Genetic variation and its control

Question 1

What does the nucleus of a cell contain?

What do these structures carry?

Answer 1

The nucleus of a cell contains thread-like structures called chromosomes which carry genes.

Question 2

What is different about the chromosomes in the nuclei of sex cells?
What does this mean about the genes in the nuclei?

Answer 2

There is only a single set of chromosomes in the nuclei of sex cells, which means they also contain only one set of genes.

Question 3

What do different genes control?

Answer 3

Different genes control the development of different characteristics.

Question 4

In most body cells how are the chromosomes arranged?

Where did the chromosomes come from?

Answer 4

In most body cells the chromosomes are arranged in pairs, one set came form the female gamete and one set came from the female gamete.

Question 5

What is asexual reproduction?

What are identical copies produced by asexual reproduction called?

Answer 5

Asexual reproduction dose not involve the fusion of gametes, all of the genetic information comes from one parent. All the offspring are genetically identical to the parent, so there is little variety.
Clones.

Question 6

What is sexual reproduction?

What are the sex cells in animals?

What can be said about offspring produced by sexual reproduction?

Answer 6

Sexual reproduction involves the fusion of gametes, there is a mixing of genetic information, so the gametes show variety.
The sex cells in animals are egg and sperm cells.
Offspring produced by sexual reproduction are similar to both parents, but cannot be identical, this is because they have a random combination of two sets of genes.

Question 7

Why is variation important for survival?

Answer 7

Variation is important for survival as some characteristics may give offspring a better chance of surviving difficult conditions.

Question 8

What may differences in the characteristics of individuals of the same species be due to? (3)

Answer 8

1) Differences in the genes they have inherited.
2) The conditions in which they have developed.
3) A combination of both these genetic and environmental causes.

Question 9

What is the most important factor in controlling the appearance of an individual?

Answer 9

Genes

Question 10

What environmental factors may affect plants? (3)

Answer 10

1) Lack of light
2) Lack of nutrients
3) Lack of space to grow

Question 11

How may human development be affected during pregnancy?

Answer 11

If the mother smokes or drinks a lot, the baby may have a small birth weight.

Question 12

Once animals are born what environmental factor may alter their characteristics?

Answer 12

Too much or too little food.

Question 13

What is cloning used for mainly?

Answer 13

To produce new individuals that are useful in farming and agriculture.

Question 14

What is the cheapest and most effective way of cloning plants?

Answer 14

Taking cuttings and growing them.

Question 15

What is tissue culture?
What is the drawback of this process?
What is it used for?

Answer 15

Tissue culture involves taking small groups of cells from part of a plant and growing them under special conditions, it is very expensive.
Tissue culture can be used to reproduce large numbers of a rare or top quality plant.

Question 16

For what are embryo transplants used?

Describe the process of an embryo transplant. (2)

Answer 16

Embryo transplants are used to clone animals.

1) In this process an embryo with unspecialised cells is split into smaller groups of cells.
2) Each group of genetically identical cells is transplanted and allowed to develop in a host mother.

Question 17

What can be done to animals or plants to produce useful substances before they are cloned?

Answer 17

They can be genetically modified.

Question 18

Describe the process of adult cell cloning. (5)

What was the first animal to be produced by adult cell cloning and when was this done?

Answer 18

1) The nucleus is removed from an unfertilised egg cell.
2) The nucleus from a skin cell of the animal to be cloned is removed and placed inside the ‘empty’ egg shell.
3) The new cell is given an electric shock to cause it to start to divide into a ball of cells called an embryo.
4) The embryo is genetically identical to the skin cell, once the embryo has developed into a ball of cells it is inserted into the womb of a host mother.
5) If all goes well the embryo will develop naturally inside the host mother.

Dolly the sheep was produced by adult cell cloning in 1997.

Question 19

Outline three advantages and three disadvantages of adult cell cloning.

Answer 19

Advantages:
1) Development of cloned animals which have been genetically engineered to produce valuable proteins in their milk, which can be used in medicine.
2) Cloning can save animals from extinction.
3) May be used to make copies of the best animals.
Disadvantages:
1) Concerns about the ethics of cloning
2) Cloning limits the variation in a population, this can be a problem for natural selection if the environment changes.
3) Concerns about using the technique to clone humans in the future.

Question 20

What is genetic engineering?

When is this done?

Answer 20

Genetic engineering involves changing the make-up of an organism. Genes can be transferred to an organism at the early stage of its development.

Question 21

How is genetic engineering carried out? (2)

Answer 21

1) A gene is ‘cut out’ of the chromosome of an organism using an enzyme.
2) The gene is then placed in the chromosome of another organism.

Question 22

Give two main ways in which genetic engineering may be carried out?

Answer 22

1) The genes may be placed in an organism of the same species to give it a desired characteristic.
2) Sometimes genes are placed in a different species, such as bacterium. For example, the gene to produce insulin in humans can be placed in bacteria, the the bacteria can produce large quantities of insulin to treat diabetes.

Question 23

Give one way in which genetic engineering may be used?
What are crops that have been genetically engineered called?
Why may crops be genetically engineered?

Answer 23

To transfer new genes to crop plants.
Genetically Modified (GM) crops.
GM crops may be insect or herbicide-resitant and usually have increased yields.

Question 24

Outline three advantages and five disadvantages of genetic engineering.

Answer 24

Advantages:
1) If a person has a faulty gene, they may have a genetic disorder, if the correct gene can be transferred to the person they could be cured.
2) Several medical drugs such as insulin and antibodies have been produced by genetic engineering.
3) GM include one which are resistant to herbicides or insects and have increased yields.
Disadvantages:
1) Farmers have to buy new GM seed every year because the crops are infertile.
2) Some people are worried about accidentally introducing genes into wild flower populations.
3) Insects which are not pests may be affected by GM crops.
4) Many people worry about the affect of eating GM crops on human health.
5) Many people think genetic engineering is unethical.