Sources of genetic variationEdexcel A-Level Biology B: Mind map

Exam questions on Sources of genetic variation

1. An orchard owner notices one branch of an apple tree bearing red apples while the rest of the tree bears green apples. Cuttings taken from the red branch and grown into new trees all produce red apples. Genetic testing shows a new allele for fruit colour is present in every cell of the red branch.
   Explain why every tree grown from a cutting of the red branch produces red apples.2 marks
2. A species of beetle has a diploid number of 8 (four pairs of homologous chromosomes). A breeder wants to know how many genetically different offspring two unrelated beetles could produce. Ignore crossing over unless told otherwise.
   Two unrelated beetles of this species mate. Calculate the number of genetically different zygotes that random fertilisation could produce from their gametes, ignoring crossing over.2 marks
3. Two parents who are both heterozygous at many gene loci have four children. No two of the children, apart from any identical twins, would be expected to have the same genotype, even though all of the children have the same two parents.
   Explain how meiosis produces gametes that differ genetically from each other.3 marks