Skip navigation. That year, Morgan was breeding Drosophilaor fruit flies. After observing thousands of fruit fly offspring with red eyes, he obtained one that had white eyes.
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.
We take it for granted today that DNA is the genetic material, and therefore our genes must be located on chromosomes. But like all facts in science, this idea had to be repeatedly tested and found to be true before it could be accepted as fact. The chromosome theory of inheritanceor the idea that genes are located on chromosomes, was proposed based on experiments by Thomas Hunt Morgan using Drosophila melanogasteror fruit flies.
This page has been archived and is no longer updated.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.
Sex linkage is the patterns of inheritance and presentation when a gene mutation allele is present on a sex chromosome allosome rather than a non-sex chromosome autosome. They are characteristically different from the autosomal forms of dominance and recessiveness as they are different depending on the sex of the individual. Since humans have several times as many genes on the female X chromosome than on the male Y chromosomeX-linked traits are much more common than Y-linked traits.
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. The tan-bodied, white-eyed male is hemizygous for both the recessive white-eye color and the dominant tan-body color.
The chromosomes present in the diploid cells of the majority of the sexually reproducing animals are of two types: autosomes bearing genes for somatic characters and sex chromosomes bearing genes for sex. Sex chromosomes also carry some genes for non-sexual characters such as colour blindness and haemophilia. Such genes which are always associated with sex chromosomes are called sex-linked genes.