Question

Betsy has an autosomal recessive disorder. Kevin is a carrier. They have one boy (II-3) who has the same autosomal recessive disorder as his mom.

On the gel, thick bands represent twice as much DNA as thin bands (kb = kilobases = length). Betsy is homozygous for the 4-kb mutant allele. Kevin is heterozygous for the 4-kb mutant allele and the 15-kb normal allele.

4 15/4 F-1 12 M 2 IM || 2 -3

Which of the following situations could explain the genotype of their first son (II-2)?

• A. Normal meiosis/fertilization, one allele from Kevin and one allele from Betsy
• B. Abnormal meiosis, both the child's alleles come from Kevin, none from Betsy
• C. Abnormal meiosis, both the child's aleles come from Betsy, none from Kevin

Answer 1

Option - b.abnornal meiosis both the childs allele come from kevin and none from betsy

Explanation

From the information given, Betsy has autosomal recessive disorder i.e ss genotype and Kevin with normal but have one dominant and one recessive heterozygous allele i.e Ss

The allele s represent 4kb on gel and allele S represent 15kb on gel. In the child II -2 , the gel image represents the band only on 15kb and not 4kb hence the child II-2 have only SS genotype. S allele is present in only kevin and not Betsy, hence child have both allele from kevin and none from betsy.