Copyright Pearson Prentice Hall 16-1 Genes and Variation 16-1 Genes and Variation Photo credit: ©MURRAY, PATTI/Animals Animals Enterprises Copyright Pearson Prentice Hall

How Common Is Genetic Variation? Many genes have at least two forms. What is the vocab term for those forms? Alleles All organisms have genetic variation that is “invisible” because it involves small differences in biochemical processes. Copyright Pearson Prentice Hall

Variation and Gene Pools Genetic variation is studied in populations. A gene pool consists of all genes, including all the different alleles, that are present in a population. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Gene Pool Practice Take the next couple minutes to complete the Gene Pools worksheet. Copyright Pearson Prentice Hall

Variation and Gene Pools In genetic terms, evolution is any change in the relative frequency of alleles in a population. Copyright Pearson Prentice Hall

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

Sources of Genetic Variation Mutations A mutation is any change in a sequence of DNA. Mutations do not always affect an organism’s phenotype. Copyright Pearson Prentice Hall

Sources of Genetic Variation Gene Shuffling Most heritable differences are due to gene shuffling. Causes: Crossing-over (meiosis). Sexual reproduction. Does sexual reproduction alter the relative frequency of alleles in a population? Copyright Pearson Prentice Hall

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

Single-Gene and Polygenic Traits A single-gene trait is controlled by one gene that has two alleles. Variation in this gene leads to only two possible 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 Many traits are controlled by two or more genes and are called polygenic traits. One polygenic trait can have many possible genotypes and phenotypes. What is a polygenic trait we have already evaluated? Copyright Pearson Prentice Hall

Single-Gene and Polygenic Trait A bell-shaped curve is typical of polygenic traits. A bell-shaped curve is also called normal distribution. The graph below shows the distribution of phenotypes that would be expected for a trait if many genes contributed to the trait. Copyright Pearson Prentice Hall

Polygenic Traits Practice Take the next couple minutes to complete the Polygenic Traits worksheet. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 16-1 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