73. If nondisjunction of a chromosome occurs in meiosis II, what will be the product at the completion of
meiosis?
(1) All the gametes will be diploid
(2) Two gametes will be n + 1, and two will be n – 1
(3) One gamete will be n + 1, one will be n – 1, and two will be n
(4) Two of the four gametes will be haploid, and two will be diploid

Introduction:

Meiosis is the fundamental process by which gametes (sperm and egg cells) are produced. This process ensures that each gamete has half the number of chromosomes as the parent cell. However, errors during meiosis, such as nondisjunction, can disrupt this delicate process and result in abnormal gametes.

In this article, we will explore the effects of nondisjunction in meiosis II and how it affects the genetic makeup of the resulting gametes.

What is Nondisjunction in Meiosis II?

Nondisjunction occurs when chromosomes do not separate properly during cell division. While meiosis I involves the separation of homologous chromosomes, meiosis II is where sister chromatids are supposed to be separated into two different cells. If nondisjunction happens during meiosis II, the chromatids fail to separate, leading to gametes with abnormal chromosome numbers.

Outcome of Nondisjunction in Meiosis II

The result of nondisjunction in meiosis II is that two gametes will receive an extra chromosome (n + 1), while two gametes will be missing a chromosome (n – 1). This produces a total of four gametes with the following genetic composition:

1. Two gametes with one extra chromosome (n + 1).

2. Two gametes with one missing chromosome (n – 1).

3. Two gametes with the normal chromosome number (n).

Correct Answer:

The correct outcome of nondisjunction in meiosis II is:

(3) One gamete will be n + 1, one will be n – 1, and two will be n.

This option reflects the typical genetic consequences of nondisjunction, where one gamete gains an extra chromosome, another loses a chromosome, and the remaining two gametes have the correct chromosome count.

Consequences of Nondisjunction:

1. Monosomy and Trisomy: The gametes with n + 1 or n – 1 chromosome counts can lead to monosomy (missing one chromosome) or trisomy (extra chromosome) in the offspring. For instance, if a gamete with n + 1 chromosomes fuses with a normal gamete, it can result in a trisomic individual with three copies of a chromosome.

2. Genetic Disorders: Conditions such as Down syndrome (trisomy 21) and Turner syndrome (monosomy X) are examples of genetic disorders caused by nondisjunction in meiosis.

Conclusion:

Nondisjunction in meiosis II can lead to gametes with abnormal chromosome numbers, which may have significant genetic consequences in the offspring. By understanding this process, we can better appreciate the complexities of genetic inheritance and the potential for errors in the process of gamete formation.