Question

A colour blind man ($X^CY$) marries a woman who is carrier for haemophilia ($XX^h$). Which of the following is true for their progenies?
A. $25\%$ progenies carry the genes for both haemophilia and colour blindness.
B. $25\%$ male progenies carry only the gene for haemophilia.
C. $25\%$ female progenies carry only the gene for colour blindness.
D. All of these

Answer 1

An illness caused by changes in the genetic material or DNA of the person is termed as genetic disorder. There are two types of genetic disorders- mendelian disorders and chromosomal disorders.
Mendelian disorders are caused due to alteration or mutation in a single gene. Examples- colour blindness, haemophilia, etc.

Complete answer:
Haemophilia- It is a sex-linked recessive disorder. Patient continues to bleed because of a defect in blood coagulation. The gene is located on the X chromosome. More males suffer from hemophilia than females because in male single gene for the defect is able to express as males have only one X chromosome. Females suffer from this disease only in homozygous conditions, i.e., $X^CX^C$.
Colour blindness- It is a sex-linked recessive disorder. It results in defects in either red or green cones of the eye, resulting in failure to discriminate between red and green colour. The gene is present on the X chromosome. It is more in males ($X^CY$) because of the presence of only one X chromosome as compared to two chromosomes of females.

So, the correct answer is option (D) all of these,

As in this cross the outcomes will be $25\%$ female progenies carry the genes for both haemophilic and colour blindness, $25\%$ male progenies carry only the gene for haemophilic, $25\%$ female progenies carry only the gene for colour blindness, $25\%$ male progenies carry the normal gene.

Note-
Mendelian disorders follow Mendel's principles of inheritance. There are various types of mendelian disorders- autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive and mitochondrial.
Humans have 23 pairs of chromosomes, 21 are autosomes and 1 pair of sex chromosomes.