(a) What is variation? (b) State five advantages of variation within a species. (c) In a tabular form, outline four differences between continuous and disco...

(a) Variation is the differences in characteristics (structural, physiological or behavioural) that exist among individuals of the same species, or between the offspring and their parents.

(b) Five advantages of variation within a species

• It enables some members of the species to survive changes in the environment (adaptation and survival of the fittest).
• It provides the raw material for natural selection and evolution, leading to the formation of new species.
• It enables the species to resist diseases and pests, since some individuals will be resistant.
• It allows the species to colonise and exploit different or new habitats.
• It makes selective breeding and improvement of crops and livestock possible by choosing desirable individuals.

(c) Differences between continuous and discontinuous variation

(d) Explanation of terms

• (i) Sex-linked characters: characters whose controlling genes are carried on the sex chromosomes (usually the X chromosome) and are therefore inherited along with sex; they appear more often in one sex (mostly males), for example colour blindness and haemophilia.
• (ii) Co-dominance: a condition in which two contrasting alleles of a gene are both fully expressed in a heterozygote, so neither is dominant over the other, for example the AB blood group where both A and B antigens show, and roan colour in cattle.
• (iii) Hybrid vigour (heterosis): the increased strength, size, yield, fertility or vigour shown by the offspring (hybrid) of a cross between two genetically different (pure-breeding) parents, which is greater than that of either parent.