An inheritance pattern in which the heterozygote has an intermediate phenotype because neither allele completely masks the other.

An inheritance pattern in which both alleles are distinctly expressed in the heterozygote.

More than two forms of a gene exist in a population, although each diploid individual carries only two.

Having only one allele for a gene, as an XY individual often does for an X-linked gene absent from the Y chromosome.

An interaction in which one gene masks or interferes with the expression of another gene.

GeneticsLesson 2 of 2 in the course Patterns of Inheritance

Inheritance Beyond Simple Dominance: Sex Linkage, Linkage, and Gene Interactions

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Mendel’s pea-plant traits followed a relatively simple pattern: one allele was dominant and the other recessive. Other inheritance patterns show that alleles can interact in different ways while the basic principles of inheritance still apply.

In incomplete dominance, neither allele completely masks the other. A heterozygote has a phenotype intermediate between the phenotypes of the two homozygotes. In snapdragons, crossing a red-flowered plant ( $C^R C^R$ ) with a white-flowered plant ( $C^W C^W$ ) produces pink heterozygotes ( $C^R C^W$ ). The red allele’s pigment is diluted in the heterozygote, producing pink petals.

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Incomplete dominance: An inheritance pattern in which the heterozygote has an intermediate phenotype because neither allele completely masks the other.
Codominance: An inheritance pattern in which both alleles are distinctly expressed in the heterozygote.
Multiple alleles: More than two forms of a gene exist in a population, although each diploid individual carries only two.
Hemizygous: Having only one allele for a gene, as an XY individual often does for an X-linked gene absent from the Y chromosome.
Epistasis: An interaction in which one gene masks or interferes with the expression of another gene.

Quiz questions

An XY individual has one allele for an X-linked gene that is absent from the Y chromosome. What is this allele state called?Answer: Hemizygous
For two linked genes, what generally happens to recombination frequency as the genes are farther apart on a chromosome?Answer: It generally increases.
In fruit flies, red eyes are associated with dominant $X^W$ . A heterozygous red-eyed female ( $X^W X^w$ ) is crossed with a red-eyed male ( $X^W Y$ ). What eye-color phenotype do all daughters have?Answer: Red eyes, because each daughter inherits $X^W$ from her father.
In mice, $cc$ prevents pigment, while $A\_$ produces agouti and $aa$ produces solid-colored fur when pigment is present. Why does $cc$ mask the effect of the A gene?Answer: The C gene is epistatic because $cc$ prevents pigment expression.
Which pattern is characteristic of a polygenic trait?Answer: Several genes contribute, often producing a range of phenotypes.

Based on Concepts of Biology by Samantha Fowler, Rebecca Roush, James Wise (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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