1. 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?

2. 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

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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
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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
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6. 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.
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7. 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.
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A. gene pool- all genes (& alleles) in a population.
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9. 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

10. 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. 
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11. Variation and Gene Pools
Evolution is any change in the relative frequency of alleles in a population.
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12. 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.
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13. 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.
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14. 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
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15. Crossing-Over

16. What are 2 main sources of genetic variation?
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17. 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.

18. 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.
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19. Single-Gene and Polygenic Trait
B. Polygenic traits- controlled by 2 or more genes.
-Many phenotypes
-Height in humans
-Bell shaped curve
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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.
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16-1
Most inheritable differences are a result of
gene shuffling.
frequency of alleles.
mutations.
DNA replication.
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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.
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16-1
A widow's peak in humans is an example of a(an)
invariable trait.
single-gene trait.
polygenic trait.
mutation.
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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.
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