ReasoningModerate1 mark
6(a)
In Mendel’s experiments, tall pea plants (T) are dominant over dwarf pea plants (t).
Draw a Punnett square board to show the gametes and offspring when both the parents are heterozygous for tallness.
Topic: Punnett square — Tt × Tt
Previous-year question practice database
Answer
Exam answer
PARENTS: Tt × Tt Gametes: T, t and T, t
PUNNETT SQUARE T t T TT (tall) Tt (tall) t Tt (tall) tt (dwarf)
OFFSPRING: 1 TT, 2 Tt, 1 tt — that is, THREE TALL plants to ONE DWARF.
Explanation
Set the working out fully — parents, gametes, then the square — because marks are given for the method as well as the result.
Write the gametes of one parent along the TOP and those of the other down the SIDE, then fill each box by combining the two letters that meet there.
Label each box with its PHENOTYPE as well as its genotype (tall or dwarf), since that is what makes the 3:1 ratio visible at a glance.
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