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

Question: Explain how nondisjunction in female gametes can lead to Klinefelter and Turner syndrome in human offspring after being fertilized by a normal male gamete. Answer: Nondisjunction in female gametes can lead to Klinefelter and Turner syndrome when fertilized by a normal male gamete. For Klinefelter syndrome, a female gamete undergoes nondisjunction and retains an extra X chromosome (XX), and when fertilized by a male gamete carrying a Y chromosome, the offspring has an abnormal chromosomal pattern (47, XXY). For Turner syndrome, a female gamete undergoes nondisjunction and has a missing X chromosome (0X), and when fertilized by a male gamete carrying an X chromosome, the offspring has an abnormal chromosomal pattern (45, X).

Step-by-step solution

Understanding nondisjunction

Nondisjunction is an error that occurs during meiosis, the process by which gametes (eggs and sperm) are formed. It happens when chromosomes fail to separate properly during the formation of the gametes, which leads to gametes having an abnormal number of chromosomes. In the case of human female gametes, the typical number of chromosomes should be 23, but due to nondisjunction, it can end up having either 22 or 24 chromosomes.

Klinefelter Syndrome

Klinefelter syndrome results from the presence of an extra X chromosome, giving an abnormal chromosomal pattern of 47, XXY. Under normal circumstances, female gametes have one X chromosome and male gametes have either an X or a Y chromosome. Thus, during fertilization, a normal male gamete with an X chromosome would result in XX (female) offspring, while a normal male gamete with a Y chromosome would result in XY (male) offspring.

Formation of Klinefelter Syndrome due to Nondisjunction

The development of Klinefelter syndrome occurs through the following process: 1. Nondisjunction occurs during the formation of a female gamete, causing it to have 24 chromosomes instead of the normal 23. This includes an extra X chromosome, leading to a chromosomal pattern of XX in the female gamete. 2. The abnormal XX female gamete is fertilized by a normal male gamete carrying a Y chromosome. 3. The resulting zygote has a chromosomal pattern of 47, XXY, leading to Klinefelter syndrome.

Turner Syndrome

Turner syndrome results from the presence of a single X chromosome, giving an abnormal chromosomal pattern of 45, X. This syndrome occurs in females, where one of the X chromosomes in a pair is missing or has been altered.

Formation of Turner Syndrome due to Nondisjunction

The development of Turner syndrome occurs through the following process: 1. Nondisjunction occurs during the formation of a female gamete, causing it to have 22 chromosomes instead of the normal 23. This includes the absence of an X chromosome, leading to a chromosomal pattern of 0X in the female gamete. 2. The abnormal 0X female gamete is fertilized by a normal male gamete carrying an X chromosome. 3. The resulting zygote has a chromosomal pattern of 45, X, leading to Turner syndrome. In conclusion, nondisjunction in female gametes can lead to Klinefelter and Turner syndrome in offspring when fertilized by a normal male gamete.