Genetic Diagrams II - Albino
In the following example, the result of mating between a
heterozygous albino man and another heterozygous albino woman is
studied. It is known that the
allele for normal pigment is dominant over the allele for albino.
Albino is a disease that causes people to be unable to produce
pigments and their hairs and skins are colourless as a result.
This is due to an effective gene that produces a defective
Let N be the dominant allele for normal pigment.
Let n be the recessive allele for albino.
Parent phenotype Heterozygous Normal Heterozygous Normal
Parent genotype Nn X Nn
Gametes N n N n
Possible offspring genotype NN Nn Nn nn
Offspring phenotype Normal Normal Normal Albino
Ratio of phenotype 3 normal : 1 albino
the two fruit flies are heterozygous, their homologous chromosomes has the
different alleles. When the homologous chromosomes separate during meiosis, the
each parent will produce two types of alleles, N for normal
pigment and n for albino. When
the two gametes, (one from mother and one from father), fuse during
fertilisation, three types of cells results. The ratio of normal child
to albino child is 3 : 1.
and Maternal Chromosomes