Question

for the pedigree below indicate the mode of inheritance (for example: x - linked dominant, autosomal recessive, mitochondrial, etc.)

options:

• autosomal recessive
• x linked recessive
• mitochondrial
• autosomal dominant

Explanation:

1. Check for Autosomal Recessive Traits:

• In autosomal recessive inheritance, affected individuals (with the trait) often have unaffected parents (who are carriers).
• Here, Individual 10 (III - 10) is affected (black circle), and her parents (II - 3 and II - 4) are unaffected (white squares and circles), which fits the carrier - affected offspring pattern.
• Also, Individual 7 (II - 7) is affected (black square), and his parents (I - 1 and I - 2) are unaffected, further supporting recessive inheritance.
• For autosomal inheritance, the trait should not show sex - linked bias. The affected individuals include both males (II - 7) and females (III - 10), so it is not X - linked (X - linked recessive would show more affected males, and here a female is affected with unaffected parents).
• Mitochondrial inheritance is passed from mother to all offspring, but here affected individuals have unaffected mothers (e.g., II - 4 is unaffected but has an affected daughter III - 10; I - 1 is unaffected but has an affected son II - 7), so mitochondrial is out.
• Autosomal dominant would require at least one affected parent for an affected child, but III - 10 has unaffected parents, so dominant is out.

1. Eliminate Other Options:

• X - linked recessive: If it were X - linked recessive, affected females (like III - 10) would need to inherit the recessive allele from both parents. But her father (II - 3) is male, and if he were a carrier (for X - linked), he would be affected (since males have one X). But II - 3 is unaffected, so X - linked recessive is not possible.
• Mitochondrial: Mitochondrial DNA is inherited from the mother. If it were mitochondrial, all children of an affected mother would be affected, and an affected child must have an affected mother. But II - 7 (affected male) has an unaffected mother (I - 1), and III - 10 (affected female) has an unaffected mother (II - 4), so mitochondrial is incorrect.
• Autosomal dominant: In autosomal dominant, an affected individual must have at least one affected parent. III - 10 has two unaffected parents (II - 3 and II - 4), so autosomal dominant is incorrect.

Answer:

Autosomal recessive