Variation and Selection Flashcards
Why do you do selective breeding?
- Organisms are selctively bred to develop the best features uch as:
1. Maximum yield of meat, milk, grain etc.
2. Good health and disease resistance
3. In animals other qualities such as temperament, speed, fertility and god mothering skills etc.
4. In plants other qualities such as attractive flowers and nice smell etc
Describe the process of selective breeding
- Human famers select organisms with desired features
1. Decide which characteristics are important
2. From your existing stock select the ones (parents) which have the best characteristics
3. Breed them with each other
4. Select the best of the offspring and breed them together
5. Continue this process over several generations and the desirable trait gets stronger and stronger. In farming this will give the farmer gradually better and better yields
What is selective breeding also known as?
Artificial selection
How can selective breeding increase the productivity of cows?
- Cows can be selectively bred to produce offspring with e.g. a high meat yield
- First, the animals with characteristics that will increase meat yield (e.g. the largest cows and bulls) are selected and bred together
- Next, the offspring with the best characteristics (e.g. the largest) are selected and bred together
- If this is continued over several generations, cows with very large meat yields can be produced
How can selective breeding increase the number of offspring in sheep?
Farmers can selectively breed sheep to increase the number of lambs born. Female sheep (ewes) who produce large numbers of offspring are bred with rams whose mothers had large numbers of offspring. The characteristic of having large numbers of offspring is passed on to the next generation
How can selective breeding increase crop yield?
- Selective breeding can be used to combine two different desirable characteristics
- Tall wheat plants have a good grain yield but are easily damaged by wind and rain. Dwarf wheat plants can resist wind and rain but have lower grain yield
- These two types of wheat plant were cross-bred, and the best resulting wheat plants were cross-bred again. This resulted in a new variety of wheat combining the good characteristics - dwarf wheat plants which could resist bad weather and had a high grain yield
What is the traditional method of cloning plants?
Taking cuttings
- but there is a limit to how many plants you can make using this method
- the cuttings are kept damp using plastic films or special propagators
Describe micropropagation (tissue culture), which is used to clone plants
- Take a plant you want to clone
- Remove the tips of the stem and side shoots
- These are called explants
- Trimmed to about 1mm in length
- The explants are sterilised to kill any microorganisms - Explants are then grown in vitro using nutrient media (e.g. placed in an agar medium that contains nutrients and plant growth hormones)
- SHOOTS are grown and more can be taken if needed
- Explants which are growing shoots are transferred to another medium with different hormones to encourage ROOT growth
- When explants have grown roots they are transferred into a greenhouse and transported into compost
- Plants are then gradually acclimatised to normal growing conditions including a very moist atmosphere to reduce water loss
What are the advantages of micropropagation?
- Micropropagation can be used to produce commercial quantities of identical plants (clones) with desirable characteristics)
1. Large numbers of genetically identical plants can be produced rapidly
2. Species that are hard to grow in other ways can be propagated
3. Genetic modifications can be made in a small number of plants which then give thousands of plants carrying the desired change
4. Tiny plants can be stored until needed
5. Plants can be produced at any time of year
What are the disadvantages of micropropagation?
Because all plants are genetically identical they could all be vulnerable to a new disease or a change in conditions
How was Dolly cloned?
- The nucleus of a sheep’s egg cell was removed creating an enucleated cell
1. Dolly was created by taking the diploid nucleus from the udder cell of a mature sheep, and placing it in the egg cell of another sheep from which the nucleus had been removed
2. This was given a tiny electric shock, which started it dividing by mitosis, as if it was a normal fertilised egg
3. The cell developed into an early embryo
4. It was then transferred into the uterus of a foster mother where the embryo grew and developed into Dolly
What can sheep and other mammals be genetically engineered to do?
- Sheep and other mammals can be genetically engineered to produce proteins that humans need to treat diseases
- The genetically modified animals secrete the desired protein in their milk
- Once one animal had been genetically modified, it can be cloned to produce a number of identical animals, all of which will produce the desired protein in their milk
- Scientists hope that one day genetically modified mammals might be used to develop organs that could be used in human transplants without being rejected by the human immune system
Why is it easier to modify bacteria?
They are unicellular and developmentally simple
Why is it harder to modify multicellular organisms?
- Need to modify all cells usually only way to do this is modifying the zygote to make a genetically modified embryo
- Need a method of getting modified x into the cell (using a vector)
Describe the stages of cloning a sheep
- An unfertilised egg is removed from a donor sheep
- The nucleus is removed from the donor egg cell
- A small udder cell containing a nucleus is transferred to the egg cell
- Artificially formed zygote cell divides to form an embryo
- Embryo is transferred into the uterus of a foster mother sheep
- Lamb is born that is genetically identical to the “parent sheep” that donated a nucleus
