Environmental factors, internal and external, can influence gene expression by affecting levels of regulatory proteins or transcription factors. Environmental factors explain the differences observed between identical twins, even though they have the same DNA.
Scientists have investigated a range of phenotypic traits, such as intelligence, in twins. Data has been compared between identical and non-identical twins to help determine whether these characteristics are genetic or more greatly influenced by the environment. The graphs below shows data comparing identical and non-identical twins and their IQ.
Suggest conclusions that could be drawn from the data shown in the graphs.
The scientists also investigated how many hours per night identical and non-identical twins typically sleep. The results are shown in the graph below. The scientists concluded that sleep was not a heritable factor and environmental factors caused differences in sleep time.
