Question

Explain how non-disjunction in meiosis can result in chromosome abnormalities (e.g. Down's Syndrome). Explain the effect of parental age on incidence of chromosomal abnormalities arising from non-disjunction.

Answer 1

Chromosomal nondisjunction during meiosis can result in chromosome abnormalities, such as Down's Syndrome. Parental age can also affect the incidence of chromosomal abnormalities arising from non-disjunction.

Step-by-step explanation:

Chromosomal nondisjunction during meiosis can result in chromosome abnormalities, such as Down's Syndrome. Nondisjunction occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis. This can lead to an abnormal number of chromosomes in gametes, which, if fertilized, can result in a zygote with an incorrect number of chromosomes. Down's Syndrome, for example, is caused by having three copies of chromosome 21 (trisomy 21) instead of the normal two copies.

The frequency of nondisjunction events appears to increase with parental age. The risk of bearing a child with Down's Syndrome increases in women over 36. This is because the likelihood of nondisjunction occurring in eggs increases with age. The age of the father matters less because nondisjunction is much less likely to occur in sperm. Therefore, parental age can affect the incidence of chromosomal abnormalities arising from non-disjunction.