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ICSE Question Bank
2017Q1(f)(iii)Genetics – Some Basic Fundamentals
AnalogyEasy1 mark
1(f)

Given below are groups of terms. In each group the first pair indicates the relationship between the two terms. Rewrite and complete the second pair on a similar basis. Example: Oxygen : Inspiration :: Carbon dioxide : Expiration

TT : Homozygous :: Tt : __________

Topic: Heterozygous

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Answer

Exam answer

HETEROZYGOUS (hybrid).

Explanation

The relationship is GENOTYPE : THE NAME FOR THAT CONDITION.

HOMO- means SAME: TT or tt, two identical alleles. Also called PURE. HETERO- means DIFFERENT: Tt, two unlike alleles. Also called HYBRID.

THE POINT THAT MATTERS: a TT plant and a Tt plant LOOK IDENTICAL, because T is dominant and masks t. Same PHENOTYPE, different GENOTYPE.

That is exactly why a recessive character can vanish in the F1 generation and reappear in a quarter of the F2 — and why a 3:1 phenotypic ratio corresponds to a 1:2:1 genotypic ratio.

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