Question

A male, named John, with Xg blood type negative mates with a female (Sarah) who is Xgpositive. It is notable that Sarah's father was Xg negative. What are the probable genotypes andphenotypes of the children of John and Sarah?​

Answer 1

John's children will inherit an X-linked Xg allele from both parents, resulting in a 50% chance of Xg positive or negative offspring if Sarah is heterozygous for the trait. If Sarah is homozygous, all offspring will be Xg positive.

Step-by-step explanation:

Genotypes and Phenotypes of John and Sarah's Children

The question concerns the inheritance of the Xg blood type, which is an X-linked characteristic. Given that John is Xg negative (XgXg) and Sarah is Xg positive (XgXg or XgXg^+ since she must have one Xg negative allele inherited from her father), we can deduce the possible genotypes and phenotypes of their offspring.

For each child, John can only pass an Xg or Y chromosome (resulting in a female or male child, respectively), while Sarah can pass either an Xg^+ or Xg allele if she is heterozygous or only her Xg^+ allele if homozygous:

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• If Sarah is heterozygous (XgXg^+), the children can have the following genotypes and phenotypes:
  
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  • XgXg (Xg negative female)
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  • XgXg^+ (Xg positive female)
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  • XgY (Xg negative male)
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  • Xg^+Y (Xg positive male)
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• If Sarah is homozygous (Xg^+Xg^+), the children can be:
  
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  • Xg^+Xg (Xg positive female)
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  • Xg^+Y (Xg positive male)
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Note that the Xg blood type is different from the ABO blood type, but similarly, it is inherited via an X-linked pattern. In this scenario, the probability that a child will be Xg positive or Xg negative depends on whether Sarah is heterozygous or homozygous for the Xg allele.