Title: Understanding the Inheritance of Colour Blindness: Genotypes of Parents and Offspring

Meta Description: Learn about the inheritance of color blindness in humans, a sex-linked recessive trait, and determine the genotypes of the parents based on a color-blind son’s condition.

Slug: inheritance-of-colour-blindness-genotypes-of-parents

Key Phrase: colour blindness inheritance, sex-linked recessive trait, genotypes of parents, color-blind son

Introduction: Understanding Colour Blindness Inheritance

Colour blindness is a common visual impairment that affects the ability to perceive certain colors correctly. It is most often a sex-linked recessive trait, meaning the gene responsible for this condition is located on the X chromosome. Understanding how this trait is inherited can help determine the possible genotypes of parents if they have a child with colour blindness.

Colour Blindness: A Sex-Linked Recessive Trait

In humans, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). The gene responsible for color blindness is located on the X chromosome. Since color blindness is a recessive trait, the following genetic principles apply:

• A male only needs one recessive allele on his X chromosome to be color-blind (XbY).

• A female needs two recessive alleles (XbXb) to be color-blind. If she has only one recessive allele, she will be a carrier (XBXb), meaning she will not express the condition but can pass it on to her offspring.

Genotype Determination Based on the Son’s Condition

In the scenario described, a couple with normal colour vision has a colour-blind son. Let’s break down the genotypes of the parents based on this information:

1. Father’s Genotype: The father has normal color vision, so his genotype is XBY (he has one normal X chromosome and one Y chromosome). Since males inherit their X chromosome from their mother and their Y chromosome from their father, the father cannot pass on a color-blind allele to his son.

2. Mother’s Genotype: The mother has normal color vision but must be a carrier of the color blindness allele. This is because she has passed on the color-blind allele to her son. Therefore, her genotype must be XBXb, meaning she carries one normal allele and one color-blind allele.

How the Son Inherited His Genotype

Since the son is color-blind, he inherited the Xb allele from his mother and the Y chromosome from his father. His genotype is XbY, where the X chromosome carries the color-blind allele, and the Y chromosome comes from his father.

The Correct Genotypes of the Parents

Based on the inheritance pattern and the son’s condition, the correct genotypes of the parents are:

(2) XBXb and XBY

This means the mother is a carrier of the color blindness allele, and the father has normal color vision but passed on the Y chromosome to his son.

Conclusion: Understanding Inheritance Patterns

Colour blindness is a sex-linked recessive condition that follows a predictable pattern of inheritance. In this case, the mother must be a carrier of the color-blind allele, and the father must have normal color vision. By understanding these principles, it becomes easier to determine the genotypes of parents and predict the likelihood of having a color-blind child.