Which is the most likely inheritance pattern of the disease in the family pedigree cha given below?
**Question:** Which is the most likely inheritance pattern of the disease in the family pedigree chart given below?
**Correct Answer:** C. Autosomal Recessive Inheritance
**Core Concept:** Inheritance patterns in pedigrees are used to determine the mode of inheritance for a genetic disorder. There are four main types of inheritance patterns:
1. Autosomal Dominant: In this pattern, an affected individual has a 50% chance of passing the trait to each of their offspring. The affected parent in the pedigree (III-2) is heterozygous (carrier), but his children (III-3 and III-4) are homozygous (affected) because they inherited the abnormal allele from both parents.
2. Autosomal Recessive: In this pattern, an affected individual must inherit two copies of the abnormal gene (one from each parent). The parent (II-1) is a heterozygous carrier, meaning they have one normal gene and one abnormal gene. The children (III-3 and III-4) inherit the abnormal gene from their affected parent (III-2), making them homozygous (affected).
3. X-linked Dominant: In this pattern, affected males (III-3) inherit the abnormal gene from an affected parent (II-2). However, the affected females (III-2, III-4) are carriers and do not show symptoms.
4. X-linked Recessive: In this pattern, homozygous females (III-2, III-4) are affected, while heterozygous carriers (II-2, III-3) are unaffected. An affected male (III-3) must inherit the abnormal gene from his affected parent (II-2).
5. Sex-linked Mosaicism: In this pattern, individuals are affected but have a mosaic pattern of abnormal cells, which may lead to mild or no symptoms. This option is not relevant to the provided pedigree.
**Why the Correct Answer is C:**
The correct answer is C: Autosomal Recessive Inheritance because:
1. The affected individuals (III-3 and III-4) inherit the abnormal gene from their affected parent (III-2), who is heterozygous (carrier).
2. The unaffected parents (II-1 and II-2), as well as the unaffected child (III-1), do not have the abnormal gene, indicating that the inheritance pattern is not X-linked Dominant or Recessive, or Sex-linked Mosaicism.
3. The affected females (III-2 and III-4) are carriers, while the affected males (III-3) inherit the abnormal gene from their affected parent (III-2).
**Why the Wrong Answers are Incorrect:**
A. Autosomal Dominant (Option A): In this pattern, affected individuals inherit the abnormal gene from one affected parent (II-1 or II-2) and show symptoms regardless of gender. In this pedigree, only the females (III-2, III-4) are