Theory question 104
Mendelian Inheritance(a) Explain briefly the following terms: (i) gene; (ii) hybrid; (iii) trait. (b) Two heterozygous yellow flowers are crossed. Using a genetic diagram; state the phenotypic and genotypic ratios of the first filial generation. (c) State four transmittable characters in plants.
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(a)(i) A gene is a unit of heredity, a section of DNA on a chromosome that controls one characteristic.
(ii) A hybrid is the offspring of parents that differ genetically (e.g. of two different varieties or species); a heterozygous individual.
(iii) A trait is a characteristic or feature of an organism that can be inherited, e.g. flower colour.
(b) Let Y = yellow (dominant), y = other colour (e.g. white). Parents: Yy × Yy; gametes: Y, y and Y, y; F1: YY, Yy, Yy, yy.
Genotypic ratio 1 YY : 2 Yy : 1 yy.
Phenotypic ratio 3 yellow : 1 non-yellow (white).
(c) Any four: height (tall/dwarf); flower colour; seed colour; seed shape (round/wrinkled); pod shape or colour; position of flowers; leaf shape; fruit colour; disease resistance.
Show parents, gametes, fusion and offspring in the genetic diagram.