Question

A man can inherit his X-chromosome from his-
A. Maternal grandfather or maternal grandmother.
B. Father.
C. Maternal grandfather.
D. Paternal grandfather.
E. Paternal grandmother.

Answer 1

By performing a test cross, we can determine whether the individual is homozygous or heterozygous dominant. In a test cross, an individual bred with another individual that is homozygous for the recessive trait and offspring of the test cross is determined. This test has two possibilities- if any offspring produced express the recessive trait, the individual is heterozygous for the dominant allele.

Complete answer:
Option A Maternal grandfather or maternal grandmother- A man or male have both XY chromosomes unlike females who have both XX chromosomes. So, a man can inherit his X chromosome either from his maternal grandfather or maternal grandmother, as men are heterozygous. And Y cannot carry any genes.
So, option A is correct
Option B Father- father is a male too so he got the chromosomes XY and as a male has XY chromosomes so biologically it is not possible. As males are heterozygous.
Option B is not correct.
Option C Maternal grandfather- as the genes are heterozygous for a male and homozygous in females so, maternal grandfather can contribute genes.
So, option C is not correct.
Option D Paternal grandfather- biologically, the male child possesses the X chromosome from their mother and the X chromosome is typically three times larger than Y chromosome.
So, option D is not correct.
Option E paternal grandmother- as we already knew that the X is inherited from the maternal grandfather or grandmother not the paternal grandmother.
So, option E is not correct.

Hence, Option A is the correct answer.

Note:
As we know that Each organism carries two copies of each trait- one was dominant trait and one is recessive. A girl child is born taking one X chromosome from mother and another X chromosome from her father. And males are born from X from mother and Y from father. In females there are two XX chromosomes in which one remains always inactivated. X is bigger than Y chromosome. Together they are called sex chromosomes.