In fruit flies, the gene for red eyes(R) is dominant over the gene for white eyes(r) and is sex linked. If a true breeding red eyed male, all the offspring are red eyed. However, if a true breeding white eye breeding white eye female is mated with a red eyed male, all the offspring will be white eyed. Explain this apparent contradiction using genetic cross

The apparent contradiction can be explained by understanding the concept of sex-linked genes and dominance in genetics.

In fruit flies, the gene for eye color is located on the X chromosome, which is a sex chromosome. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

Step 1: Understanding the True Breeding Red Eyed Male A true breeding red eyed male would have the genotype XR Y (R for the dominant red eye gene). When this male is mated with any female, all his offspring will receive his X chromosome with the dominant red eye gene, resulting in all red-eyed offspring. This is because the red eye gene (R) is dominant over the white eye gene (r).

Step 2: Understanding the True Breeding White Eyed Female A true breeding white eyed female would have the genotype Xr Xr (r for the recessive white eye gene). When this female is mated with a red eyed male (XR Y), the male can only pass on either his X or Y chromosome.

Step 3: The Genetic Cross If the male passes on his X chromosome (XR), the offspring will be female (XR Xr) and will have red eyes because the red eye gene is dominant. However, if the male passes on his Y chromosome, the offspring will be male (Xr Y) and will have white eyes because there is no dominant red eye gene on the Y chromosome to mask the recessive white eye gene on the X chromosome from the mother.

So, in this case, all the male offspring will have white eyes, and all the female offspring will have red eyes. This explains the apparent contradiction.

The apparent contradiction can be explained by understanding the concept of sex-linked genes and dominance in genetics.

Step 1: Understand the Basics In fruit flies, the gene for eye color is located on the X chromosome, making it a sex-linked trait. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

Step 2: Understand the Dominance The gene for red eyes (R) is dominant over the gene for white eyes (r). This means that an individual only needs one copy of the red eye gene to have red eyes.

Step 3: Understand the First Scenario In the first scenario, a true breeding red-eyed male

The apparent contradiction can be explained by understanding the concept of sex-linked genes and dominance in genetics.

In fruit flies, the gene for eye color is located on the X chromosome, which is a sex chromosome. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

Step 1: Understanding the Genotypes A true breeding red-eyed male would have the genotype XR Y (where R represents the dominant red-eye gene). This is because males only have one X chromosome, and for them to have red eyes, this single X chromosome must carry the dominant red-eye gene.

A true breeding white-eyed female would have the genotype Xr Xr (where r represents the recessive white-eye gene). This is because females have two X chromosomes, and for them to express the recessive trait (white eyes), both X chromosomes must carry the recessive gene.

Step 2: The First Cross When a true breeding red-eyed male (XR Y) mates with a female (any genotype), all the offspring will have red eyes. This is because the male passes on the dominant red-eye gene (R) to all his offspring. The offspring receive one X chromosome from their mother and one X or Y chromosome from their father. If they receive the X chromosome from their father, it will carry the dominant red-eye gene, resulting in red eyes.

Step 3: The Second Cross When a true breeding white-eyed female (Xr Xr) mates with a red-eyed male (XR Y), all the offspring will have white eyes. This is because the female passes on the recessive white-eye gene (r) to all her offspring. The male offspring will be Xr Y (white-eyed) because they receive the X chromosome carrying the white-eye gene from their mother and the Y chromosome from their father. The female offspring will be Xr XR (red-eyed) because they receive one X chromosome carrying the white-eye gene from their mother and one X chromosome carrying the red-eye gene from their father. However, since the gene is sex-linked and the Y chromosome in males does not carry the allele for eye color, the white-eye gene (r) on the X chromosome is expressed, resulting in white eyes.

So, the apparent contradiction is due to the fact that the gene for eye color in fruit flies is sex-linked and located on the X chromosome.