AP BIOLOGY

Detailed explanation-1: -Nondisjunction in meiosis II results from the failure of the sister chromatids to separate during anaphase II.

Detailed explanation-2: -Disorders of chromosome number include the duplication or loss of entire chromosomes, as well as changes in the number of complete sets of chromosomes. They are caused by nondisjunction, which occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis.

Detailed explanation-3: -Normally, meiosis causes each parent to give 23 chromosomes to a pregnancy. When a sperm fertilizes an egg, the union leads to a baby with 46 chromosomes. But if meiosis doesn’t happen normally, a baby may have an extra chromosome (trisomy), or have a missing chromosome (monosomy).

Detailed explanation-4: -Trisomy is the presence of an extra chromosome. This can arise as a result of non-disjunction, when homologous chromosomes fail to separate at meiosis resulting in a germ cell containing 24 chromosomes rather than 23.

Detailed explanation-5: -One cause of aneuploidy is nondisjunction during meiosis (E-Fig. 1-31), resulting in either extra chromosomes (e.g., trisomy, tetrasomy) or one less chromosome (i.e., monosomy) (see E-Fig. 1-31).