A normal man marries a woman with colour blindness. Their children would be:

AIIMS Jodhpur SNO-2023

Pathology & Genetics

Hard

Appeared in: AIIMS Jodhpur SNO-2023

Explanation

Colour blindness is an X-linked recessive disorder, meaning the gene responsible is on the X chromosome and a person needs two copies (for females) or one copy (for males) of the recessive allele to express the trait.
The mother is colour blind, so her genotype is XᶜXᶜ. She will pass one of her affected X chromosomes (Xᶜ) to all of her children.
The father has normal vision, so his genotype is XᶜY. He passes his Y chromosome to his sons and his normal X chromosome (Xᶜ) to his daughters.
All sons will receive the Xᶜ from their mother and Y from their father, making their genotype XᶜY. Since they have only one X chromosome, they will be colour blind.
All daughters will receive the Xᶜ from their mother and the Xᶜ from their father, making their genotype XᶜXᶜ. They will have normal vision because the normal allele is dominant, but they will be carriers of the recessive allele.

Option B: This is incorrect because all sons will inherit an X chromosome with the recessive allele from their colour-blind mother, making them colour blind. Daughters will be carriers, not just 'normal' in the genetic sense, as they carry the recessive allele.
Option C: This is incorrect because all sons will inherit the affected X chromosome from their mother, making them colour blind, not normal.
Option D: This is incorrect for two reasons. First, daughters receive a normal X chromosome from their father, so they will be carriers with normal vision, not colour blind. Second, sons cannot be 'carriers' for X-linked traits; they are either affected (if they have the recessive allele) or unaffected (if they have the dominant allele).

Visual 1: Punnett Square - A diagram illustrating the genetic cross between a normal male (XᶜY) and a colour-blind female (XᶜXᶜ), showing the potential genotypes and phenotypes of their offspring.
Visual 2: Infographic - An infographic explaining the principles of X-linked recessive inheritance, showing how traits are passed from parents to children and why males are more commonly affected than females.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The concept tested is the inheritance pattern of X-linked recessive genetic disorders, specifically colour blindness as background academic context rather than a clinical decision trigger.
Understanding genetic inheritance patterns is crucial for patient education and genetic counseling. Nurses can help couples understand the risk of passing on genetic conditions to their children.
For families with a history of X-linked disorders like colour blindness, hemophilia, or Duchenne muscular dystrophy, genetic counseling can provide valuable information for family planning.
What if the roles were reversed (colour-blind father and normal, non-carrier mother)? In that case, all sons would be normal (receiving the mother's normal X and father's Y), and all daughters would be carriers (receiving the father's affected X and mother's normal X).

How to Approach the Question

First, identify the mode of inheritance mentioned in the question. Colour blindness is a classic example of an X-linked recessive trait.
Next, determine the genotypes of both parents based on their phenotypes (physical traits). A 'normal man' is XᶜY. A 'woman with colour blindness' must be homozygous for the recessive allele, so she is XᶜXᶜ.
Construct a Punnett square to visualize the possible combinations of alleles the offspring can inherit.
Analyze the Punnett square to determine the genotypes and corresponding phenotypes for all possible sons and daughters.
Compare your findings with the given options. The correct option will be the one that accurately describes all possible outcomes for the children (e.g., 100% of sons are colour blind, 100% of daughters are carriers).

Concept Tested & Keywords

Concept Tested: The concept tested is the inheritance pattern of X-linked recessive genetic disorders, specifically colour blindness.
Stem keywords: normal man, woman with colour blindness, children, inheritance
Lead-in keywords: would be

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