Question

Aneuploidy may occur in some cells of an individual if nondisjunction happens in

A. an early embryo.
B. a sperm cell.
C. an oocyte.
D. a polar body.

Answer 1

Aneuploidy results from nondisjunction during meiosis in germ cells or during early embryonic development. It leads to gametes or cells with abnormal chromosome numbers, which may result in an aneuploid zygote if it affects gametes or a mosaic of aneuploid and normal cells if it occurs in an early embryo.

Step-by-step explanation:

Aneuploidy can occur in an individual if nondisjunction happens in multiple stages: during the early embryonic stage, in a sperm cell, in an oocyte, or even in a polar body. However, aneuploidy will have the potential to affect the resulting organism if it occurs in a gamete that participates in fertilization (sperm or oocyte) or during an early embryonic division. Nondisjunction during these critical points can result in gametes possessing an abnormal number of chromosomes - specifically, either one extra (n+1) or one less (n-1) than the usual number.

During meiosis I, nondisjunction involves the failure of homologous chromosomes to separate, while during meiosis II, it involves the failure of sister chromatids to separate. If nondisjunction occurs in a germ cell (sperm or oocyte), the resulting gametes can form an aneuploid zygote upon fertilization. If it occurs in an early embryo, it leads to a mosaic pattern of normal and aneuploid cells within the same individual.

In the specific examples given:

1. Nondisjunction in an early embryo results in a mixture of normal and aneuploid cells, potentially leading to an individual with a mosaic aneuploidy condition.
2. Nondisjunction in a sperm cell or oocyte leads to aneuploid gametes that, if participating in fertilization, can lead to an aneuploid zygote and subsequently an aneuploid organism.
3. Nondisjunction in a polar body, typically does not affect the resulting offspring since polar bodies do not contribute to the genetic material of the embryo.