Warm Up 6 3/4 Phenotype allele Gene genotype Chemical factors that determine traits Different forms of a trait Visible trait Genetic makeup What did Mendel discover? What did Darwin discover?

Darwin was at a disadvantage when developing the theory of evolution due to his lack of understanding of how genes worked. He could not explain The source of variation How inheritable traits were passed from one generation to the next Ch. 16 Evolution of Populations

Copyright Pearson Prentice Hall 16-1 Genes and Variation 16-1 Genes and Variation Gene combinations & variations in traits can lead to evolution of species. Photo credit: ©MURRAY, PATTI/Animals Animals Enterprises Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall I. Variation and Gene Pools a. gene pool b. relative frequency II. Sources of Genetic Variation a. mutations b. gene shuffling III. Single-Gene and Polygenic Traits Copyright Pearson Prentice Hall

How Common Is Genetic Variation? Many genes have at least two forms, or alleles. All organisms have genetic variation that is “invisible” because it involves small differences in biochemical processes. An individual organism is heterozygous for many genes. Copyright Pearson Prentice Hall

Variation and Gene Pools I. Variation and Gene Pools Studied by populations. A population is a group of individuals of the same species that interbreed. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall A. gene pool- all genes (& alleles) in a population. Copyright Pearson Prentice Hall

Variation and Gene Pools B. Relative frequency- how often alleles shows up in gene pool % Not related to whether an allele is dominant or recessive

Variation and Gene Pools Gene Pool for Fur Color in Mice Sample Population Frequency of Alleles allele for brown fur allele for black fur When scientists determine whether a population is evolving, they may look at the sum of the population’s alleles, or its gene pool. This diagram shows the gene pool for fur color in a population of mice.  Copyright Pearson Prentice Hall

Variation and Gene Pools Evolution is any change in the relative frequency of alleles in a population. Copyright Pearson Prentice Hall

Sources of Genetic Variation II. Sources of Genetic Variation The two main sources of genetic variation are Mutations genetic shuffling that results from sexual reproduction. Copyright Pearson Prentice Hall

Sources of Genetic Variation A. Mutations A mutation is any change in a sequence of DNA. Mutations occur because of mistakes in DNA replication or as a result of radiation or chemicals in the environment. Mutations do not always affect an organism’s phenotype. Copyright Pearson Prentice Hall

Sources of Genetic Variation B. Gene Shuffling- occurs during gamete formation Most heritable differences are due to gene shuffling. Crossing-over exchange of genetic material 23 chromosomes produce 8.4 million different combinations Copyright Pearson Prentice Hall

Crossing-Over

What are 2 main sources of genetic variation? Copyright Pearson Prentice Hall

Single-Gene and Polygenic Traits III. Single-Gene and Polygenic Traits The number of phenotypes produced for a given trait depends on how many genes control the trait.

Single-Gene and Polygenic Traits A. Single-gene trait-controlled by one gene -2 phenotypes In humans, a single gene with two alleles controls whether a person has a widow’s peak (left) or does not have a widow’s peak (right). As a result, only two phenotypes are possible. The number of phenotypes a given trait has is determined by how many genes control the trait. Copyright Pearson Prentice Hall

Single-Gene and Polygenic Trait B. Polygenic traits- controlled by 2 or more genes. -Many phenotypes -Height in humans -Bell shaped curve Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 16-1 Which of the following statements is TRUE? The relative frequency of an allele is not related to whether the allele is dominant or recessive. Mutations always affect an organism's phenotype. Crossing over decreases the number of different genotypes that appear in an offspring. Evolution does not affect the frequency of genes in a gene pool. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 16-1 Most inheritable differences are a result of gene shuffling. frequency of alleles. mutations. DNA replication. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 16-1 The main sources of inherited variation are gene shuffling and mutations. gene pools and frequencies. single-gene and polygenic traits. genotypes and phenotypes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 16-1 A widow's peak in humans is an example of a(an) invariable trait. single-gene trait. polygenic trait. mutation. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 16-1 A graph of the length of the little finger on the left hand versus the number of people having fingers of a particular length is a bell-shaped curve. This indicates that finger length is a single-gene trait. polygenic trait. randomly inherited trait. strongly selected trait. Copyright Pearson Prentice Hall