Question

Which of the following offspring genotypes could result from the fertilization of an egg that had undergone nondisjunction in meiosis II with a normal haploid sperm? (Because a nondisjunction event in meiosis II could involve the chromosome containing gene A or the chromosome containing gene a, be sure to consider both possibilities in your final answer .)

Answer 1

Answer:

 AAa, aaa, Aa, aa or a.

Explanation:

The phenomenon where homologous chromosome failed to separate into new daughter cells , but remained joined together  so that one daughter cell  has extra number of chromosomes while the other daughter cell has empty chromosome in nucleus is called non dis junction.

In this present scenario   in the mother with heterozygous  gene (Aa) , during oogenesis at anaphase of meiosis 1. each of the gene  separate, and move to the different  oocytes -daughter cells .

However, at meiosis 2, instead of the each chromosomes to undergo centromere separation at metaphase  ii ,either of A  or a -genes, may failed to do this and rather migrates into  same  oocyte -daughter cells. Because this is a random events, the oocyte may have;

 AA/aa,-assuming one A or  a failed to separate and joined with another,

or

A  /a. assuming no  extra to pair  because of  extra copies in some oocytes

or  

(0)-nothing.-assuming extra copies has prevented equal distribution in non-dijuction oocytes.

if  either of these cells above  is fertilized by  haploid sperm of father with homozygote recessive gene a  in random fertilisation; the haploid  sperm with  gene a  after fertilization produce either of offspring  of the following chromosomes combinations;

as a result   of non-dis-joined zygotes  AAa, aaa, Aa, aa or a.

Answer 2

Answer:

See explanation below

Explanation:

Non-disjunction occur as a result of lack of separation of homologous chromosomes during meiosis.

As a result, the gametes (the daughter cells formed) produced end up having extra or lesser chromosomes as compared to a normal gamete.

When a gamete with extra chromosome fertilizes a normal gamete, the resulting offspring will have an extra chromosome (trisomy condition).

On the other hand, when a gamete with one less chromosome than normal fertilizes a normal gamete, the resulting offspring will have one less chromosome than normal offspring (monosomy condition).

Assuming a chromosome with Aa gene undergoes non disjunction during meiosis, the resulting gametes either contain both A and a chromosome or contain no chromosome at all.

If Aa gamete is fertilized by a normal haploid sperm (a), the resulting zygote will have the genotype Aaa.

If a gamete with no chromosome at all fertilizes a normal haploid sperm, the resulting offspring will have the genotype a.