Question

Mode of inheritance of haemophilia resembles that of

• A. Myopia
• B. Skin colour
• C. Colour blindness
• D. Night blindness

Answer 1

The correct option is C Colour blindness

Both haemophilia and colour blindness skips generations; the unaffected parents have diseased progeny which means that the traits are present in recessive condition in parents. Males are more affected than females which means that traits are dependent on sex of individual; both are sex linked traits. Colour blindness and haemophilia are X-linked recessive disorders. One copy of the affected gene in males in each cell is sufficient to cause the disorder (X${}^c$Y or X${}^h$Y ). Females with two copies of the affected gene show the disorder (X${}^c$X${}^c$ or X${}^h$X${}^h$). The heterozygous females serve as the carrier for the disease. Thus, option C is correct. Night blindness is impaired ability to see in dim light; it is an autosomal recessive disorder and is inherited independently of the sex of individual which makes option D incorrect. When the trait is controlled by one or more genes, the dominant alleles of which show a cumulative effect, i.e., only part of the trait is expressed by single dominant allele and expression of a full trait requires the presence of all dominant allele, it is quantitative inheritance. The phenotype of offspring depends on a number of dominant alleles; human skin colour follows quantitative inheritance which makes option B incorrect. Nearsightedness, or myopia is an inability to see the far located objects clearly and is inherited in autosomal dominant manner. The correct option is C.