B14: Variation and evolution

Question 1

What is reproduction??

Answer 1

All the differences in the characteristics of individuals in a population.

Question 2

What are the 3 main causes of variation?

Answer 2

Inherited alleles (genetic causes e.g. hair and eye colour).
Environmental causes (e.g. the colour of flowers based on the pH of soil or language spoken).
Combination of genes and environment (e.g. height, some people have alleles which make them more likely to grow taller, however a diet in calcium also contributes to this).

Question 3

What is another cause of genetic variation?

Answer 3

Mutations (random changes in DNA, most have no effect on phenotype).
Very rarely, a mutation can lead to a new phenotype, sometimes it may be beneficial if the environment changes, which can lead to a rapid change in species.

Question 4

When did life first develop on Earth?

Answer 4

3 billion years ago - first life forms were very simple e.g. single cells. All living species have evolved from these cells - this is called evolution by natural selection.

Question 5

What is natural selection?

Answer 5

Rabbits example:
All rabbits have slightly different alleles e.g. some have thicker fur, better hearing etc. When a change is made to the environment, e.g. it gets colder, the rabbits with thicker fur will have a survival advantage, meaning more of them will survive and reproduce, which increases the populations of rabbits with thicker fur.

Question 6

What is evolution?

Answer 6

The change in the inherited characteristics of a population over time through a process of natural selection.

Question 7

What happens when the phenotype of the same species becomes too different?

Answer 7

They can no longer interbreed, the two populations have now become separate species.

Question 8

What are the 4 examples of selective breeding?

Answer 8

Domestic dogs - selectively bred to have a gentle nature.
Food crops e.g. wheat - selectively bred to be resistant to disease.
Animals e.g. cows have been selectively bred to produce more meat or milk.
Certain plants - to produce large or unusual flowers.

Question 9

How is selective breeding carried out?

Answer 9

E.g. cows to produce more meat.
Take a mixed population of cows and select the largest male and female and breed them. Sexual reproduction produces variation in offspring, so offspring will be a mixture of larger animals and smaller animals - select largest male and female offspring and breed them together. Continue doing this over many generations until all offspring are large

Question 10

What is the issue with selective breeding?

Answer 10

If we breed together closely related animals or plants it results in inbreeding. This causes some breeds to be prone to disease or inherited defects e.g. dogs have been selectively bred for generations, and many breeds have developed inherited disorders like heart disease or epilepsy.

Question 11

What is genetic engineering?

Answer 11

When genes from one organism are cut out and transferred to cells of a different organism. e.g. the genome of a bacteria can be modified and now includes a human gene.

Question 12

How can insulin be made using genetic engineering?

Answer 12

Bacteria can be genetically modified to contain the human insulin gene (good for people with Type 1 diabetes who cannot produce their own insulin). They now produce insulin, which can be purified and used for diabetes.

Question 13

Why are genetically modified (GM) crops be made?

Answer 13

They produce a greater yield than normal crops.
Can be resistant to disease or insect attack.
Produce bigger/ better fruits.
Some are resistant to herbicides/ pesticides, meaning farmers can spray them to kill weeds without harming the GM crop.

Question 14

What are the issues with GM crops?

Answer 14

Some people question whether they are safe.
Not enough research has been done on health effects.
People question whether they could be harmful to insects/ wild flowers

Question 15

What can genetic modification be used for?

Answer 15

Making insulin producing bacteria
GM crops
Gene therapy

Question 16

What is gene therapy?

Answer 16

Using genetic modification to treat inherited disorders in humans.
Dis - unknown long term effects (unknown potential effects on other genes)

Question 17

What are the main steps in genetic engineering?

Answer 17

Identify gene that you want to transfer e.g. a human gene or a gene from a plant.
Add enzymes to isolate the gene.
Transfer gene to plasmid, a small circle of DNA which come from bacteria (useful for transferring DNA from one organism to another). A virus can also be used, as both plasmid and virus transfer DNA from one organism to another, they are vectors.
Finally, the desired gene is transferred into the cells of the target organism, like an animal, plant or microorganism like a bacterium.
The gene is always transferred at the early stage of the organism’s development, like the early embryo stage. This is to make sure all the cells receive the transferred gene, that way the organism develops with the characteristic that we want.

Question 18

What are the methods used to clone plants?

Answer 18

Cuttings
Tissue-culture

Question 19

What is the advantage of cloning plants?

Answer 19

Because the plant has the same characteristics as its parent plant, we know exactly what characteristics it will have e.g. colour of flowers.

Question 20

Describe cloning by taking cuttings

Answer 20

Old method. Works better if we want a few clones from a plant.
A small piece of the plant is removed at the end and then dipped into rooting powder, which contains plant hormones that encourage the plant to develop roots.
By taking cuttings, we produce genetically identical clones of the started plant.

Question 21

Describe the process of tissue culture

Answer 21

Take the plant you want to clone - divide it into hundreds of tiny pieces. These small groups of cells are then incubated with plant hormones which stimulate the plant to grow and develop.
Conditions - sterile to prevent growth of bacteria or fungi.

Question 22

What are the benefits of tissue culture?

Answer 22

Useful in commercial plant nurseries - allows growers to produce thousands of genetically identical plants quickly and cheaply.
Gardeners can be certain that they will get the characteristics they want because plants are clones.
Preserves rare species of plants.

Question 23

Describe the process of cloning animals

Answer 23

e.g. horses.
Start with sperm and egg from horses with desirable characteristics - fertilisation produces a fertilised egg. Allow the fertilised egg to develop into an early stage embryo (important that the cells in the embryo have not started to specialise). Use a glass rod to split embryo into 2, finally transplant 2 embryos into 2 host mothers. The embryo will then develop and grown into two identical offspring.

Question 24

What are the issues of embryo transplants?

Answer 24

Cannot be certain that the offspring will have the characteristics we want, because we start with sperm and egg - can be overcome using adult cell cloning.

Question 25

Describe the process of adult cell cloning

Answer 25

e.g. sheep
Start by removing a cell from the sheep that we want to clone (e.g. skin cell). Remove nucleus from the cell - it contains genetic information from the animal we are cloning. Take an unfertilised egg cell from the same species (any female sheep), the remove nucleus and throw it away. Insert the nucleus from the original adult body cell into the empty egg cell. Then give the egg cell an electric shock, making the egg cell divide and produce an embryo, containing the same genetic information as the adult skin cell we started with. When the embryo has developed into a ball of cells, its inserted into the womb of an adult female to continue development.

Question 26

What is the benefit of adult cell cloning?

Answer 26

Cloning from an adult - we know the characteristics that the clone will have