Pedigree analysis–Analyze the following pedigree and give the mode of inheritance:
## **Core Concept**
The question requires the analysis of a pedigree chart to determine the mode of inheritance of a particular trait or disease. Pedigree analysis is a tool used in genetics to study the inheritance of traits and diseases within families. It involves examining the family tree to identify patterns of inheritance.
## **Why the Correct Answer is Right**
The correct answer, , indicates an autosomal dominant pattern of inheritance. In autosomal dominant inheritance, a single copy of the dominant allele is enough to cause the condition. This means that if one parent is affected, each child has a 50% chance of inheriting the condition. The key features of autosomal dominant inheritance include: affected individuals have at least one affected parent (unless the condition results from a new mutation), males and females are equally likely to be affected, and the condition can be passed from one generation to the next.
## **Why Each Wrong Option is Incorrect**
* **Option A:** - This option suggests an autosomal recessive pattern of inheritance. Autosomal recessive conditions require an individual to have two copies of the recessive allele (one from each parent) to be affected. Carriers, who have one copy of the recessive allele, are usually not affected but can pass the allele to their offspring. This does not match the pattern described for the correct answer.
* **Option B:** - This option implies an X-linked recessive pattern. X-linked recessive conditions are caused by mutations in genes on the X chromosome. Males, having only one X chromosome, are more frequently affected than females, who would need two copies of the mutated gene (one on each X chromosome) to express the condition. This does not fit the description of the correct answer.
* **Option D:** - This option indicates an X-linked dominant pattern of inheritance. In X-linked dominant conditions, females are more frequently affected than males because they have two X chromosomes, and males are more severely affected since they have only one X chromosome. The pattern does not match the autosomal dominant description provided.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl to remember is that in **autosomal dominant** conditions, **each child of an affected parent has a 50% chance of inheriting the mutated gene**, making it crucial for genetic counseling in families with a history of such conditions.
## **Correct Answer:** . Autosomal dominant