In the study of inheritance, traits can show either discontinuous (discrete) variation or continuous variation. For example, in many plant species, flower colour is a discrete trait, whereas seed mass shows a continuous range of phenotypes.
Which of the following statements correctly describes the genetic basis of these types of variation?
Continuous traits like seed mass are polygenic, meaning they are controlled by multiple genes at different loci that have an additive effect on the phenotype.
Discontinuous traits like flower colour are controlled by a single gene, and the different phenotypes arise because alleles at this locus have an additive effect.
Continuous variation is typically controlled by a single gene with many codominant alleles, which prevents environmental factors from altering the phenotype.
A cross between two individuals heterozygous for two genes that show recessive epistasis for a discrete trait will result in a phenotypic ratio of 12:3:112:3:112:3:1.
97 exam-style questions on OCR GCSE Biology 5.1 Inheritance, covering 5.1.1 The genome, 5.1.2 Environment and phenotype, 5.1.3 Variants and mutations, 5.1.4 How genetic variants influence phenotype, 5.1.5 Asexual and sexual reproduction, 5.1.6 Haploid and diploid, 5.1.7 Meiotic cell division, 5.1.8 Single gene inheritance, 5.1.9 Predicting single gene crosses, 5.1.10 Sex determination, 5.1.11 Multiple gene inheritance, and 5.1.12 Development of our understanding of genetics. Each one has a worked solution and a mark scheme showing where the marks go.