Question

Which one is the likely cause of tetraploidy in man?

	A.	lack of cytokinesis following the first mitosis after fertilization
	B.	fertilization of the egg by an aneuploid (1n + 1) sperm
	C.	a normal sperm fertilizes a diploid egg
	D.	a Robertsonian translocation must have occurred in the egg
	E.	nondisjuction during first mitosis after fertilization

Answer 1

Answer :

Correct choice is E

Normal human ploidy is 2n.

Gametes will be n haploid.

Cytokinesis is a part of cell division in which cytoplasm separates into two. If this is not happening the resulting cell will have 2 nucleus. That is 2 copies of a chromosome in each nucleus. After first mitosis following fertilization.

Fertilization of an egg n with aneuploid sperm result in one more extra chromosome 2n + 1.

When normal sperm fertilizes diploid egg 2n + n result in triploid zygote. 3n

In Robertsonian translocation one chromosome get attached to another. Ploidy will not change to quadraploid.

In non disjunction sister chromatids wont separate during cell division. This mostly results in aneuploidy or tetraploidy.