Which of the following can result in Down Syndrome in an individual?a)...
Non-disjunction of chromosome 21 can lead to trisomy of 21 after fertilization with a haploid gamete. This results in Down Syndrome. When a part of chromosome 21 cuts off and gets translocated on chromosome 14, it gives a trisomy like effect when this 14/21 chromosome gets segregated into a gamete and is fertilized. So, both translocation and non-disjunction result in Down Syndrome.
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Which of the following can result in Down Syndrome in an individual?a)...
The correct answers are option 'A' and 'B': Non-disjunction of chromosome 21 prior to or at conception and translocation of a part of chromosome 21 to chromosome 14.
Explanation:
- Non-disjunction of chromosome 21 prior to or at conception: Non-disjunction is the failure of chromosomes to separate properly during cell division. In the case of Down Syndrome, there is a non-disjunction of chromosome 21, where both copies of chromosome 21 fail to separate during the formation of eggs or sperms. As a result, an individual ends up with an extra copy of chromosome 21, leading to the condition known as Down Syndrome.
- Translocation of a part of chromosome 21 to chromosome 14: Translocation is a genetic rearrangement where a part of one chromosome breaks off and attaches to another chromosome. In some cases, a part of chromosome 21 may break off and attach to chromosome 14. This type of translocation is called a Robertsonian translocation. If a person with a Robertsonian translocation involving chromosome 21 and 14 reproduces, there is a chance that their child may inherit the translocated chromosome, which can result in Down Syndrome.
Let's understand the other options as well:
- Paracentric inversion in chromosome 21 leading to the formation of a dicentric bridge: An inversion is a genetic rearrangement where a segment of a chromosome is flipped in orientation. A paracentric inversion refers to an inversion that does not include the centromere. In the case of Down Syndrome, a paracentric inversion in chromosome 21 would not directly result in the condition. It may lead to some other genetic abnormalities but not Down Syndrome.
- Deletion of a gene on chromosome 21: Down Syndrome is not caused by the deletion of a single gene on chromosome 21. It is the presence of an extra copy of the entire chromosome 21 that leads to the characteristic features of Down Syndrome.
In summary, the non-disjunction of chromosome 21 and translocation of a part of chromosome 21 to chromosome 14 are the two genetic events that can result in Down Syndrome. Non-disjunction leads to an extra copy of chromosome 21, while translocation can cause an individual to inherit a translocated chromosome, leading to the condition.