Predict the potential effect of the Lyon hypothesis on the retina of a human female heterozygous for the X-linked red-green color blindness trait.

Verified step by step guidance

1. Understand the Lyon hypothesis, which states that in female mammals, one of the two X chromosomes in each cell is randomly inactivated during early embryonic development, leading to a mosaic pattern of X-linked gene expression.
2. Recognize that the female in question is heterozygous for the X-linked red-green color blindness trait, meaning she has one X chromosome with the normal allele and one X chromosome with the allele for red-green color blindness.
3. Consider that due to random X-inactivation, some retinal cells will express the normal allele (from the active X chromosome with the normal gene), while others will express the allele for color blindness (from the active X chromosome carrying the mutation).
4. Predict that this mosaic expression in the retina could lead to a patchy or mixed population of cone cells, some functioning normally and others deficient in red-green color perception, potentially resulting in a variable or partial color vision phenotype.
5. Conclude that the overall effect on the female's color vision depends on the proportion and distribution of cells expressing each X chromosome, which can vary between individuals due to the randomness of X-inactivation.

Key Concepts

Lyon Hypothesis (X-Chromosome Inactivation)

The Lyon hypothesis explains that in female mammals, one of the two X chromosomes in each cell is randomly inactivated during early embryonic development. This process creates a mosaic pattern of gene expression, where some cells express genes from the maternal X and others from the paternal X, affecting traits linked to the X chromosome.

X-Linked Red-Green Color Blindness

Red-green color blindness is a common X-linked recessive trait caused by mutations in genes coding for photopigments in the retina. Males with the mutation on their single X chromosome express the trait, while females must be homozygous to be fully color blind; heterozygous females are typically carriers with normal vision but can show mosaic expression.

Mosaicism in Retinal Cells

Due to X-chromosome inactivation, heterozygous females for X-linked traits like red-green color blindness have retinal cells expressing either the normal or mutant allele. This mosaicism can lead to patches of retina with normal color vision and patches with deficient color perception, potentially affecting overall color discrimination.