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2020Q1(b)(iv)Genetics – Some Basic Fundamentals
DefinitionModerate1 mark
1(b)

Explain the following terms:

Phenotype

Topic: Phenotype

Previous-year question practice database

Answer

Exam answer

The PHENOTYPE is the observable or external appearance of an organism — the visible expression of its genes for a particular character.

Explanation

The essential word is OBSERVABLE — what you can SEE.

THE PAIR must be given together to be clear: GENOTYPE — the alleles an organism CARRIES (TT, Tt, tt) PHENOTYPE — how it LOOKS (tall, dwarf)

The relationship between them is the point of the whole chapter: TWO DIFFERENT GENOTYPES CAN GIVE THE SAME PHENOTYPE. TT and Tt both look tall, because T is dominant and masks t. That is exactly why a recessive character can vanish in F1 and reappear in F2 — and why a 3:1 phenotypic ratio corresponds to a 1:2:1 genotypic ratio.

Example

Example: for height in a pea plant, the phenotypes are TALL and DWARF. Both TT and Tt plants have the phenotype "tall".

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