Combination of both: environmental influence example: (alcohol during pregnancy) Fetal alcohol spectrum disorder (fasd) or fetal alcohol syndrome (fas) Growth retardation, characteristic facial features, central nervous system anomalies, (brain growth/damage) intellectual impairment. Fasd is shown in mother with chronic heavy alcohol use/frequent use during pregnancy. Many factors affect fasd, including alcohol metabolism. Alcohol dehydrogenase breaks down alcohol (genetic factor?: genetic factor example: Areas of the brain degenerate due to a toxic protein that is produced when there is a mutation. Gene coding for huntington disease is on chromosome 4- normal repeat of 35 cag codons. If there is a repeat of more than 42, produces toxic protein: combination of both: (most common) Colour of fur of the arctic fox. This is due to heat sensitive genes controlling the colour of the fur. The colour of the petals change depending on the ph of the soil. In acidic environment, the colour is blue, pink in alkaline.