Selective Breeding Progress indicators Good progress Identify why
Selective Breeding Progress indicators Good progress: • Identify why humans selectively breed plants and animals. • Describe the process of selective breeding and give examples. Outstanding progress: • Explain the benefits and risks of selective breeding in plants and animals. Do now activity: 1. What are some examples of characteristics you have inherited vs. characteristics caused by the environment? 2. Explain the difference between continuous and discontinuous data, give an example for each. 3. What do you think selective breeding might be? Why might humans use this method of breeding?
For many hundreds of years farmers have used selective breeding to ensure that they get the characteristics of animals and plants that they want. THINK > PAIR > SHARE: Can you identify any particular characteristics that farmers might find favourable in the following organisms:
Task: Watch the video and answer the following questions: https: //www. youtube. com/watch? v=f. HS-OY 9 XDZc 1. What is selective breeding? 2. Describe how selective breeding works 3. The process can be used to select for a whole range of features, state four examples. 4. What are some disadvantages of selective breeding or the organisms?
Self-assessment: 1. Selective breeding is when humans breed plants and animals for particular genetic characteristics 2. Organisms with the desired traits from a mixed population are selected and bred together. The offspring with the desired characteristics are then bred together, eventually all of the offspring will show the desire characteristic. 3. Examples include disease resistance in crops, animals that produce more meat or milk, domestic dogs and farm animals with a good temperament, large or unusual flowers. 4. Organisms that are interbred can lead to a higher chance of genetic disorders being inherited, a smaller gene pool also means that the organisms have a lower chance of adapting if their environment suddenly changes.
How does selective breeding work? Task: Below are lots of breeds of dogs, choose two dogs to selectively breed together to get the characteristics in a dog that you would like. Draw a flow diagram to show this process happening and sketch the dogs you have selected as well as the possible offspring they produce:
Task: Complete the worksheet on selective breeding
Self-assessment: 1. a) ISA brown b) Sussex c) This chicken is able to cope with living in the cold and has the second highest amount of eggs produced per week d) 156 e) Temperature f) Hamburg g) Because they can be quite aggressive h) Put egg size to the top so that they see that Sultan eggs produce large eggs, remove ISA Brown from the table to then the Sussex would be the better option. 2. So that they are able to produce eggs more quickly and once they are fully grown they can eventually be sold for meat. 3. Genetic engineering
Problems with selective breeding Selective breeding can greatly reduce the number of alleles in a population, as only those with the desirable alleles interbreed. This greatly reduces the variation within a population. If the environment changes – new predator, lack of food, climate change – the lack of variation means that none of the organisms may be able to adapt to cope with this change, which can result in the population dying out. Another problem is interbreeding, when organisms mate with organisms that are very closely related to them it can result in an accumulation of recessive traits. This can lead to certain breeds being prone to particular diseases. For example, boxer dogs are at high risk of epilepsy. Quick Check: 1. Explain why selective breeding reduces variation in the alleles of a breed of animals or plants (3 marks) 2. Explain why variation is useful in a population (3 marks) 3. Discuss the dangers of reducing the genetic variation in a population (3 marks)
Self-assessment: 1. Selective breeding can lead to a reduction in variation as only the individuals containing a set of allele/alleles will be chosen to breed together. This results in offspring that are very similar to each other as they contain a very closely related set of genetic information. 2. Variation is useful to a population as it enables a population to deal with a change in their environment more easily. If there a change, for a example a new disease or predator or lack of a food source, organisms will need to adapt to cope with this change. If all organisms are the same then they will all struggle to adapt to this new environment and would be at risk of dying out. 3. The dangers of reducing genetic variation is that organisms would find it more difficult to adapt and cope with a changing environment and also it would be make it more likely that genetic disorders will arise. If there is an accumulation of recessive alleles this can lead to a higher prevalence of genetic disorders for a certain breed.
Plenary ~ Summarise what you have learnt this lesson in three sentences. Include some of the following key words in your summary: Genetic Alleles Selective Breed Organisms Dogs Cows Crops Characteristics Desirable
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