Question

homework - genetic disorders
the karyotype of a human female is shown below.
which statement correctly explains the circumstances under which this condition happens in a cell?
○ lack of a homologous x chromosome in one of the individuals parents
○ deletion of some pieces of a sex chromosome during meiosis
○ degeneration of the x chromosome during the process of cell division.
○ nondisjunction of sex chromosomes during the process of gamete formation

Explanation:

• Lack of a homologous X chromosome in one of the individual's parents: This is not the cause. Both parents contribute to the chromosome set, and it's not about lack of a homologous X in a parent but an error in gamete formation.
• Deletion of some pieces of a sex chromosome during meiosis: Deletion would lead to a change in chromosome structure (missing parts), but here we have an extra \(Y\) (in a female - which is abnormal). A deletion is not the cause of having an extra chromosome.
• Degeneration of the X chromosome during the process of cell division: Degeneration would lead to loss of function of the \(X\) chromosome, not an extra \(Y\) chromosome.
• Nondisjunction of sex chromosomes during the process of gamete formation: Nondisjunction is when chromosomes fail to separate properly during meiosis (gamete formation). In this case, if there was a nondisjunction in the formation of either the sperm (which can carry \(X\) or \(Y\)) or egg (which normally carries \(X\)), an abnormal gamete with an extra \(Y\) could be produced. When this abnormal gamete fuses with a normal gamete (carrying \(X\)), an individual with an abnormal karyotype (like having \(X\) and \(Y\) in a female - which is not the normal \(XX\)) is formed.

Answer:

nondisjunction of sex chromosomes during the process of gamete formation