Flashcards Ch 14 Notes Part III - Inheritance Patterns

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_____________ is a type of inheritance where one allele is not completely dominant over the other.

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Incomplete dominance

The result is a heterozygote with an intermediate phenotype.

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Example of incomplete dominance in 4 o’clock flowers.

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RR = red flowers, WW = white flowers, RW = pink flowers.

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Example of incomplete dominance in Andalusian chickens.

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BB (black feathers) x WW (white feathers) = BW "blue" feathers in offspring.

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Polygenic Inheritance

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A mode of inheritance where the additive effect of two or more genes determines a single phenotypic character.

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Examples of Polygenic Traits

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- Human height (many genes) - Human hair color (at least 2 gene pairs) - Human eye color (2 main gene pairs) - Human skin color (many) - Beak depth

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polygenic beak depth variation

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Diagram showing polygenic beak depth variation

Illustrates the variation in beak depth as a polygenic trait, showing frequency distribution.

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Eye color as an example of a polygenic trait

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Eye color is influenced by two main genes, but at least 14 other genes also contribute to the final eye color.

The pigment melanin helps color the iris, and small color differences arise from different combinations of alleles.

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Genetic combinations of wheat kernel pigment with different genotypes and their corresponding color intensities.

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The diagram illustrates the combinations of alleles (A, B, C) and their effects on pigment intensity in wheat kernels, showing a range of colors from dark red to white.

Three genes that make reddish pigment in wheat kernels are called A, B, and C. Each gene comes in two alleles: one capital-letter allele that makes pigment and one lowercase allele that does not.

The alleles have additive effects: - The aa genotype contributes no pigment. - The Aa genotype contributes some pigment. - The AA genotype contributes more pigment (twice as much as Aa). The same applies to the B and C genes.

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Epistasis

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Interaction between the alleles of two different genes in which one modifies the phenotypic expression of the other. (One gene is in charge of gene expression of a 2nd gene)

In this example, the mice must have at least one dominant C allele to show any color. If they are cc, the are albino. Gene C controls expression of gene A.

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Epistasis in mice

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Gene for pigment deposition is epistatic to the gene for melanin production in mice.

The albino mouse can make melanin, but the allele for depositing the color into the hair shaft controls whether you see that produced melanin.