NECO 2008 Biology · Question 7

What will the phenotypic ratio when a tall pea plant (TT) is crossed with a short pea plant (Tt)?

Options

A.0:04
B.1:03
C.2:02
D.3:01
E.4:00

Answer: E. 4:00

Explanation written with AI and checked against the answer key

Analyze the question: We're crossing TT (tall) with Tt, which the question calls "short." We need the phenotypic ratio of the offspring. Concept: In Mendelian genetics, T (tall) is dominant over t (short). A plant with the genotype Tt is tall, because the dominant allele masks the recessive one. Only tt is short. Step-by-step solution: Parent 1 (TT) gametes: T, T Parent 2 (Tt) gametes: T, t Punnett square: | | T | t | |---|---|---| | T | TT | Tt | | T | TT | Tt | Genotypes: 2 TT : 2 Tt (1:1) Phenotypes: TT is tall and Tt is tall, so all 4 offspring are tall. Phenotypic ratio: 4 tall : 0 short, or 4:0. Note on the question wording: Tt is not truly "short." It is a heterozygous tall plant. If the question really meant a short plant, the genotype would be tt, and TT × tt would give all Tt (still 4:0 tall). Answer: E (4:00) Tip: If one parent is homozygous dominant (TT), every offspring gets at least one T, so all of them show the dominant phenotype. Whenever you see TT × anything, expect a 100% dominant phenotype.

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