49. The probability of a son to be color blind for parent with colorblind father and normal homozygous mother would be
(1) 0%         (2) 25%
(3) 50%       (4) 100%

The probability that a son will be color blind if the father is color blind and the mother is homozygous normal (non-carrier) is 0%.

Explanation of the genetics and options

Color blindness, especially red-green color blindness, is usually inherited as an X-linked recessive trait. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). Since males have only one X chromosome, inheriting a defective gene for color blindness on the X chromosome results in the phenotype expressing color blindness. Females, having two X chromosomes, must inherit the defective gene on both X chromosomes to express color blindness; otherwise, if only one X is defective, they are carriers without symptoms.

• Father with color blindness genotype: XᶜY (X chromosome carrying color blind allele)

• Mother with homozygous normal genotype: XX (both normal alleles, no colorblind gene)

In this case:

• Sons get the Y chromosome from the father and one X chromosome from the mother.

• Since the mother is homozygous normal (XX), all sons will inherit a normal X chromosome.

• Therefore, none of the sons will be color blind (0% probability).

Explanation of each answer choice

(1) 0%: Correct, because a son inherits the Y chromosome from the color blind father and a normal X chromosome from the mother, so he will not be color blind.

(2) 25%: Incorrect, color blindness inheritance probability in sons isn’t 25% in this scenario because the mother has no defective allele to pass.

(3) 50%: Incorrect, this applies when the mother is a carrier (XᵇXᶜ) and father is normal (XY), where sons have a 50% chance by inheriting the defective X.

(4) 100%: Incorrect, this would mean all sons are color blind, possible only if mother is homozygous color blind (XᶜXᶜ), which is very rare.

Introduction

Color blindness is a common X-linked recessive genetic condition. If a father is color blind and the mother is normal homozygous, the chance of their son being color blind is zero. This article explains the inheritance pattern and clarifies common misconceptions.

Detailed Explanation

Color blindness genes are carried on the X chromosome. A male inherits his single X chromosome from his mother and the Y chromosome from his father. Since the mother is homozygous normal, she provides a normal X chromosome to her son, who therefore cannot inherit color blindness from his father’s X chromosome (because sons do not inherit the father’s X). Hence, sons will not be color blind in this genetic scenario.

Understanding the Options

• 0% is the correct probability because sons always inherit the Y chromosome from their father.

• 25% and 50% probabilities occur only when the mother is a carrier or heterozygous for the color blindness gene.

• 100% occurs only if the mother is homozygous color blind, which is very rare.

Knowing this pattern helps understand X-linked trait inheritance better and predict genetic outcomes accurately.

This explanation affirms that the correct answer to the question is (1) 0% with detailed reasoning and clarifies why other options do not apply in this specific genetic situation.