Q.8 Haplodiploid system of sex determination is found in
(1) Humans
(2) Grasshoppers
(3) Birds
(4) Honey bees
Haplodiploid Sex Determination: MCQ Answer Revealed
Haplodiploidy is a sex determination system where males develop from unfertilized eggs (haploid) and females from fertilized eggs (diploid). This creates unique genetic relatedness patterns, explaining eusocial behavior in insects. In the MCQ: “Haplodiploid system of sex determination is found in,” the correct answer is (4) Honey bees.
Honey bees (Apis mellifera) exemplify haplodiploidy: queens/workers (diploid females) from fertilized eggs, drones (haploid males) from unfertilized eggs. This system drives their altruism—sisters share 75% genes (higher than with mothers!).
Correct Answer: Option (4) – Honey Bees
Mechanism:
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Fertilized egg (2n) → Diploid female (queen/worker)
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Unfertilized egg (n) → Haploid male (drone)
Key Evidence: Hamilton’s Rule of Kin Selection (rB>C) was inspired by hymenopteran haplodiploidy. Studies in Nature confirm this across bees, ants, wasps.
Evolutionary Advantage: Females 3x more related to sisters than own offspring, favoring worker sterility.
Why Not the Other Options? Detailed Explanations
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Option (1) Humans: Incorrect. Humans use XX/XY chromosomal sex determination. Females XX (fertilized), males XY (fertilized). No haplodiploidy—both sexes diploid.
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Option (2) Grasshoppers: Incorrect. Most orthopterans like grasshoppers use XO/XX system. Males XO (sex chromosome missing), females XX. Fertilization determines sex; both diploid.
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Option (3) Birds: Incorrect. Birds employ ZW/ZZ system (female heterogametic). Females ZW, males ZZ. Chromosomal, not haplodiploid—both sexes diploid from fertilized eggs.
Comparison Table: Sex Determination Systems
| Species | System | Males | Females | Fertilization? | Haplodiploid? |
|---|---|---|---|---|---|
| (1) Humans | XX/XY | XY | XX | Both fertilized | ❌ No |
| (2) Grasshoppers | XO/XX | XO | XX | Both fertilized | ❌ No |
| (3) Birds | ZW/ZZ | ZZ | ZW | Both fertilized | ❌ No |
| (4) Honey bees | Haplodiploid | Haploid (n) | Diploid (2n) | Males unfertilized | ✅ Yes |
Biological Significance & Exam Relevance
Haplodiploidy explains Hymenoptera eusociality (bees, ants, wasps)—90% of eusocial insects use it. Crucial for NEET, CSIR NET Genetics, where it contrasts chromosomal systems. Mnemonic: “Haplo-Drone” = Honey bee drones (haploid males).
Fun Fact: Queen bees control fertilization via spermatheca valve—choosing sister vs. son production!
