Sex-Linked Inheritance: Drosophila
Legend:
Drosophila are used to illustrate how alleles on sex chromosomes are inherited
in predictable patterns.
In sex-linked inheritance, alleles on sex
chromosomes are inherited in predictable patterns.
For example, in Drosophila the locus for eye color is located on the
X chromosome.
The allele for red eye color, which is normal in wild flies, is dominant
to the mutant allele for white eyes.
As females have two chromosomes X (with a locus for eye color), they
might be homozygous or heterozygous for either allele.
Males, who carry only one X chromosome, are always hemizygous. They
carry only the one X chromosome inherited from their mother, and it determines
their eye color.
In the left hand example, homozygous red eyed females (RR) mate
with hemizygous white eyed males (w-). In the offspring, all the
daughters are red eyed heterozygotes (Rw) and all sons are red eyed
hemizygotes (R-).
In the right hand, homozygous white eyed females (ww) mate with hemizygous
red eyed males (R-).
In the offspring, all the daughters are red eyed heterozygotes (Rw)
and all sons are white eyed hemizygotes (w-).
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