A boy with Klinefelter syndrome (47,XXY) is born to a mother who is phenotypically normal and a father who has the X-linked skin condition called anhidrotic ectodermal dysplasia. The mother's skin is completely normal with no signs of the skin abnormality. In contrast, her son has patches of normal skin and patches of abnormal skin. Using the appropriate genetic terminology, describe the meiotic mistake that occurred. Be sure to indicate in which division the mistake occurred.

Key Concepts

Klinefelter Syndrome

Klinefelter syndrome is a genetic condition in males characterized by the presence of an extra X chromosome, resulting in a 47,XXY karyotype. This condition can lead to various physical and developmental features, including infertility, reduced testosterone levels, and sometimes learning difficulties. It arises from nondisjunction during meiosis, where chromosomes fail to separate properly, leading to gametes with an abnormal number of chromosomes.

Nondisjunction

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division, specifically during meiosis I or meiosis II. This error can result in gametes with an abnormal number of chromosomes, which, when fertilized, can lead to conditions like Klinefelter syndrome. In this case, the meiotic mistake likely occurred during meiosis I, where the X and Y chromosomes did not segregate correctly.

X-linked Inheritance

X-linked inheritance refers to the pattern of inheritance for genes located on the X chromosome. Conditions that are X-linked, such as anhidrotic ectodermal dysplasia, are typically expressed in males who have only one X chromosome. Females, having two X chromosomes, may be carriers without showing symptoms. In this scenario, the father’s X-linked condition does not affect the mother, who is phenotypically normal, but can be passed to male offspring if the mother is a carrier.