The figure below illustrates a family that has several members who are affected

Question

The figure below illustrates a family that has several members who are affected with a disorder that is due to a mutation in an autosomal gene. The disease-causing mutation is in the Marker 4 region of the boxed chromosome, and is linked to the 4 allele of Marker 4. Paternally derived alleles are listed to the left for each person's genotype. What can you tell me about the pattern of activity of this gene? Explain your answer, giving me all the individuals in the pedigree who provide evidence to support your conclusion.

Explanation / Answer

The given pedigree of a family represents the occurrence of a disorder due to mutation in an autosomal gene, represented by the marker 4 of the boxed chromosome, and the mutated allele represented by the number 4.

Individuals I and II form the first line of parent generation, in which the male parent (I-1) is affected by the disorder, and has a single mutated allele 4, the other allele is normal. Their children in the second generation, one daughter (II-2) and a son (II-3) are both affected by the disorder. II-3 marries an unaffected (normal) male (II-1), their children (III-1 & III-2) are unaffected by the disorder, even though they carry the mutated allele (allele 4 in the boxed chromosome) obtained from their mother (II-2). On the other hand, when II-3 marries an unaffected (normal) female, they produce 2 children (III-3 & III-4), both affected with the disorder.

So, when the mutated allele is obtained from the paternal chromosome, it activates the allele, producing the disorder (as evident in third generation individuals, III-3 & III-4, as well as second generation, II-2 & II-3). However, when the mutated allele is obtained from the maternal chromosome, the allele remains silent, and does not produce the disorder (as in the case of individuals of third generation, III-1 & III-2).

Thus, although the mutated allele for the gene can be inherited from either parent, its activity depends on the origin of the allele. Only when the allele is inherited from a paternal chromosome, it is active, and produces the disorder in the individual carrying it.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.