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

Explain the following terms:

Allele

Topic: Allele

Previous-year question practice database

Answer

Exam answer

ALLELES are the alternative forms of the SAME GENE, occupying the same position (locus) on homologous chromosomes and controlling the same character, but expressing it in contrasting ways.

Explanation

Three elements make a complete definition: the SAME gene, the SAME position on homologous chromosomes, and CONTRASTING forms of one character. An example costs one line and secures the mark.

The terms that follow from it: HOMOZYGOUS — both alleles alike (TT or tt) HETEROZYGOUS — alleles different (Tt) GENOTYPE — the alleles present; PHENOTYPE — the appearance produced

Note that a Tt plant LOOKS identical to a TT plant, because T is dominant — same phenotype, different genotype.

Example

Example: T (tallness) and t (dwarfness) are alleles of the gene for height in a pea plant.

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