An Rh-negative woman is married to an Rh-positive man whose father was also Rh-negative. What are the chances that their child will have Rh negative blood group?
Correct answer: B. 50%
- A. 25%
- B. 50%
- C. 75%
- D. 100%
Explanation
Given that the man's father was Rh-negative and the man is Rh-positive, the man must be heterozygous for Rh-positive. A negative woman should be homozygous as a recessive allele only expresses itself in homozygous conditions. When a heterozygous dominant individual is crossed with a homozygous recessive individual, the offspring show the dominant and recessive phenotypes in a ratio of 1:1. Hence, there is a fifty percent chance of their child being "affected" with Rh negative phenotype.
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About Inheritance
Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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