Question

Fruit flies have 4 chromosomes per set. A diploid fly with monosomy 3 has _________ chromosomes.

Select one:

a. 4

b. 3

c. 5

d. 8

e. 9

f. 7

Answer 1

Ans.

The answer is (f). 7

Explanation:

When an abnormal number of chromosomes are present in a cell it is reffered as Aneuploidy. Monosomy is a type of aneuploidy where the total number of chromosomes are not in an exact multiple of sets.That is, only one chromosome from a set is present and the other being absent.Monosomy 3 or chromosome 3 is a chromosomal disorder where the end portion of chromosome 3 is absent.

Thus,for a diploid cell having two sets of chromosomes, the number of chromosomes per set is given by 2N, but in monosomy it will 2N-1, where N= number of chromosomes per set.

Now, a diploid fly will be having 2N=2x4= 8 Chromosomes. ( 2 sets of 4 Chromosome each)

and therefore a diploid fly with monosomy 3 will be having 2N-1=8-1 = 7 Chromosomes.

Hence, the answer is 7 chromosomes.