Two traits of a pea plant — seed shape (round R / wrinkled r) and plant height (tall T / short t) — are located on different chromosomes. When a plant of genotype RrTt self-pollinates, are the alleles for seed shape and plant height inherited independently or together? Explain how the physical location of genes on chromosomes determines the answer, and use a cross to support your reasoning.
Generated by claude-sonnet-4-6 · 2026-06-26 01:04 · grounding rag
Model Answer
The alleles for seed shape and plant height are inherited independently because the two genes are located on different (non-homologous) chromosomes. During gamete formation, chromosomes of each pair separate independently of other pairs (Mendel's Law of Independent Assortment), so the allele inherited for one trait does not affect the allele inherited for the other.
Cross: RrTt × RrTt (self-pollination)
Gametes produced: RT, Rt, rT, rt (each combination equally likely)
The F2 progeny show new combinations such as tall-wrinkled (R\_tt) and short-round (rrT\_), which could not arise if the traits were always inherited together. This confirms independent assortment.
Source: Chapter 8 – Heredity, Section 8.2.2
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Explanation
- The key concept is independent assortment, which applies only when genes are on different chromosomes (as stated in the question and confirmed in the passage: "the tall/short trait and the round seed/wrinkled seed trait are independently inherited").
- Examiners expect: (1) a clear statement that inheritance is independent, (2) the reason (different chromosomes → independent separation during gamete formation), and (3) evidence from the cross — specifically the appearance of new trait combinations in F2.
- Do not draw a full 4×4 Punnett square for a 3-mark question; just list gametes and mention the new combinations as proof.