Question

Describe the maternal age effect associated with down syndrome

Answer 1

Answer:

In every cell in the human body there is a nucleus, where genetic material is stored in genes. Genes carry the codes responsible for all of our inherited traits and are grouped along rod-like structures called chromosomes. Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21.

Down's syndrome is a chromosomal disorder caused by the presence of an extra 21st chromosome. It is referred to as trisomy 21.

Individuals with Down syndrome tend to have a lower-than-average cognitive ability, often ranging from mild to moderate disabilities. A small number have severe to profound mental disability.

Reason- This disorder is due to the non disjunction of chromosomes during the meosis II,

which results in the failure of sister chromatids to separate during meosis II.

This results imbalance of chromosomes in the cell and such a cell is called aneuploid.

Loss of a single chromosome (2n-1), in which the daughter cell(s) with the defect will have one chromosome missing from one of its pairs, is referred to as a monosomy.

Gaining a single chromosome, in which the daughter cell(s) with the defect will have one chromosome in addition to its pairs and is referred to as a trisomy.

                

The most common risk factor for Down syndrome is maternal age. As a woman gets older, her risk to have a pregnancy with a chromosome abnormality increases.

The rate of aneuploidy is higher in oocytes than in spermatocytes. Most of non disjunction errors occur in meosis I of oocytes, and the prolonged arrest of meosis-I is responsible for these errors.