Theory question 104
Variation(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.
Show the model answer
(a) The differences in features (structure, function, behaviour) between members of the same species, which may be inherited or caused by the environment.
(b) Any five: produces new varieties; allows natural selection (survival of the best-adapted); some individuals resist diseases; population can adapt to environmental change; reduces competition by using different resources; allows breeders to select desired traits; helps identification (fingerprints, blood groups).
(c) Table — Continuous: shows a range of intermediate forms / Discontinuous: clear-cut groups with no intermediates; Continuous: controlled by many genes (polygenic) / Discontinuous: one or few genes; Continuous: strongly affected by environment / Discontinuous: little or not affected; Continuous: gives a normal distribution curve / Discontinuous: bar chart of distinct classes; Continuous: e.g. height, weight / Discontinuous: e.g. blood group, tongue rolling. (Answer must be in a table.)
(d)(i) Characters whose genes are carried on the sex chromosomes (usually the X), e.g. haemophilia, colour blindness, so they show different patterns in males and females.
(ii) Both alleles in a heterozygote are fully expressed, neither dominant, e.g. AB blood group or roan coat in cattle.
(iii) The increased vigour, yield or disease resistance of offspring from crossing two genetically different (unrelated) parents.
Part (c) earns no marks unless it is in a table.