Lesson Overview17.1 Genes and Variation

Lesson Overview Genes and Variation

THINK ABOUT IT

Darwin developed his theory of evolution without knowing how heritable traits passed from one generation to the next or where heritable variation came from.

What would happen when genetics answered questions about how heredity works?

Lesson Overview Genes and Variation

Genetics Joins Evolutionary Theory

How is evolution defined in genetic terms?

Lesson Overview Genes and Variation

Genetics Joins Evolutionary Theory

How is evolution defined in genetic terms?

In genetic terms, evolution is any change in the relative frequency of alleles in the gene pool of a population over time.

Lesson Overview Genes and Variation

Genetics Joins Evolutionary Theory

Researchers discovered that heritable traits are controlled by genes.

Changes in genes and chromosomes generate variation.

For example, all of these children received their genes from the same parents, but they all look different.

Lesson Overview Genes and Variation

Genotype and Phenotype in Evolution

Natural selection acts directly on phenotype, not genotype.

Some individuals have phenotypes that are better suited to their environment than others. These individuals produce more offspring and pass on more copies of their genes to the next generation.

Lesson Overview Genes and Variation

Populations and Gene Pools

A population is a group of individuals of the same species that mate and produce offspring.

A gene pool consists of all the genes, including all the different alleles for each gene that are present in a population.

Lesson Overview Genes and Variation

Populations and Gene Pools

Researchers study gene pools by examining the relative frequency of an allele. The relative frequency of an allele is the number of times a particular allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur.

Lesson Overview Genes and Variation

For example, this diagram shows the gene pool for fur color in a population of mice.

Lesson Overview Genes and Variation

Populations and Gene Pools

Evolution is any change in the relative frequency of alleles in the gene pool of a population over time.

Natural selection operates on individuals, but resulting changes in allele frequencies show up in populations. Populations, rather than individuals, evolve.

Lesson Overview Genes and Variation

Mutations

Mutations that produce changes in phenotype may or may not affect fitness. Some mutations may be lethal or may lower fitness; others may be beneficial.

Mutations matter in evolution only if they can be passed from generation to generation. The mutation must occur in the germ line cells that produce either eggs or sperm.

Lesson Overview Genes and Variation

Genetic Recombination in Sexual Reproduction

Mutations that produce changes in phenotype may or may not affect fitness. Some mutations may be lethal or may lower fitness; others may be beneficial.

Mutations matter in evolution only if they can be passed from generation to generation. The mutation must occur in the germ line cells that produce either eggs or sperm.