AP BIOLOGY

Detailed explanation-1: -Nondisjunction in meiosis II results from the failure of the sister chromatids to separate during anaphase II. Since meiosis I proceeded without error, 2 of the 4 daughter cells will have a normal complement of 23 chromosomes. The other 2 daughter cells will be aneuploid, one with n+1 and the other with n-1.

Detailed explanation-2: -If sister chromatids fail to separate during meiosis II, the result is one gamete that lacks that chromosome, two normal gametes with one copy of the chromosome, and one gamete with two copies of the chromosome. Figure 7.8 Following meiosis, each gamete has one copy of each chromosome.

Detailed explanation-3: -If nondisjunction occurs in meiosis II, two of the four products will be unaffected by the event and two of the products will be abnormal. One abnormal product will have an extra chromosome, and the other abnormal product will be missing that chromosome.

Detailed explanation-4: -Nondisjunction, in which chromosomes fail to separate equally, can occur in meiosis I (first row), meiosis II (second row), and mitosis (third row). These unequal separations can produce daughter cells with unexpected chromosome numbers, called aneuploids.

Detailed explanation-5: -They are caused by nondisjunction, which occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis. The risk of nondisjunction increases with the age of the parents. Nondisjunction can occur during either meiosis I or II, with different results (Figure 7.8).