Question

5. A man homozygous for a rare recessive disorder (a/a) marries a normal woman (A/A) If nondisjunction occurs in the male in meiosis I what will the gametes look like? a. b. What about if it happens in meiosis lI? 6. A man heterozygous for a rare recessive disorder (A/a) marries a normal woman (A/A) Their first child is trisomic (A/a/a) In which parent and at what stage of meiosis did nondisjunction occur? a. What kind of euploidy is this an example of? b.

Answer 1

Answer 5:

attatta disjunchion

If non disjunction at meiosis one then two gametes carry two copies of chromosomes and two gametes are empty.

attatta

If non disjunction occur at meiosis two, then two normal gametes and one gamete with two copies of chromosomes and one gamete is empty.

Answer 6: first child has trisomy A aa. This child has a allele contributed from the father, because mother lack this allele. Mother is homozygous for A allele. So mother contributed A allele in first child. Now a allele contributed from father. This a allele is non disjunction at meiosis two stage. If non disjunction occur at meiosis one, then the child received Aa allele from the father. The genotype of child will be AAa.

First child genotype:AAa is example of aneuploidy trisomy. Aneuploidy: abnormal chromosome number.

Trisomy: person have three chromosome instead of two copies.