Question

Explain the phenomenon of nondisjunction that may cure during gamete meiosis, & describe some of the consequences that can arise if nondisjunction ocures for sex and non-sex chromosomes.

Answer 1

Nondisjunction is basically failure of homologous chromosomes or sister chromatids to separate properly and precisely during cell division

• All cells, except eggs and sperm cells, have two sets of 23 chromosomes, of a total of 46 chromosomes. If there are two sets of chromosomes, it is called diploid and designated as 2n.
• Eggs and sperm cells are called gametes because they have only one set of 23 chromosomes, which is called a haploid, or n.
• When one egg and one sperm cell fuse during fertilization, a diploid cell is produced. This diploid cell has one set of chromosomes from the egg and one set of chromosomes from the sperm cell. This diploid cell will divide and develop into a baby.
• If everything goes perfectly during meiosis, chromosomes will be separated and distributed evenly to produce four haploid gametes. However, sometimes chromosomes do not separate properly. This is called nondisjunction and results in gametes with either too many or too few chromosomes.

Consequences of sex and non-sex chromosomes

• Turner syndrome: Complete loss of an entire X chromosome
• Down syndrome: A trisomy of chromosome 21
• Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13)
• Klinefelter syndrome