Question

Describe how nondisjunction in human female gametes can give rise to Klinefelter and Turner syndrome offspring following fertilization by a normal male gamete.

Short answer

Answer: Nondisjunction in human female gametes can result in offspring with Klinefelter syndrome (XXY) or Turner syndrome (X0), due to an abnormal number of sex chromosomes in the zygote. Klinefelter syndrome, which affects males, presents symptoms such as reduced fertility and small testicles, while Turner syndrome affects females with features like short stature and infertility.

Step-by-step solution

Understanding nondisjunction

Nondisjunction is an error in meiosis, the process that creates gametes (egg and sperm cells). During meiosis, the chromosomes should separate properly, resulting in gametes with the right number of chromosomes. However, in nondisjunction, chromosomes fail to separate correctly, producing gametes with an abnormal number of chromosomes. In this exercise, we'll focus on nondisjunction in human female gametes (egg cells).

Normal chromosome distribution

In humans, each cell contains 46 chromosomes in 23 pairs. One chromosome of each pair is inherited from the mother, and the other from the father. Sex chromosomes determine an individual's sex: females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). During normal meiosis in females, each egg cell should receive one X chromosome.

Nondisjunction in human female gametes

In the case of nondisjunction, an error occurs during meiosis in the egg cell formation. The X chromosomes fail to separate properly, leading to egg cells with either two X chromosomes or no X chromosome instead of just one.

Fertilization with normal male gamete

A normal male gamete contains either an X or a Y chromosome. When a male gamete (sperm) with an X chromosome fertilizes an egg cell with two X chromosomes (due to nondisjunction), the resulting zygote will have three sex chromosomes (XXY). This condition is known as Klinefelter syndrome. On the other hand, if a male gamete with a Y chromosome fertilizes an egg cell without an X chromosome (also due to nondisjunction), the resulting zygote will have only one sex chromosome (X0). This condition is called Turner syndrome.

Klinefelter syndrome and Turner syndrome offspring

The offspring resulting from the aforementioned cases of nondisjunction will have the Klinefelter or Turner syndrome. Klinefelter syndrome (XXY) affects males, causing symptoms like reduced fertility, small testicles, and enlarged breast tissue. Turner syndrome (X0) affects females and is characterized by short stature, infertility, and heart defects, among other features. In summary, nondisjunction in human female gametes can give rise to Klinefelter and Turner syndrome offspring when these abnormal egg cells are fertilized by a normal male gamete. This is because the chromosomes fail to separate properly during meiosis, which leads to zygotes with an unusual number of sex chromosomes.