1. Chapter 16

2.  16-1 Genes & Variation

3.  1. Genetic Variation is common

4.   Most organisms have many different alleles (forms of a gene) for one trait  Genetic variation seems invisible  There are small differences in biochemical process like cell respiration.

5.  2. Variation & Gene Pools

6.   Populations are used to study genetic variation  Gene Pool- A common group of genes shared by a population.  Ex: the gene pool of a population of maple trees in a park

7.   Relative Frequency- the number of times an allele occurs in a gene pool in comparison to the number of times the other alleles occur for the same gene.  Is expressed as a percentage  Relative frequency has nothing to do with the gene being dominant or recessive.  Ex: In a population of cats the relative frequency of the dominate allele (B) is 65% & the relative frequency of the recessive allele (b) is 35%

8.   Gene Pool for Fur Color in Mice

9.   Evolution is any change in the relative frequency of alleles in a population

10.  3. Sources of Genetic Variation

11.   There are two main sources of genetic variation:  Mutation  Gene Shuffling

12.   Mutations (a change in the sequence of DNA)  Can happen b/c of mistakes during DNA Replication  Exposure to radiation  Exposure to chemicals in the environment  Sometimes mutations affect the phenotype of an organism; sometimes they do not  Mutations can affect the “fitness” of an organism

13.   Gene Shuffling  Occurs during when gametes are made  Also occurs crossing over during meiosis  Is the result of most genetic variation

14.  4. Single-Gene & Polygenic Traits

15.   Depends on how many genes control the trait  Traits can be single-gene or polygenic  Single-gene trait- a trait that is controlled by one gene w/ two alleles  Ex: a widow’s peak in humans What Determines How Many Phenotypes A Population Has?

16.   In this example population having a widows peak is more common than not having a widows peak.

17.   Many traits are polygenic  Polygenic trait- a trait that controlled by two or more genes  b/c each gene of a polygenic trait has two or more alleles there are many different phenotypes that can result  Hair color in humans  Body height in humans  Body shape in humans  Skin color in humans

18.   Phenotypes of brown skin in humans  Variations of brown hair color in humans. What is your hair color?

19.   A bell shaped cure represents the distribution of polygenic traits in humans.  This is called “normal distribution”  Most people are in the middle  Very people are on either extreme very light brown or very dark brown. Very tall or very short