Question

Example of Non-Mendelian disorder:

• A. Cystic fibrosis
• B. Haemophilia
• C. Down’s syndrome
• D. Thalassemia

Answer 1

The Correct Option is C

First, let's define Mendelian and Non-Mendelian disorders:

• Mendelian Disorders: These are genetic disorders caused by mutations in a single gene and follow the laws of Mendelian inheritance (dominant, recessive, X-linked). Examples include Cystic Fibrosis, Haemophilia, and Thalassemia.
• Non-Mendelian Disorders: These disorders do not follow simple Mendelian patterns of inheritance. They often involve multiple genes, environmental factors, or chromosomal abnormalities.

Now let's analyze the options:

• Cystic Fibrosis: This is an autosomal recessive disorder caused by a mutation in the CFTR gene. It follows Mendelian inheritance.
• Haemophilia: This is typically an X-linked recessive disorder caused by mutations in genes responsible for blood clotting. It follows Mendelian inheritance.
• Down's syndrome: This is a chromosomal disorder caused by the presence of an extra copy of chromosome 21 (Trisomy 21). It does NOT follow Mendelian inheritance patterns. The extra chromosome arises due to errors in chromosome segregation during meiosis (nondisjunction).
• Thalassemia: This is a group of autosomal recessive blood disorders caused by mutations in genes responsible for producing hemoglobin. It follows Mendelian inheritance.

Therefore, the example of a Non-Mendelian disorder among the options is Down's syndrome.

Answer 2

Down's syndrome is caused by the presence of an extra copy of chromosome 21, known as trisomy 21. It is not inherited in a Mendelian pattern, which typically involves the transmission of a single gene from parents to offspring. Instead, Down's syndrome occurs due to a random error during the formation of reproductive cells or early embryonic development.