OBJECTIVE LIFE SCIENCE
GENETICS
|
Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
|
|
|
Incomplete dominance
|
|
|
Nondisjunction
|
|
|
Inversion mutation
|
|
|
Substitution mutation
|
Detailed explanation-1: -About 95 percent of the time, Down syndrome is caused by trisomy 21-the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell.
Detailed explanation-2: -WHY MARCH 21? The date for WDSD being the 21st day of the 3rd month, was selected to signify the uniqueness of the triplication (trisomy) of the 21st chromosome which causes Down syndrome. WHAT IS DOWN SYNDROME? Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21.
Detailed explanation-3: -Parents with one baby with regular trisomy 21 are usually told that the chance of having another baby with Down’s syndrome is 1 in 100. Very few families are known who have more than one child with Down’s syndrome, so the real chance is probably less than this.