• Three types of

RNA:1. Transfer2. Messenger3. Ribosome

Events of the Cell Cycle

• Interphase is composed of G1 phase-----Cell growth, synthesize new proteins, organellesS phase-----Chromosomes replicated, DNA synthesizedG2 phase-----production of molecules and organelles, shortest of the 3 phases

Mitosis

• Nuclear division.• Cell division results in two daughter cells. (2n)

Meiosis

A process called reduction division in which the number of chromosomes in a human reproductive cell is reduced to 23 chromosomes. These cells are haploid (n).

Genetics and Probability

• Gregor Mendel• Trait• Hybrid or Heterozygous—Hh• Purebred or Homozygous—HH, hh• Allele: variation of a gene• Dominant Trait—HH, Hh• Recessive Trait– hh• Gamete: Sex cells• Genotype: genes represented by letters (HH, Hh, hh)

Genetics and Probability continued

• Phenotype: traits or characteristics you can see.

• Punnett Square: A tool to calculate genetic probability.

• Cross-pollinate: two different parents.• Self-pollinate: one parent.• True breeders: can self-pollinate to produce

identical offspring.

Genetics and Probability continued

• Principle of Segregation: The paired alleles separate so that each egg or sperm carries one form of the allele.

• Principle of Independent Assortment: states that genes for different traits can segregate independently during the formation of gametes.

• Principle of Dominance: states that some forms of a gene or trait are dominant over other traits, which are called recessive (hides or masks)

Genetics and Probability continued

• Incomplete Dominance: one allele is not completely dominant over the other (RR, WW)

• Co-dominance: Both alleles contribute to the phenotype (BW)

• Polygenic Traits: more than one gene controls the trait (skin color)

• Evolution: Change over time

• Theory of Natural Selection: Organisms adapted to their environment survive and reproduce

Directional Stabilizing Disruptive

GENERATIONS

GENETIC VARIATIONS

Eliminated

Mean

EliminatedEliminated

Mean

Eliminated

Mean

Types of Natural Selection

• Stabilizing Selection: environmental change acts to eliminate extremes in a population

• Directional Selection: occurs in either direction shifting the population towards a new norm.

• Disruptive Selection: environmental change acts on the most common variety.

Requirements of a Species

• Species: group of similar organisms that can breed and produce fertile offspring.

• Genetic mutations (random changes in the DNA)• Genetic drift (change in frequency of alleles in a

population)• Hybridization• Gene Flow: exchange of genes between two

populations, development of geographic isolation, ex. Darwin’s finches

Animal Adaptation

• Behavioral adaption for survival and reproduction

• Territoriality is a behavioral adaption that ensures adequate space and resources for reproduction.

• Courting behavior is a behavioral adaption that helps to ensure beneficial genes are passed along to offspring.

Patterns of Evolution

• Gradualism: species change slowly over many generations; ex. body size of the water buffalo

• Punctuated Equilibrium: sudden changes in a species; ex. light and dark peppered moth

• Convergent Evolution: unrelated species develop similar characteristics; ex. porpoise and shark—streamlined bodies and fins

• Divergent Evolution: many species develop from a common ancestor; ex. homologous structures (beaks) in Darwin’s finches

Patterns of Evolution, continued

• Coevolution: two or more organisms in an ecosystem evolve in response to each other; ex. Orchid’s long tube and Hawk moth’s proboscis

Evidence of Evolution

• Anatomical Similarities• Homologous structures; ex. human arm, wing

of a bird, flipper of a whale• Vestigial organs; whales and some snakes have

a pelvis and femurs• Molecular Similarities: overlap of DNA; ex.

DNA of a Horseshoe crab is more closely related to a spider than a crab

Continued…

• Embryonic Developmental Similarities:

Continued…

• Fossil Record:

Continued…

• Extinction1. Ecological extinction: species does not have a

large enough population to sustain genetic diversity; ex. Florida panther, mountain lion

2. Mass extinction: large population becomes extinct in a short period of time