Inheritance Genetics and Society G Davidson

Selective Breeding Many people are concerned with breeding animals and plants. Because variation exists between members of a species, man has selected organisms for breeding in the hope that the “good” characteristics are passed on to the next generation. E.g. farmers are always trying to improve their stock or their crops.

e.g. racehorses

Selective Breeding Dairy farmers trying to increase yield. Beef farmers trying to increase mass. Sheep farmers trying to produce better quality wool. Crop farmers trying to increase yield. Examples include At the same time, “quality” is also extremely important.

e.g. flower growers.

Mutations Almost 1% of all babies born today have some sort of changes to their chromosomes. These changes are called MUTATIONS. They can produce changes in the characteristics of an organism. The affected organism is said to be a MUTANT.

Amniocentesis This is the removal of amniotic fluid for medical examination. A sample of the cells in the fluid can be studied. If an abnormality is detected, the parents may decide to have the pregnancy terminated e.g. Down’s Syndrome.

Amniocentesis

Down’s Syndrome Extra chromosome indicates Down’s syndrome.

Useful Mutations Most mutations are not useful to man and lead to the formation of inferior phenotypes. There are some mutations that are useful, and these are encouraged. E.g. some plants possess extra sets of chromosomes as a result of chromosome mutations. These plants are called Polyploids, and can show stronger growth.

Extra sets of chromosomes occurring in fruit such as apples, pears, strawberries, etc. can lead to increased fruit size and increased yield – but the quality is just as important.

In some crops such as bananas, grapes, water melons, etc.. Mutations prevent the formation of seeds.

In barley a mutation produces plants which are upright when ripe. This is called Midas Barley and shows fewer losses during combine harvesting. A mutation in sheep results in animals with very short legs. This means the walls & fences keeping them in can be lower. Other examples include:

Influencing the Rate of Mutations Mutations can be induced by mutagenic agents. E.g. radiation such as atomic, X-rays, Ultra-violet, etc… E.g. chemicals such as mustard gas, colchinine, etc.. Dividing cells can be affected causing diseases, e.g. leukaemia.