Question

Honey bees are haplodiploid, which means that the relatedness is, on average, expected to be 0.75 between

• A. brother-brother pairs with the same parents.
• B. brother-sister pairs with the same parents.
• C. mated female-male pair.
• D. sister-sister pairs with the same parents.

Hint:

Key concept for GATE Ecology: In haplodiploidy, {sisters are more closely related to each other than to their own offspring}, which helps explain the evolution of eusocial behavior in insects like bees and ants.

Answer 1

The Correct Option is D

Step 1: Understand haplodiploidy.
In haplodiploid organisms such as honey bees:
-- Females (workers and queens) are diploid, developing from fertilized eggs.
-- Males (drones) are haploid, developing from unfertilized eggs.
Thus, males carry only one set of chromosomes, all inherited from their mother.
Step 2: Calculate sister–sister relatedness.
Two sisters inherit:
-- Half of their genes from the mother (with a probability of $0.5$ of sharing maternal alleles).
-- All of their genes from the father, because the father is haploid and passes the same genome to all daughters.
Therefore, relatedness between sisters is: \[ r = \frac{1}{2} \times 0.5 + \frac{1}{2} \times 1 = 0.25 + 0.5 = 0.75 \] Step 3: Analyze other options.
(A) Brother–brother pairs:
Brothers are haploid and develop from unfertilized eggs; they do not share a father.
Relatedness is lower than 0.75.
(B) Brother–sister pairs:
A sister shares only maternal genes with her brother.
Relatedness is $0.25$, not $0.75$.
(C) Mated female–male pair:
Mates are not genetically related.
Relatedness is approximately zero.
Step 4: Conclusion.
In haplodiploid systems like honey bees, the unusually high relatedness of $0.75$ occurs between: \[ \boxed{\text{sister–sister pairs with the same parents}} \]