page 13 19. Breeding programmes can be used to increase starch levels in barley plants. This involves breeding closely related plants with high starch levels for several generations. This is carried out in order to A increase the frequency of homozygous deleterious alleles B reduce the frequency of homozygous deleterious alleles C increase the frequency of heterozygotes D reduce the frequency of heterozygotes. 20. The bar chart shows the percentage decrease in yield of four crops as a result of the effects of weeds, fungi and insect pests. Key weeds fungi insect pests decrease in yield (%) crop D C B A 40 35 30 25 20 15 10 5 0 Predict which crop will show the greatest increase in yield if herbicides and insecticides are applied. [Turn over