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Sex-linked Genetic traits

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Predict the parental genotypes for individuals expressing the dominant or the recessive trait. What sex generally expresses the recessive trait? Why?

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Sex-linked traits are those carried on either the X or Y chromosome. Because females have two X chromosomes and males have XY the frequency of the trait is different from autosomal traits and is influenced by the sex of the organism.

For example, let's say a trait is dominant (A) and X-linked (this means that an individual only needs to inherit one copy of the dominant allele to express the trait).
XAXa x XaY
Xa XAXa XaXa
Y XAY ...

Solution Summary

Detailed explanation of how to predict if a trait is dominant, recessive, and/or sex-linked. Web references provided.

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Genetic crosses with sex linked traits are examined.

In J.R.R Tolkien's The Lord of the Rings, the Black Riders of Mordor ride steeds with eyes of fire. As a geneticist, you are very interested in the inheritance of the fire-red eye colour. A discovery is made that the eyes contains two types of pigments, brown and red, that are usually bound to core granules in the eye. In wild-type steeds, precursors are converted by these granules to the above pigments, but in steeds homozygous for the recessive X-linked gene w (white eye), the granules remain unconverted and a white eye results. The metabolic pathways for the synthesis of the two pigments are shown in the attached file. Each step of the pathway is controlled by a gene: mutation v results in vermillion eyes; cn results in cinnabar eyes; st results in scarlet eyes; bw results in brown eyes; and se results in black eyes. All these mutations are recessive to their wild-type alleles, and all are unlinked. For the following genotypes, show the proportions of steed eye phenotypes that would be obtained in the F1 of the given matings.

This case is answered.

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