NCBI Bookshelf. An Introduction to Genetic Analysis. New York: W.
This page has been archived and is no longer updated. One day inAmerican geneticist Thomas Hunt Morgan peered through a hand lens at a male fruit fly, and he noticed it didn't look right. Instead of having the normally brilliant red eyes of wild-type Drosophila melanogasterthis fly had white eyes.
Males have one X and one Y-chromosome while females have two X-chromosomes. Due to the differences between the X and Y-chromosomes, the number and type of genes inherited by an individual depends on its sex. The genes present on the X and Y-chromosomes are called sex-linked genes.
What offspring would you expect from a cross between the female Drosophila described in problem 1 red eyes and a yellow body, homozygous recessive for the yellow body color allele and homozygous dominant for the eye color allele and the male described in problem 2 hemizygous for both the recessive white eye color allele and dominant tan body color allele? A reminder that the alleles for eye color and for body color are on the X chromosome of Drosophila, but not on the Y. Genotypes and phenotypes of parents The yellow-bodied, red-eyed female is homozygous for the dominant red-eye color and for the recessive yellow-body color.
A gene present on one of the sex chromosomes X or Y in mammals is a sex-linked trait because its expression depends on the sex of the individual. In humans, as well as in many other animals and some plants, the sex of the individual is determined by sex chromosomes. However, there are other sex determination systems in nature.
Averaged face of blue-eyed male subjects left. Averaged face of brown-eyed male subjects right. Czech population.
The color of the iris ranges on a continuum from very light blue to dark brown. Brown is the most frequent eye color worldwide. Lighter eye colors, such as blue and green, are found almost exclusively among people of European ancestry.
In humans, as well as in many other animals and some plants, the sex of the individual is determined by sex chromosomes—one pair of non-homologous chromosomes. Until now, we have only considered inheritance patterns among non-sex chromosomes, or autosomes. In addition to 22 homologous pairs of autosomes, human females have a homologous pair of X chromosomes, whereas human males have an XY chromosome pair.
In humans, as well as in many other animals and some plants, the sex of the individual is determined by sex chromosomes. The sex chromosomes are one pair of non-homologous chromosomes. In addition to 22 homologous pairs of autosomes, human females have a homologous pair of X chromosomes, whereas human males have an XY chromosome pair. Although the Y chromosome contains a small region of similarity to the X chromosome so that they can pair during meiosis, the Y chromosome is much shorter and contains many fewer genes.