Colour blindness is a sex-linked recessive disorder. Let the recessive allele be .

1. Female Genotype: Since she is colour blind, she must be homozygous recessive: .
2. Male Genotype: The man has a colour blind mother (). Males receive their X chromosome from their mother. Therefore, he received from her. His genotype is (he is also colour blind).
3. The Cross: (Female) (Male).
4. Progeny:

• Daughters receive from mother and from father (Colour blind).
• Sons receive from mother and from father (Colour blind). Since all offspring are affected, the chance is 100% .