Red-green colour blindness is an X-linked recessive trait with the alleles $X^R$: normal color vision $X^e$: red-green colour blind Examine the following pedigree. With respect to this gene, it is reasonable to predict that individual A. II3 must be $X^R X^R$. B. II4 must be $X^R X^e$. C. II4 has a two in three chance of being $X^R X^R$. D. IV1 has a one in four chance of being colour blind.

SSCE VCE Biology Mechanisms of Inheritance: Red-green colour blindness is an

Red-green colour blindness is an X-linked recessive trait with the alleles $X^R$: normal color vision $X^e$: red-green colour blind Examine the following pedigree - VCE - SSCE Biology - Question 16 - 2011 - Paper 1

Question 16

Red-green colour blindness is an X-linked recessive trait with the alleles $X^R$: normal color vision $X^e$: red-green colour blind Examine the following pedigree. ... show full transcript

Worked Solution & Example Answer:Red-green colour blindness is an X-linked recessive trait with the alleles $X^R$: normal color vision $X^e$: red-green colour blind Examine the following pedigree - VCE - SSCE Biology - Question 16 - 2011 - Paper 1

Step 1

II3 must be $X^R X^R$.

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Answer

To determine if II3 can be $X^R X^R$ , we analyze the pedigree. Since II2 is normal (filled square), and both parents can contribute an X chromosome, if II2 is $X^R X^e$ , II3 cannot be $X^R X^R$ since there’s a chance II3 could inherit $X^e$ . Thus, this statement is false.

Step 2

II4 must be $X^R X^e$.

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Answer

To evaluate II4, we notice II3 (male) cannot carry $X^R$ while being normal, implying that II4 presents a genotype that includes $X^e$ for the colorblind trait. Thus, II4 most likely must be $X^R X^e$ , making this statement true.

Step 3

II4 has a two in three chance of being $X^R X^R$.

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Answer

For II4 to have a two in three chance of being $X^R X^R$ , considering two males contributing an X chromosome to II4, we must conclude that individual probabilities must align directly with direct pattern inheritance, giving a greater likelihood of being $X^R X^e$ instead. Hence, this statement is false.

Step 4

IV1 has a one in four chance of being colour blind.

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Answer

Since IV1 inherits X chromosomes from both parents, one being $X^e$ , the likelihood of inheriting the colour blind trait is 1 in 4, as it can be $X^R X^R$ , $X^R X^e$ , or $X^e X^e$ . Therefore, this statement is true.

Red-green colour blindness is an X-linked recessive trait with the alleles $X^R$: normal color vision $X^e$: red-green colour blind Examine the following pedigree - VCE - SSCE Biology - Question 16 - 2011 - Paper 1

Worked Solution & Example Answer:Red-green colour blindness is an X-linked recessive trait with the alleles $X^R$: normal color vision $X^e$: red-green colour blind Examine the following pedigree - VCE - SSCE Biology - Question 16 - 2011 - Paper 1

II3 must be $X^R X^R$.

II4 must be $X^R X^e$.

II4 has a two in three chance of being $X^R X^R$.

IV1 has a one in four chance of being colour blind.

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