(a) List five aims of crop improvement (b) Define the term selection in crop improvement. (c) List three methods of selection. (d) Explain the following gen...

(a) Five aims of crop improvement:

1. To increase crop yield per unit area.
2. To produce varieties that are resistant to pests and diseases.
3. To produce varieties that are tolerant of adverse conditions such as drought and poor soils.
4. To improve the quality of produce (for example higher nutrient, oil or protein content).
5. To produce early-maturing varieties and improve other desirable characters such as ease of harvesting and better market qualities.

(b) Selection. Selection in crop improvement is the process of choosing and keeping plants (or seeds) that have desirable characters, such as high yield or disease resistance, for propagation, while rejecting and discarding the undesirable ones.

(c) Three methods of selection:

1. Mass selection.
2. Pure-line selection.
3. Pedigree selection (progeny selection).

(d) Genetic terms:

• (i) Homozygotes: individuals that carry two identical alleles of a gene for a particular character (for example TT or tt); they breed true for that character.
• (ii) Back cross: a cross between an F₁ offspring (a hybrid) and one of its parents (or an individual genetically identical to a parent); a cross with the homozygous recessive parent is a test cross used to find the genotype of the offspring.
• (iii) Dominance: the condition in which one allele (the dominant allele) masks or suppresses the expression of its partner (the recessive allele) in a heterozygote, so that only the dominant character is shown in the individual.