Genes and VariationGenes and Variation

16-1 This section describes the 16-1 This section describes the main sources of heritable main sources of heritable variation in a population. It variation in a population. It also explains how phenotypes also explains how phenotypes are expressed. are expressed.

Introduction Introduction Is the following sentence true or false? Is the following sentence true or false?

Mendel’s work on inheritance was Mendel’s work on inheritance was published after Darwin’s lifetime. published after Darwin’s lifetime.

FALSEFALSE

DARWIN’s ORIGIN of SPECIESDARWIN’s ORIGIN of SPECIES

Which two important factors was Which two important factors was Darwin unable to explain without an Darwin unable to explain without an understanding of heredity?understanding of heredity?

He was unable to explain the source He was unable to explain the source of variation and how heritable traits of variation and how heritable traits were passed from one generation to were passed from one generation to the next. the next.

How Common Is Genetic How Common Is Genetic Variation Variation

All organisms have All organisms have additional __________that additional __________that is “invisible” because it is “invisible” because it involves small differences involves small differences in biochemical processesin biochemical processes. .

genetic variationgenetic variation

Variation and Gene Pools Variation and Gene Pools

A group of individuals of the same A group of individuals of the same species that interbreed is a(an) ____. species that interbreed is a(an) ____.

populationpopulation

GENE VARIATIONGENE VARIATION

All of the genes in a population are All of the genes in a population are called a(an)____.called a(an)____.

gene poolgene pool

GENE VARIATIONGENE VARIATION Is the following sentence true or Is the following sentence true or

false?false?

A gene pool typically contains just A gene pool typically contains just one allele for each inheritable trait. one allele for each inheritable trait.

false false

GENE VARIATIONGENE VARIATION

The number of times that an allele The number of times that an allele occurs in a gene pool compared with occurs in a gene pool compared with the number of times other alleles for the number of times other alleles for the same gene occur is called the the same gene occur is called the ______________ of the allele.of the allele.

relative frequencyrelative frequency

GENE VARIATIONGENE VARIATION

Evolution of Populations Evolution of Populations Sources of Genetic Variation Sources of Genetic Variation

What is a mutation?What is a mutation?

It is any change in a sequence of It is any change in a sequence of DNA. DNA.

GENE VARIATIONGENE VARIATION

Why do mutations occur? Why do mutations occur?

They occur because of mistakes in They occur because of mistakes in the replication of DNA or as a result the replication of DNA or as a result of radiation or chemicals in the of radiation or chemicals in the environment. environment.

GENE VARIATIONGENE VARIATION

Circle the letter of each choice that is true Circle the letter of each choice that is true about mutations.about mutations. They do not always change an amino acidThey do not always change an amino acid

GENE VARIATIONGENE VARIATION

Is the following sentence true or false?Is the following sentence true or false?

Most heritable differences are due to Most heritable differences are due to gene shuffling that occurs during the gene shuffling that occurs during the production of gametes.production of gametes.

TRUETRUE

GENE VARIATIONGENE VARIATION Circle the letter of each choice that is true about Circle the letter of each choice that is true about

sexual reproduction.sexual reproduction. It is a major source of variation in many It is a major source of variation in many

populations. populations.

It can produce many different phenotypes.It can produce many different phenotypes.

It can produce many different genetic combinations.It can produce many different genetic combinations.

GENE VARIATIONGENE VARIATION Single-Gene and Polygenic Traits Single-Gene and Polygenic Traits

Is the following sentence true or false? Is the following sentence true or false?

The number of phenotypes produced for a given The number of phenotypes produced for a given trait depends on how many genes control the trait depends on how many genes control the trait. trait.

TRUETRUE

GENE VARIATIONGENE VARIATION

Is the following sentence true or false?Is the following sentence true or false?

Most traits are controlled by a single gene. Most traits are controlled by a single gene.

false false

GENETIC VARIATIONGENETIC VARIATION

Polygenic Trait Single-Gene Trait

Label the two graphs to show which one represents a single-gene trait and which one represents a polygenic trait.