Q1. [3] deep thorough-understanding
In Mendel's dihybrid cross, F1 plants with round yellow seeds (RrYy) were self-pollinated. Among the F2 offspring, two phenotypic classes — round green seeds and wrinkled yellow seeds — were not present in either parent. (i) Explain the biological mechanism that produces these new combinations. (ii) What does the appearance of these new combinations tell us about the inheritance of seed shape and seed colour relative to each other?
Generated by claude-sonnet-4-6 · 2026-06-26 01:03 · grounding rag
Model Answer
(i) In the F1 plant (RrYy), during gamete formation, the factors (genes) for seed shape (R/r) and seed colour (Y/y) separate independently and recombine randomly to form zygotes. This produces new combinations like Rryy (round green) and rrYy (wrinkled yellow) that were absent in the parents. These new trait combinations arise because factors controlling seed shape and seed colour recombine freely during fertilisation to form F2 offspring.
(ii) The appearance of these new combinations shows that seed shape and seed colour are independently inherited — the inheritance of one trait does not influence the other.
Source: Chapter 8, Section 8.2.2
---
Explanation
- (i) The key phrase from the textbook is: "factors controlling for seed shape and seed colour recombine to form zygote leading to form F2 offspring." Examiners want: independent separation of factors during gamete formation + random recombination at fertilisation.
- (ii) The exact conclusion from the textbook is: "the tall/short trait and the round seed/wrinkled seed trait are independently inherited." Use this language directly — it scores full marks.
- Avoid over-explaining meiosis; at Class 10 level, "factors separate and recombine independently" is sufficient.