Paper 3 · June 2017 · Inheritance and Variation
Discontinuous variation arises because the character is
Acontrolled by many genes acting together, each of which has a small additive effect on it.
Bdetermined almost entirely by the environment the individual grows in.
Ca quantitative character measured on a continuous scale of values.
Dcontrolled by one or a few genes, so the alleles give a small number of distinct classes.
Explanation
Where a character depends on one gene or a very few, each genotype produces a clearly different phenotype and individuals fall into separate classes with nothing in between, as with the ABO blood groups or the ability to roll the tongue. The environment has little influence on such a character. Many genes of small additive effect, with the environment acting on top of them, is what produces continuous variation instead.
Derived from ZIMSEC Biology Paper 3, Jun 2017, Q23