Question

A mother carries one allele of a recessive gene for a disease on an autosome, and the father carries no recessive alleles of the gene for that disease. What is the likelihood of their child having the disease?
A. 0%
B. 50%
C. 75%
D. 100%

Answer 1

What is the likelihood of their child having the disease is:

A. 0%

Explanation:

• The mother is  heterozygous, thus she has an allele which is recessive and the other allele which is dominant.
• The father has no recessive allele for the gene.
• During meiosis in mother , two types of gametes will be produced. One type of gamete will have the recessive allele and the other type of gametes will have dominant allele.
• During meiosis in father, only one type of gametes will be formed which will have the dominant allele only.
• In a situation a female gamete with recessive allele is fertilized by a male gamete with dominant allele. The resulting zygote will be heterozygous.The effect of the recessive allele will be masked by the dominant allele and the child will not have the disease.
• In a situation a female gamete with the dominant allele is fertilized by a male gamete with dominant allele then the resulting zygote will be homozygous  for dominant allele and obvioiusly the individual will not have the disease.
• Thus, in this case we can conclude that there is 0% chance of child having the disease.