Interactions Between Genes and the Environment

Genes are not the only thing that can affect the appearance of an organism, environment can play a large part. Cloned plants have shown huge variation in phenotype when exposed to different environmental conditions. We can see how the environment affects a number of animal species also. However, it is not as easy to see the impact on animal as it is on plants because of the ethical aspects of producing large numbers of cloned, identical organisms for testing.

Examples of environmental impact Temperature The sex of some animals is influenced by the temperature at which their eggs are incubated. E.g. Turtles, crocodiles, and alligators. Sometimes, high temperatures produce males and low produce females, sometimes it is the other way around.

Colour Pointing In some breeds of cats and rabbits, a dark pigment is produced in cooler areas of the body, changing the colour of the fur. This is caused by a gene mutation.

The Effect of Other Organisms Daphnia will grow a large helmet when predators are near, this is usually in response to a chemical released by the predator. This helmet will allow the daphnia to defend itself from attack.

Genes and Environment in Humans Monoamine Oxidase A This is an enzyme which breaks down monoamines eaten in our food. It also breaks down neurotransmitters which affect our mood. Too much MAOA Breaks down too many neurotransmitters Depression/ aggression/ risk- taking Too little MAOA Not enough neurotransmitters broken down Depression/ addictive behaviour/ alcoholism

It has been suggested that some racial groups have a genetic tendency towards high or low levels of MAOA (New Zealand Maori’s), but there is some evidence to suggest environment can have an effect. Particularly the amount of stress a person experiences.

Cancer Cancer is caused by cells that divide rapidly and out of control. Cells do this when their DNA is damaged so it can’t be replicated efficiently. There are a number of environmental factors that can damage the DNA in cells. Environmental factors can increase the chances of cancer causing mutations occurring.

Ionising radiation Asbestos Tar in cigarette smoke

There is a well established link between exposure to UV light in sunlight and incidences of skin cancer. As holidays abroad became more popular, more people were suffering from sun burn in order to get a sun tan. Cases of melanoma skin cancer have risen steadily with the popularity of holidaying abroad. UV light damages skin cells, mutating their DNA and causing skin cancer.

People with lighter skin are more at risk of developing melanoma because the melanin in darker skin acts as natural barrier to UV light. As a consequence, incidences of skin cancer are higher in countries such as UK, USA, and Australia. People here are encouraged to cover their skin and wear sunscreen to protect themselves from UV light.

Questions Answer questions 1-5 on page 195 of your text book