1. Lesson Overview
17.1 Genes and Variation

2. 17.1 Genes and Variation
In terms of genetics, evolution is a change in the frequency of alleles in a population over time.

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

4. 3. Allele frequency is the number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene.

5. Sample Population
48% heterozygous black
36% homozygous brown
16% homozygous black
Frequency of Alleles
allele for brown fur
allele for black fur

6. 4. Three sources of genetic variation are mutation, genetic recombination during sexual reproduction, and lateral gene transfer.
5. A mutation is any change in the genetic material of a cell.

7. 6. Genetic recombination- the new combinations of genes produced by crossing over and independent assortment.
A)Independent assortment -occurs during sexual reproduction- remember that each chromosome in a pair moves independently of each other during meiosis
B)Crossing over - occurs during meiosis when homologous pairs of chromosomes are side by side; another way genes are recombined; leads to a number of new genotypes

8. 7. Lateral gene transfer - passing of genes from one organism to another organism that is not its offspring
8. The number of phenotypes produced for a trait depends on how many genes control the trait.

9. 9. single-gene trait—a trait controlled by only one gene ; results in fewer phenotypes

10. 10. polygenic traits - traits controlled by two or more genes