1. The Variability of Natural Populations

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Description and Tags

Evo. Pop. Gen.

17 Terms

1
Classical Hypothesis - Fisher and Muller
  • Worked with single gene traits in natural populations

  • Low population variability, low heterozygote frequency

  • Alternative alleles are harmful

  • Main evolutionary force- directional selection

  • Species variability given mainly by between-population variation

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2
Balance hypothesis - Dobzhansky and Wright
  • Examined the chromosomal polymorphisms in Drosophila populations

  • Natural populations are generally variable w/ high heterozygosity

  • Dominating force: Overdominant selection

  • Species variability given within-population variation

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3
Phenotypic variation
Variability in phenotypes that exists in a population. (Ex: height, weight, and body shape, hair, eye color, and the ability to roll your tongue)
Variability in phenotypes that exists in a population. (Ex: height, weight, and body shape, hair, eye color, and the ability to roll your tongue)
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4
Qualitative Traits

A trait that can be described as a category (Ex: black or red coat color, horned or polled, coat color dilution)

Example: Stem color of tobacco

  • Have 1 or 2 genes

  • Have few genotypes

  • Phenotypic categories

<p>A trait that can be described as a category (Ex: black or red coat color, horned or polled, coat color dilution)</p><p>Example: Stem color of tobacco</p><ul><li><p>Have 1 or 2 genes</p></li><li><p>Have few genotypes</p></li><li><p>Phenotypic categories</p></li></ul>
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5
Quantitative traits

A characteristic controlled by multiple genes as well as the environment (Ex: IQ, blood pressure, height, and weight)

Example: Number of grains of wheat

  • Have many genes

  • Many genotypes

  • Continuous distribution of the phenotypes

<p>A characteristic controlled by multiple genes as well as the environment (Ex: IQ, blood pressure, height, and weight)</p><p>Example: Number of grains of wheat</p><ul><li><p>Have many genes</p></li><li><p>Many genotypes</p></li><li><p>Continuous distribution of the phenotypes</p></li></ul>
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6
Peppered moth (biston betalaria)
  • Example of a qualitative trait

  • Involves two phenotypes: peppered (recessive), and carbonara (dominant)

<ul><li><p>Example of a qualitative trait</p></li><li><p>Involves two phenotypes: peppered (recessive), and carbonara (dominant)</p></li></ul>
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7
Wing traits of brown argus (Tricia artierxes issuekutzi)
  • Example of a quantitative trait

  • In small populations, evolutionary forces (ex: environmental changes) have a bigger effect, causing more drift and variation

<ul><li><p>Example of a quantitative trait</p></li><li><p>In small populations, evolutionary forces (ex: environmental changes) have a bigger effect, causing more drift and variation</p></li></ul>
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8
Birth mass of mice
  • Example of a quantitative trait

  • Each population was found to have its own phenotypic average, and its own variance (differences)

<ul><li><p>Example of a quantitative trait</p></li><li><p>Each population was found to have its own phenotypic average, and its own variance (differences)</p></li></ul>
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9
What makes up phenotypic variation?
Genotypic variation and Environmental variation
Genotypic variation and Environmental variation
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10
Genotypic variance
Genotypic variance
The final phenotypes of heterozygous offspring (Example: AA, Aa, aa)
The final phenotypes of heterozygous offspring (Example: AA, Aa, aa)
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11
Environmental variance
Environmental variance
Causes continuous distribution in final phenotypes of heterozygous offspring (Example: all the different varieties of Aa)
Causes continuous distribution in final phenotypes of heterozygous offspring (Example: all the different varieties of Aa)
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12
Phenotypic Variance equation: 
Vp = Vg + Ve + Vge

Phenotypic variance= genotypic+ environmental+interaction
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13
If Vge = 0
Genes and the environment do not interact
Genes and the environment do not interact
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14
If Vge > 0
There is interaction between genes and the environment
There is interaction between genes and the environment
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15
Genetic variance equation
Vg = Va + Vd + Vi

* Interactions between genes
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16
Additive model
Deviation from the avg. phenotype due to inheriting a particular allele

* Additive interaction between alleles: heterozygous individuals are a mid-point between the alleles
Deviation from the avg. phenotype due to inheriting a particular allele

* Additive interaction between alleles: heterozygous individuals are a mid-point between the alleles
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17
Dominance model
Deviation due to the interactions between alternative alleles at a specific locus (location on a chromosome)

* Heterozygous individuals resemble each other more
Deviation due to the interactions between alternative alleles at a specific locus (location on a chromosome)

* Heterozygous individuals resemble each other more
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