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Question
sex linked trait questions
colorblindness is a sex linked disease carried on the x chromosome. this disease typically only affects males. cross a colorblind woman with a normal man. what are the chances that the male children will be colorblind? (hint* only look at the males to determine the percentage)
- cross a woman who is a carrier of colorblindness with a colorblind man. what percentage of their children will be colorblind?
- who is most affected by colorblindness, girls or boys? why? (most important question).
Brief Explanations
- Let \(X^c\) represent the color - blind allele and \(X^C\) represent the normal allele. The woman (carrier) has the genotype \(X^CX^c\) and the man (color - blind) has the genotype \(X^cY\).
- Using a Punnett square:
- The possible gametes from the woman are \(X^C\) and \(X^c\), and from the man are \(X^c\) and \(Y\).
- The offspring genotypes are \(X^CX^c\) (female, carrier), \(X^cX^c\) (female, color - blind), \(X^CY\) (male, normal), \(X^cY\) (male, color - blind).
- Out of 4 possible offspring, 2 (\(X^cX^c\) and \(X^cY\)) are color - blind. So the percentage is \(\frac{2}{4}\times100\% = 50\%\).
- Males have only one \(X\) chromosome. If that \(X\) chromosome has the color - blind allele (\(X^c\)), they will be color - blind (\(X^cY\)). Females have two \(X\) chromosomes. They need to have the color - blind allele on both \(X\) chromosomes (\(X^cX^c\)) to be color - blind. Since it is less likely for a female to inherit two color - blind alleles compared to a male inheriting one, boys are more affected.
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- \(50\%\)
- Boys are most affected. Males have one \(X\) chromosome. If it has the color - blind allele (\(X^c\)), they are color - blind (\(X^cY\)). Females need two \(X^c\) alleles (\(X^cX^c\)) to be color - blind.