Theory question 106
Crop Improvement(a) Define the term hybridization.
(b) State five aims of crop improvement.
(c) Describe a mono-hybrid cross as explained by Mendel's law of segregation. Illustrate your answers with clearly labelled diagrams.
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(a) Hybridization is the crossing of two genetically different plants (varieties or species) to combine their desirable characters in the offspring
(b) Any five: higher yield; resistance to pests and diseases; better quality (taste, nutrients, keeping quality); adaptation to climate/soil (drought tolerance); early maturity; uniformity and suitability for mechanisation; better response to fertilizer
(c) Cross pure tall (TT) with pure dwarf (tt) pea plants; gametes T and t; F1 all Tt (tall, T dominant); selfing F1 (Tt × Tt) gives gametes T, t from each parent; F2 genotypes TT, Tt, Tt, tt in ratio 1:2:1; phenotypes 3 tall : 1 dwarf. This shows that the pair of factors separate (segregate) at gamete formation. Diagram: labelled parents, gametes, F1, checkerboard/F2
Use labelled cross diagrams with genotypes and ratios.