Genotype, environment and epigeneticsEdexcel International A Level Biology: Mind map

Exam questions on Genotype, environment and epigenetics

1. A gardener takes cuttings from a single hydrangea plant and grows them in two sets of pots. One set is in acidic soil and produces blue flowers. The other set is in neutral soil and produces pink flowers. All the cuttings receive the same light and the same amount of water.
   Explain how genetically identical plants can have different phenotypes.2 marks
2. Researchers compared the DNA of identical twins at age 5 and at age 60. The base sequences of the twins' DNA were identical at both ages. At age 60, however, the pattern of methyl groups attached to cytosine bases in their DNA differed between the twins, and the twins differed in several features of their health.
   Explain why identical twins can show differences in phenotype even though their DNA base sequences are identical.2 marks
3. In the nucleus of a liver cell, DNA is wound around histone proteins. A gene for an enzyme that is needed only in the kidney is switched off in the liver cell. Analysis shows that the histones associated with this gene have had acetyl groups removed, and that cytosine bases in the promoter region of the gene carry methyl groups.
   Explain how these modifications prevent the gene from being expressed in the liver cell.3 marks