Evolution of populations Chapter 17
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?
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
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
Sources of Genetic Variation Mutation 1 Genetic recombination during sexual reproduction 2 Lateral gene transfer 3
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
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
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
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
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
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?