AP BIOLOGY

Detailed explanation-1: -Nondisjunction is the failure of homologous chromosomes to disjoin correctly during meiosis. This results in the production of gametes containing a greater or lesser chromosomal amount than normal ones. Consequently the individual may develop a trisomal or monosomal syndrome.

Detailed explanation-2: -Nondisjunction occurs when chromosomes fail to segregate during meiosis; when this happens, gametes with an abnormal number of chromosomes are produced. The clinical significance is high: nondisjunction is the leading cause of pregnancy loss and birth defects.

Detailed explanation-3: -Nondisjunction Examples Nondisjunction causes abnormal number chromosomes in all the cells called aneuploidy or in some cells called mosaicism. Some of the important examples are: Down’s syndrome – Trisomy of autosomes, i.e. chromosome 21. It contains one extra chromosome 21.

Detailed explanation-4: -Nondisjunction in meiosis can result in pregnancy loss or birth of a child with an extra chromosome in all cells, whereas nondisjunction in mitosis will result in mosaicism with two or more cell lines. Aneuploidy may also result from anaphase lag.