Genetic Diagrams I - Eye
Color of Fruit Fly
A genetic diagram is an useful tool to help us predict the probability
of a characteristic of an organism. In the following example, the result of mating between a homozygous
white eye fruit fly and a homozygous red eye fruit fly are studied. It is known that the
allele for white eye is dominant over the allele for red eye.
Let W be the dominant allele for white eye.
Let w be the recessive allele for red eye.
Parent phenotype White eyed Red eyed
Parent genotype WW X ww
Gametes W w
Possible offspring genotype Ww
Offspring phenotype White eyed
the two fruit flies are homozygous, their homologous chromosomes has the same
alleles. When the homologous chromosomes separate during meiosis, the
white eyed fruit fly produces gametes containing alleles W and W,
while the red eyed fruit fly produces w and w gametes only. When
the two gametes, (one from mother and one from father), fuse during
fertilisation, only one type of cell results. The daughter cell contains
the allele Ww, and is heterozygous. But W is dominant over
w, therefore all the offspring must be white eyed.
and Maternal Chromosomes