Most common group of diseases following mendelian inheritance are –
## **Core Concept**
Mendelian inheritance refers to the pattern of inheritance seen for traits determined by a single gene with two alleles, one inherited from each parent. These diseases follow the classic laws of inheritance proposed by Gregor Mendel.
## **Why the Correct Answer is Right**
The correct answer, **Autosomal Dominant**, represents the most common group of diseases following Mendelian inheritance. This is because autosomal dominant diseases only require one copy of the mutated gene to express the condition. A single allele is enough to cause the disorder. Examples include Huntington's disease and Marfan syndrome. The prevalence of such diseases in the population is relatively higher because they can be inherited from either parent and do not require both parents to be affected.
## **Why Each Wrong Option is Incorrect**
- **Option A: X-linked Recessive** - These diseases are less common than autosomal dominant diseases because they are linked to the X chromosome. Males are more frequently affected than females since they have only one X chromosome. Females would need to inherit two copies of the mutated gene (one from each parent) to express the condition. Examples include hemophilia A and Duchenne muscular dystrophy.
- **Option B: Autosomal Recessive** - While these diseases are also Mendelian, they are less common than autosomal dominant diseases. They require an individual to inherit two copies of the mutated gene (one from each parent) to express the condition. Carriers, who have one mutated gene, typically do not show symptoms but can pass the gene to their offspring. Examples include cystic fibrosis and sickle cell disease.
- **Option D: Mitochondrial** - Mitochondrial diseases are caused by mutations in the mitochondrial DNA. They are less common and have a unique pattern of inheritance since only egg cells contribute mitochondria to the fertilized egg. These diseases can affect both males and females, but only females can pass them on. Examples include Leber's hereditary optic neuropathy.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **autosomal dominant diseases** often have a family history that can be traced, and they can present with variable expressivity and penetrance. This means that individuals with the same genotype may exhibit different levels of severity of the disease.
## **Correct Answer:** . **Autosomal Dominant**