Variation

Question 1

Define variation

Answer 1

Variation are the differences in the characteristics of individuals in a population

Question 2

Causes of variation

Answer 2

due to differences in:

• the genes (Alleles) that individuals have inherited (genetic causes)
• the conditions in which they have developed (environmental causes) e.g. colour of flowers depend on pH of the soil
  language in humans (variation caused by environment)
• a combination of genes and the environment. e.g. height (some people have alleles which make them likely to grow taller) However their diet must also include enough calcium for their bones to fully develop. In this case, their final height is a combination of genetics and the environment

Question 3

Causes of genetic variation

Answer 3

All of this genetic variation is due to mutations

Question 4

Mutations

Answer 4

Mutations are random changes to DNA

Question 5

Features of mutatitions

Answer 5

Mutations take place all the time
Most mutations have no effect at all on the phenotype

Some mutations influence the phenotype E.g. alleles for tallness may lead to tallness if a persons diet is suitable

A small number of mutations determine the phenotype e.g. eye colour

Very rarely can mutation lead to a new phenotype
Sometimes the new phenotype can be beneficial if the environment changes
Leads to a rapid change in the species

Question 6

What is evolution

Answer 6

a change in the
inherited characteristics of a population over time through a process of
natural selection which may result in the formation of a new species

Question 7

What is the theory of evolution by natural selection

Answer 7

The theory of evolution by natural selection states that all species of
living things have evolved from simple life forms that first developed
more than three billion years ago.

Question 8

Explain how evolution takes place through natural selection

Answer 8

Every rabbit will have a slightly different combination of alleles that it inherited from its parents
Some rabbits will have alleles for thicker fur
If the environment changes, and becomes a lot colder
The rabbits which have inherited alleles for thicker fur have an advantage and are more likely to survive the colder temperatures than rabbits with thinner fur
So because the rabbits with thicker fur can survive the cold, they are more likely to go on to reproduce
Their offspring could inherit the (beneficial alleles) alleles for thicker fur and these offspring are also more likely to survive the cold are reproduce
This is called natural selections

Over many generations, the alleles for thicker fur will become more common among the population of rabbits
And overall, the rabbit population will tend to have thicker fur than before

Question 9

What is speciation

Answer 9

If two populations of one species become so different in phenotype
that they can no longer interbreed to produce fertile offspring they have
formed two new species.

Question 10

Examples of selective breeding

Answer 10

The characteristic can be chosen for usefulness or appearance:

Food crops such as wheat have been selectively bred to be resistant to disease
* Animals such as cows have been selectively bred to produce more meat or milk.
* Domestic dogs have been selectively bred to have a gentle nature.

Certain plants have been selectively bred to produce large or unusual flowers

Question 11

Describe how selective breeding is carried out

Answer 11

Selective breeding involves choosing parents with the desired characteristic from a mixed population.

They are bred together.

(sexual reproduction produces variation in the offspring)

From the offspring those with the desired characteristic are bred together.

This continues over many generations and the desirable trait gets stronger and stronger. Eventually all the offspring show the desired characteristic

Question 12

Disadvantages of selective breeding

Answer 12

Selective breeding can lead to ‘inbreeding’.
Inbreeding can cause some breeds are
particularly prone to disease or inherited defects

Question 13

What is selective breeding

Answer 13

Selective breeding (artificial selection) is the process by which humans
breed plants and animals for particular genetic characteristics

Question 14

What is genetic engineering

Answer 14

Genetic engineering is a process
which involves modifying the genome of an organism by introducing a
gene from another organism to give a desired characteristic

Question 15

Examples/uses of genetic engineering

Answer 15

In genetic engineering, genes from the chromosomes of humans and
other organisms can be ‘cut out’ and transferred to cells of other
organisms.

Plant crops have been genetically engineered to be resistant to diseases (or insect attack) or to produce bigger or better fruits. (We have transferred genes into plants to produce Genetically modified crops - GM crops) - GM crops produce a greater yield than normal crops

Bacterial cells have been genetically engineered to produce useful substances such as human insulin to treat diabetes.

Question 16

What are GM crops

Answer 16

Crops that have had their genes modified in this way are called
genetically modified (GM) crops

Question 17

Advantages of GM crops

Answer 17

GM crops include ones that are
resistant to insect attack or to herbicides. GM crops generally show
increased yields.
produce bigger or better fruits

resistant to herbicides - this means that farmers can spray their fields to kill weeds without harming the GM crop

Question 18

concerns of GM crops

Answer 18

the effect on populations of wild
flowers and insects. (if they are safe/could they be harmful to insects or wild flowers)
Some people feel the effects of eating GM crops on human health have not been fully explored.

Question 19

How genetic modification crops are being used in medicine

Answer 19

Modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders
This is called gene therapy

Question 20

Describe genetic engineering

Answer 20

Identify the gene we want to transfer (e.g. a human gene, gene from an animal or gene from a plant)
A useful gene is isolated (cut) from one organisms genome using enzymes and is inserted into a vector
The vector is usually a virus or a bacterial plasmid, depending on the type of organism that the gene is being transferred to (useful for transferring DNA from one organism to another)
(CALLED VECTORS BECAUSE THEY TRANSFER THE DNA FROM ONE ORGANISM TO ANOTHER)
When the vector is introduced to the target organism, the desired gene is inserted/transferred into its cells

Question 21

Explain why the gene is always transferred at an early stage in the organisms development
e.g. if we were transferring a gene into an animal, we would do this at the early embryo stage

Answer 21

This is to make sure that all of the cells receive the transferred gene
This way, the organism develops with the desired characteristics

genes are transferred to the cells of animals, plants or
microorganisms at an early stage in their development so that they
develop with desired characteristics.

Question 22

Advantage of cloning plants

Answer 22

Because the clone is genetically identical to the original plant, we know exactly what the clones characteristics will be (e.g. the colour of the flower)

(if seeds were used - which are produced by asexual reproduction - then all of the offspring would be different

Question 23

How to clone a plant

Answer 23

Take cuttings

Question 24

Describe how cuttings (to clone a plant work)

Answer 24

A small piece of the plant is removed and the end is dipped in rooting powder
Rooting powder contains plant hormones - this encourages the plant to develop roots

By taking cuttings we produce a genetically identical clone of the starter plant

Question 25

When are cuttings good

Answer 25

Taking cuttings works really well if we just want a few clones from the plant

Question 26

What do we use if we need hundreds of clones from a plant

Answer 26

USE TISSUE CULTURE

Question 27

Describe tissue culture

Answer 27

Take the plant we want to clone and divide the plant into hundreds of tiny pieces
Each of these pieces contains a small number of cells
These small groups of cells are then incubated with plant hormones
The plant hormones stimulate the plant to grow and develop into fully-grown clones
The conditions that we use for tissue culture must be sterile. This is because we dont want to introduce any microorganisms such as bacteria or fungi

Question 28

Advantages/uses of tissue culture/importance

Answer 28

This is important for preserving rare plant species
or commercially in nurseries (allows growers to produce thousands of genetically identical plants quickly and cheaply)

Question 29

Types of animal cloning

Answer 29

Embryo transplants
Adult cell cloning

Question 30

Describe cloning by embryo transplants

Answer 30

Take a sperm and egg cell from the animal with the desired characteristics
Fertilisation produces a fertilised egg
Allow the fertilised egg to develop into an early stage embryo
it is very important that the cells in this embryo must not have started to specialise
Use a glass rod to split this embryo into two
Transfer the two embryos into host mothers
The embryos will then grow and develop
When these animals are born, we will get two identical offspring (clones)

Question 31

Problem with embryo transplants

Answer 31

Because we start with sperm and an egg, we cannot be certain that the offspring will have the characteristics that we want.

Question 32

Problem with embryo transplants: Because we start with sperm and an egg, we cannot be certain that the offspring will have the characteristics that we want.

How can we overcome this problem

Answer 32

We can overcome this problem by using adult-cell cloning

Question 33

Describe adult cell cloning

Answer 33

The nucleus is removed from an unfertilised egg cell. - contains no genetic material at all
* The nucleus from an adult body cell, (this nucleus contains the genetic information from the animal that we are cloning) such as a skin cell - (from same species), is inserted into the egg cell (egg cell contains only genetic information from the animal that we are cloning)
* An electric shock stimulates the egg cell to divide to form an embryo.
* These embryo cells contain the same genetic information as the adult skin cell.
* When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.

The host mother then gives birth to the clone.

Question 34

Benefits of adult cell cloning

Answer 34

With adult cell cloning, we are cloning from an adult
This means that we know the characteristics that the clone will have

Question 35

Key facts about adult cell cloning

Answer 35

The clone looks nothing like the host mother
This is because the clone contains none of their genetic material