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16-1 Genes and Variation
16-1 Genes and Variation
Photo credit: ©MURRAY, PATTI/Animals Animals Enterprises
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2. 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.
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3. 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.
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Gene Pool Practice
Take the next couple minutes to complete the Gene Pools worksheet.
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5. Variation and Gene Pools
In genetic terms, evolution is any change in the relative frequency of alleles in a population.
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6. Sources of Genetic Variation
The two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction.
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7. Sources of Genetic Variation
Mutations
A mutation is any change in a sequence of DNA.
Mutations do not always affect an organism’s phenotype.
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8. 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?
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9. Single-Gene and Polygenic Traits
The number of phenotypes produced for a given trait depends on how many genes control the trait.
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10. 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.
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11. 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?
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12. 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.
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13. Polygenic Traits Practice
Take the next couple minutes to complete the Polygenic Traits worksheet.
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16-1
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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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