What are non-disjunction and its consequences in meiosis?

Non-disjunction is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis. Its consequences include genetic disorders.

Non-disjunction is a crucial concept in genetics, occurring during the process of meiosis, which is the type of cell division that produces gametes (sex cells) for sexual reproduction. In a normal meiosis, homologous chromosomes (one from each parent) pair up and then separate, ensuring that each gamete receives one copy of each chromosome. However, in non-disjunction, this separation does not occur correctly. This can happen in either the first or second division of meiosis. In the first case, both members of a homologous pair go into the same daughter cell. In the second case, the sister chromatids fail to separate and both daughter chromosomes go into the same gamete.

The consequences of non-disjunction can be severe, as it results in gametes with an incorrect number of chromosomes. When these gametes are involved in fertilisation, they can lead to offspring with a wrong number of chromosomes, a condition known as aneuploidy. This can cause a variety of genetic disorders, depending on which chromosomes are affected.

For example, Down's syndrome is caused by an extra copy of chromosome 21, resulting from non-disjunction. Similarly, Klinefelter's syndrome (in males) and Turner's syndrome (in females) are caused by non-disjunction of the sex chromosomes. These conditions can have a range of effects on the individual's physical and mental development, and in some cases, can be life-threatening.

In conclusion, non-disjunction is a significant error in meiosis that can lead to serious genetic disorders. Understanding this process is crucial for understanding how these conditions occur and how they might be prevented or treated.