Transcript A-4 Notes
Science 9: Unit A – Biological Diversity Topic 4: Wearing Your Genes Heredity and Genetics • Heredity is the passing of heritable traits from parents to offspring. Genetics is the study of heredity in species. • Variation in a species takes two forms: Continuous Variations • Continuous Variation – There is a gradual difference in a certain heritable trait between individuals. Skin color, hair color, height, etc. show continuous variation as they show a range of possibilities. Discrete Variations • Discrete Variation – This is a trait that is either one possibility or another. Being left or right handed is an example of discrete variation. Being male or female is another example, so is your blood type. Dominant and Recessive Traits • Certain traits are dominant and others recessive. Why? Dominant traits tend to be more adaptive than recessive traits. • You get two set of genes when you are gestating: one from your Mom and the other from Dad. The dominant trait always wins out and you will have that trait. How do People get recessive traits? • For example curly hair is a dominant trait. If your mother passes the gene for curly hair and your father passes his gene for straight hair, you will have curly hair. • So how do people still have recessive traits? The only way you can have a recessive trait such as lighter hair is by having been given two recessive genes. • Eg. blonde haired kids have received two blonde hair genes. Why do recessive traits still exist? • Why haven’t dominant traits taken over all over the world? Because human populations were separated from each other for most of history. Germans were allowed to evolve to their environment, and Asians to theirs. Only recently have we started to live in mixed populations. Nature Vs. Nurture • While some traits such as eye color are completely heritable, others such as scars are determined by our experience and environment. Still others, such as height, intelligence, and weight result from a complex combination of nature (your genes) and nurture (your environment or experience). Nature Vs. Nurture • Many geneticists are trying to find out how much of our mixed traits are from nature and how much from nurture. This has led to certain people becoming very sensitive and angry about the findings. Nature Vs. Nurture • Scientists have determined that intelligence is about 60% inherited and 40% due to your experience. This ratio of 60/40 is also true (roughly) for your personality type. • Some people feel that this will give employers an excuse to fire people if they don’t have the ‘right’ genetics. • The bottom line is that there is a lot that we do not yet know about genetics. Mutations = changes in our genetic material. • Mutations are changes to your genetic material. Before you are born, your genes mutate on their own, increasing variability in our species. Most of these mutations are harmless, a smaller amount is very harmful, and a tiny number of mutations can lead to a successful structural or behavioural adaptations. Mutations Cause Cancer • Mutations can also occur during our lifetime. Cancers are the result of our cells mutating and then reproducing out of control, killing and starving our healthy cells. 1 out of 3 people will develop a cancer. Mutagens Cause Mutations • Mutagens are forms of radiation and chemicals which can cause our cells to mutate (and therefore can lead to cancer). UV rays, X rays, and other high energy EM waves can mutate our cells, while chemicals in the environment or in our food can cause mutations.