(a) What is variation?
(b) State five advantages of variation within a species.
(c) In a tabular form, outline four differences between continuous and discontinuous variations.
(d) Explain the following terms:
(i) Sex-linked characters
(ii) Co-dominance
(iii) Hybrid vigour
Explanation
(a) Variation: These are morphological; and physiological differences; which occur within a species which could be hereditary or acquired from the environment.
(b) Advantages of variation: – Appearance of new varieties – variation allows survival of the fittest – competition arises – nature selects the most adapted varieties – that are more resistant to diseases – and better adapted to changes in the environment.
(c) Differences between continuous and discontinuous variation
| continuous | Discontinuous |
| caused by co-dominance | caused by complete dominance |
| Intermediates are present | No intermediate characteristic |
| Affected by the environment | not affected by the environment |
| They are controlled by genes /polygenes | Not polygenic |
| Follow the normal distribution curve/frequency of characteristics evenly distributed | Not evenly distributed |
(d)(i) Sex-linked characters: These are characteristics associated with the sex of an individual; the gene for the expression of the character; is borne on one of the sex/the X chromosomes.
(ii) Co-dominance: This is a condition in a heterozygote; in which both alleles have equal dominance; and the phenotype is a mixture of the opposing characters.
(iii). Hybrid vigour: This is the production of new varieties within a species; which are healthier/have greater resistance to diseases/are better adapted to the environment; as a result of out breeding/crossing non related members of a species.