Question

Arrange the following inbreeding types in order of its co-efficient from largest to smallest :
• [A.] Uncle-niece marriage
• [B.] Second cousin marriage
• [C.] First cousin marriage
• [D.] Third cousin marriage
Choose the correct answer from the options given below :

• A. A-C-B-D
• B. A-B-C-D
• C. A-D-B-C
• D. A-C-D-B

Hint:

Closer biological relationships always produce higher inbreeding coefficients. Uncle-niece marriage has a higher coefficient than cousin marriages.

Answer 1

The Correct Option is A

Concept: The coefficient of inbreeding refers to the probability that two alleles in an individual are identical by descent due to common ancestry. In biological anthropology and human genetics, closer biological relationships produce a higher inbreeding coefficient. Thus:
• Closer relatives produce higher inbreeding,
• Distant relatives produce lower inbreeding,
• Degree of genetic similarity determines the coefficient value. The order depends upon the closeness of the biological relationship.

Step 1: Understanding inbreeding coefficient. The inbreeding coefficient measures: \[ \text{Probability of inheriting identical genes from common ancestors} \] If marriage occurs between close relatives:
• Shared ancestry increases,
• Genetic similarity becomes higher,
• Inbreeding coefficient rises. Therefore, closer kinship implies a larger coefficient.

Step 2: Analyzing Uncle-niece marriage. Uncle-niece marriage involves a very close biological relationship. The coefficient of inbreeding here is relatively high because:
• One partner belongs to the parental generation,
• Large amount of genetic material is shared,
• Common ancestry is extremely close. Hence: \[ \text{Uncle-niece marriage has the highest coefficient among the given options.} \] So: \[ A = \text{Highest} \]

Step 3: Analyzing First cousin marriage. First cousins share grandparents as common ancestors. Their genetic relationship is closer than:
• Second cousins,
• Third cousins. Therefore: \[ \text{First cousin marriage has the next highest coefficient after uncle-niece marriage.} \] Thus: \[ C = \text{Second highest} \]

Step 4: Analyzing Second cousin marriage. Second cousins share great-grandparents. This relationship is more distant than first cousins. Hence:
• Genetic similarity decreases,
• Inbreeding coefficient becomes smaller. Therefore: \[ B = \text{Third in order} \]

Step 5: Analyzing Third cousin marriage. Third cousins share even more distant ancestors. Thus:
• Shared genes become minimal,
• Inbreeding coefficient becomes the smallest among the options. Therefore: \[ D = \text{Smallest} \]

Step 6: Arranging from largest to smallest. The correct order becomes: \[ A > C > B > D \] Thus: \[ \boxed{\text{A-C-B-D}} \] Hence, the correct answer is: \[ \boxed{\text{(A) A-C-B-D}} \]