Question

Being euploid does not necessarily mean that the chromosomes are complete. Pick a disease that results from a chromosomal abnormality and describe the characteristics of the disease, the type of abnormality that occurs, and the chromosome number and section that is abnormal.

Answer 1

Ans) Numerical disorders occur when there is a change in the number of chromosomes (more or fewer than 46). Examples of numerical disorders include trisomy, monosomy and triploidy. Some examples of more common chromosome deletion syndromes include cri-du-chat syndrome and 22q11.2 deletion syndrome.

- Trisomy 21 nondisjunction?
This type of Down syndrome, which accounts for 95% of cases, is called trisomy 21.
Down syndrome is usually caused by an error in cell division called "nondisjunction."
Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two.
Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate.
As the embryo develops, the extra chromosome is replicated in every cell of the body.

- Regardless of the type of Down syndrome a person may have, all people with Down syndrome have an extra, critical portion of chromosome 21 present in all or some of their cells.
This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome.
The cause of nondisjunction is currently unknown, but research has shown that it increases in frequency as a woman ages. However, due to higher birth rates in younger women, 80% of children with Down syndrome are born to women under 35 years of age.
There is no definitive scientific research that indicates that Down syndrome is caused by environmental factors or the parents' activities before or during pregnancy.
The additional partial or full copy of the 21st chromosome which causes Down syndrome can originate from either the father or the mother. Approximately 5% of the cases have been traced to the father.