You are presented with a patient named Gerry who has Down sy

You are presented with a patient, named Gerry, who has Down syndrome (trisomy 21). You determine the nondisjunction event occurred in his mother, named Mary, during meiosis I. The TPTE gene is on chromosome 21. Mary has two different alleles of the TPTE gene (ex. T and t). Do Gerry\'s maternally-inherited chromosome 21s have the same or different alleles of the TPTE gene? Do not worry about recombination in this question. Same alleles Different alleles Not enough information to determine the answer

Solution

A. Different allele

Gerry\'s maternally inherited 21st chromosome will have the different allele. This is because, non disjuction has occured during meioisis I. This means 21st homologous chromosome have failed to separate. During meiosis II both the homologs willhave separated so egghavereceived one copy of chromatid from each chromosome. Therefore Gerry will receive different alleles from maternal 21st chromosome.