A woman with normal vision, but whose father was colour-blind, marries a colour-blind man. Suppose that the fourth child of this couple was a boy. This boy-
A woman with normal vision, but whose father was colour-blind, marries a colour-blind man. Suppose that the fourth child of this couple was a boy. This boy-
The correct option is B maybe colour blind or may be of normal vision
The correct option is B.
Explanation of correct option:
- Colour blindness is a type of disorder in which the person faces trouble in seeing or identifying specific colors like red, green, and blue. They also have difficulties identifying the differences between color shades.
- It is a recessive disorder since it occurs when an individual has defects in all the X chromosomes of the cell.
- Males inherit one ‘X’ chromosome from their mother; hence they can develop the disease if they inherit the affected chromosome. Females are heterozygous since they can only develop the disease when they have defects in both ‘X’ chromosomes.
- If a normal-visioned woman had a color-blind father, the woman will be a carrier (XXc). When a carrier woman marries a color-blind man (XY), their offspring will include a carrier daughter, color-blind daughter, normal son, and color-blind son (Table 1). Hence, the fourth son may be color blind or have normal vision.
Table 1: Carrier woman (XXc) X Colour-blind man (XYXXS)
Gametes Xc
Y
X
XXc
(Carrier daughter)
XY
(Normal son)
Xc
XcXc
(Colour-blind daughter)
XcY
(Colour-blind son)
Explanation of incorrect option:
Option A:
When a carrier woman marries a color-blind man, their fourth son can be color blind or have normal vision.
Option C:
Male receives one X chromosome from the mother, hence they will be color blind even if they have one affected allele. They are never heterozygous for the color-blind mutant allele.
Option D:
The fourth son of a carrier mother and color-blind father may be color-blind or have normal vision.
Final answer: A normal-visioned woman whose father was color-blind marries a color-blind man. Their fourth son may be color blind or may be of normal vision.
maybe colour blind or may be of normal vision
The correct option is B.
Explanation of correct option:
- Colour blindness is a type of disorder in which the person faces trouble in seeing or identifying specific colors like red, green, and blue. They also have difficulties identifying the differences between color shades.
- It is a recessive disorder since it occurs when an individual has defects in all the X chromosomes of the cell.
- Males inherit one ‘X’ chromosome from their mother; hence they can develop the disease if they inherit the affected chromosome. Females are heterozygous since they can only develop the disease when they have defects in both ‘X’ chromosomes.
- If a normal-visioned woman had a color-blind father, the woman will be a carrier (XXc). When a carrier woman marries a color-blind man (XY), their offspring will include a carrier daughter, color-blind daughter, normal son, and color-blind son (Table 1). Hence, the fourth son may be color blind or have normal vision.
Table 1: Carrier woman (XXc) X Colour-blind man (XYXXS)
| Gametes | Xc | Y |
X | XXc (Carrier daughter) | XY (Normal son) |
Xc | XcXc (Colour-blind daughter) | XcY (Colour-blind son) |
Explanation of incorrect option:
Option A:
When a carrier woman marries a color-blind man, their fourth son can be color blind or have normal vision.
Option C:
Male receives one X chromosome from the mother, hence they will be color blind even if they have one affected allele. They are never heterozygous for the color-blind mutant allele.
Option D:
The fourth son of a carrier mother and color-blind father may be color-blind or have normal vision.
Final answer: A normal-visioned woman whose father was color-blind marries a color-blind man. Their fourth son may be color blind or may be of normal vision.
