During gametogenesis in a diploid organism, non-disjunction of a homologous chromosome pai… — State PSC Exam

During gametogenesis in a diploid organism, non-disjunction of a homologous chromosome pair occurs during Anaphase I of meiosis. Assuming normal segregation in Meiosis II, which of the following chromosome distributions will be observed in the four resulting gametes?

A
Two gametes with $n$ chromosomes, one gamete with $n + 1$ chromosomes, and one gamete with $n - 1$ chromosomes
Two gametes with $n + 1$ chromosomes and two gametes with $n - 1$ chromosomesAnswer
C
Four gametes, each containing a complete diploid set of $2n$ chromosomes
D
Four normal haploid gametes, each containing exactly $n$ chromosomes

Answer

Two gametes with

n + 1

chromosomes and two gametes with

n - 1

chromosomes

When non-disjunction takes place in Anaphase I of meiosis, the failure of homologous chromosomes to segregate properly yields one daughter cell with an extra chromosome and another daughter cell missing that chromosome. When these cells undergo normal Meiosis II, the resulting four gametes consist of two

(n + 1)

gametes and two

(n - 1)

gametes, leading to complete aneuploidy among all four products.

Step-by-Step Solution

Analyze the meiotic stage and event specified in the scenario

Non-disjunction occurs at Anaphase I, meaning a homologous chromosome pair fails to separate to opposite poles.

Meiosis I is the reductional division where homologous pairs segregate.

Determine the chromosomal content of the two intermediate secondary gametocytes after Meiosis I

One secondary cell receives both homologous chromosomes (an extra chromosome,

n + 1

), while the other cell receives neither (lacking a chromosome,

n - 1

The entire pair moves to one daughter cell instead of dividing equally.

Trace the chromosome distribution through normal Meiosis II equational division

The

(n + 1)

cell divides sister chromatids into two

(n + 1)

gametes, and the

(n - 1)

cell divides into two

(n - 1)

gametes.

Meiosis II separates sister chromatids normally, generating two

(n + 1)

and two

(n - 1)

gametes from the four total products.

Key Concept

Meiotic Non-Disjunction and Aneuploidy Formation

Estimated Time:1m 0s

Question

Answer

Step-by-Step Solution

Key Concept

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