Скачать с ютуб Selective Breeding | 9-1 GCSE Science Biology | OCR, AQA, Edexcel в хорошем качестве

Selective Breeding | 9-1 GCSE Science Biology | OCR, AQA, Edexcel

https://goo.gl/CBJtqt to unlock the full GCSE Biology & Combined Science videos series for the new 9-1 OCR, AQA and Edexcel specifications. They key points covered in this video include: 1. What is selective breeding? 2. The process of selective breeding 3. Uses of selective breeding 4. Risks of selective breeding What is Selective Breeding? Selective breeding, or artificial selection, is the process of choosing to breed 'the best' plants or animals so that genes for desired characteristics remain in the population. Humans have done this for thousands of years by breeding food crops from wild plants and domesticating animals (e.g. cows, dogs etc.) The Process of Selective Breeding Let’s look at the five steps involved in selective breeding. 1. Decide what characteristics are desirable. 2. Select organisms with these characteristics from a mixed population. 3. Breed these individuals together. 4. Select the best offspring, and breed them together. 5. Repeat this for many generations until all offspring have the desired characteristics. Uses of Selective Breeding Examples of desired characteristics which can be selectively bred for include: Crops with resistance to particular diseases. Crops that are easy to harvest and therefore generate higher yields. Animals that produce milk or meat at high quantities. Domestic animals that are gentle/loving. Flowers that can be used decoratively (e.g. larger, have vibrant colours or an unusual shape). Risks of Selective Breeding There are two big problems with breeding closely related organisms (known as 'inbreeding'): 1. It reduces the gene pool - this is the number of alleles (versions of a gene) of a species. This means there is less variation within a population so when a new disease appears, there is a smaller chance that some organisms will be resistant to the disease. As a result, the whole population can be wiped out, and the species may even become extinct. 2. Inbreeding also increases the chance of inheriting a genetic disease or defect - for example, inbred white tigers are often cross-eyed. This raises many ethical concerns regarding inbreeding. Summary 1. Selective breeding, or artificial selection, is the process of breeding plants and animals for particular genetic characteristics. 2. Individuals with desired characteristics are selected and bred together - this is repeated for many generations until all organisms have the desired characteristics. 3. It can be used to produce crops that easier to harvest or are disease resistant, animals that yield more milk and meat or have a gentle nature, or to produce flowers that are have an interesting appearance. 4. Inbreeding causes problems because it reduces the gene pools so diseases are more likely to wipe out the population and there is a greater chance of inheriting genetic diseases/defects.