Question

question 5
1 pts
what is the source of the extra chromosome 21 in an individual with down syndrome?

nondisjunction in the mother only
nondisjunction in the father only
duplication of the chromosome
nondisjunction in either parent

Explanation:

Down syndrome is usually caused by trisomy 21. Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. It can occur in either parent (mother or father) during gamete formation (meiosis). If nondisjunction happens during meiosis in the mother or father, the resulting gamete can have an extra chromosome 21. When this gamete fuses with a normal gamete during fertilization, the zygote will have three copies of chromosome 21 (trisomy 21). Duplication of the chromosome is not the typical mechanism for the extra chromosome 21 in Down syndrome. It's not limited to only the mother or only the father as nondisjunction can occur in either.

Answer:

nondisjunction in either parent