# DBT JRF 2022 — Question 85

Exam: DBT JRF 2022 · Section: B · Topic: Genetics › Polyploidy & Interspecies Hybridization · Difficulty: Medium

## Question

A haploid sperm from one species and a haploid egg from another species may form a diploid interspecies hybrid. Meiosis in these plants generally fails but can also lead to rare duplicated gametes called:

## Options

- **A.** Allopolyploid
- **B.** Aneuploid
- **C.** Autopolyploid
- **D.** Heteroployploid

## Answer

Option A

## Explanation

Interspecific hybridization and allopolyploidy: Creating a new fertile allopolyploid species through interspecific hybridization: Step 1: Cross two different species (Species A × Species B) → Sterile F1 hybrid (diploid, 2n) • Sterile because chromosomes from different species cannot pair properly during meiosis. Step 2: Rare spontaneous events produce UNREDUCED gametes (diploid gametes instead of haploid) due to meiotic failure. Step 3: Fusion of two such unreduced gametes → ALLOPOLYPLOID with chromosome sets from BOTH species. • Now can undergo meiosis normally (each chromosome has a homologue from the same species set). • Fertile, but reproductively ISOLATED from both parental species (different chromosome numbers). Historical example: Raphanus (radish, n=9) × Brassica (cabbage, n=9) → Raphano-brassica (2n=36, allotetraploid). This is the dominant speciation mechanism in plants (polyploidy). Answer: Interspecific hybridization → sterile diploid; unreduced gametes → fertile allopolyploid (chromosomes from both species).

Source: https://mypyqbuddy.com/questions/a-haploid-sperm-from-one-species-and-a-6a104cd5920734408bc0c764