Colour blindness is a recessive disorder. If a colour blind male is crossed with a normal female, what are the possible genotypes and phenotypes of the offspring
To determine the possible genotypes and phenotypes of the offspring in a cross between a colour blind male and a normal female, we need to consider the inheritance pattern of colour blindness.
Colour blindness is caused by a mutation on the X chromosome. Since males have one X and one Y chromosome (XY), they inherit their X chromosome from their mother. On the other hand, females have two X chromosomes (XX) and inherit one from each parent.
Let's denote the alleles for colour blindness as "C" for the normal allele and "c" for the recessive colour blindness allele.
In this case, the male is colour blind, so his genotype is "XcY," meaning he has one normal X chromosome and one colour blind X chromosome.
The female is normal, so her genotype is "XCX," meaning she has two normal X chromosomes.
Now, let's consider the possible genotypes and phenotypes of their offspring:
1. Female offspring (XX): If the male parent passes on the "Y" chromosome, the female offspring will inherit one normal X chromosome from the father and one normal X chromosome from the mother. In this case, all the female offspring will be phenotypically normal (not colour blind) because they have two normal X chromosomes.
2. Male offspring (XY): If the male parent passes on the "X" chromosome with the colour blindness allele, the male offspring will inherit one normal X chromosome from the mother and one colour blind X chromosome from the father. In this case, the male offspring will be colour blind because they have only one X chromosome, and the mutation for colour blindness is present on that X chromosome.
To summarize:
- All the female offspring will be phenotypically normal because they have two normal X chromosomes (XX).
- Half of the male offspring will be colour blind because they have one normal X chromosome and one colour blind X chromosome (XY), inheriting the colour blindness allele from their father.
So, the possible genotypes and phenotypes of the offspring in this cross are:
- Female offspring: Genotype XX, Phenotype Normal
- Male offspring: Genotype XY, Phenotype Colour blind