1. Evolution of populations
Chapter 17

2. Key concepts How is evolution defined in genetic terms?
What are the sources of genetic variation?
What determines the number of phenotypes for a given trait?

3. Genotype and Phenotype in Evolution
Particular combinations of alleles it carries
Aa, Bb
Phenotype:
Includes all physical, psychological, and behavioral characteristics of an organism
Eye color or height
Natural selection acts directly on PHENOTYPE, not genotype

4. Populations and Gene Pools
Evolution, in genetic terms, involves a change in the frequency of alleles in the population over time.
Population: a group of individuals of the same species that mate and produce offspring
Allele frequency: the number of times an allele occurs in a gene pool
Gene pool: consists of all the genes, including all the different alleles for each gene, that are present in a population

5. Sources of Genetic Variation
Mutation 1
Genetic recombination during sexual reproduction 2
Lateral gene transfer 3

6. mutation
Any change in the genetic material of a cell
Individual genes
larger pieces of chromosomes
Mutations that produce changes in phenotype may or may not affect fitness

7. Genetic Recombination in Sexual Reproduction
Inherit 23 chromosomes from mom, 23 from dad
8.4 million gene combinations
Crossing-over
Occurs during meiosis
Paired chromosomes swap lengths of DNA at random
This is why you don’t look like your siblings (unless you’re an identical twin)!
This is why individual members of a species differ from one another

8. lateral gene transfer
The passing of genes from one organism to another organism that is not its offspring
Example: bacteria swap genes on plasmids
Can occur between organisms of the same species or different species
Antibiotic resistance in bacteria

9. Single-Gene Traits
The number of phenotypes produced for a trait depends on how many genes control the trait
Single gene trait: a trait controlled by only one gene
Snail shells
Gene that controls banding has two alleles
Allele for a shell without banding is dominant

10. Polygenic Traits
polygenic trait: a trait controlled by two or more genes
each gene has two or more alleles
Human height:
Very short  very tall

11. Key concepts
How is evolution defined in genetic terms?
What are the sources of genetic variation?
What determines the number of phenotypes for a given trait?