Question

why do some people have unusual chromosome combinations, such as xyy and xxx?
people who inherit large numbers of short tandem repeats (strs) also inherit extra sex chromosomes.
errors occurred in chromosome segregation during meiosis in their fathers or mothers.
it is not known why these unusual chromosome combinations occur.
genetic disease causes a spontaneous increase in the number of sex chromosomes in mature gametes.
a mistake in mitosis during embryonic development leads to extra sex chromosomes in every cell.

Explanation:

During meiosis (cell division to form gametes), errors in chromosome segregation (like non - disjunction) can lead to gametes with extra chromosomes. For example, in the case of XYY, an error in sperm formation (meiosis in father) could lead to a sperm with two Y chromosomes. In XXX, an error in egg (meiosis in mother) or sperm formation could lead to an extra X - bearing gamete. Short tandem repeats (STRs) are repetitive DNA sequences and not directly related to extra sex chromosomes. It is known that meiotic errors cause these, so option C is wrong. Genetic diseases don't "cause" a spontaneous increase in sex chromosomes in this way; it's a meiotic error. Mitosis (for growth and repair in embryos) errors would lead to mosaicism (not all cells affected), not all cells having extra sex chromosomes as in the question.

Answer:

B. Errors occurred in chromosome segregation during meiosis in their fathers or mothers.