AQA GCSE Cloning(Biology) - Science Worksheets

AQA GCSE Cloning (Biology)

Cloning

Cloning is the production of genetically identical copies of a cell or organism.

It is a type of asexual reproduction, meaning no fertilisation is involved.

Plant Cloning

There are two ways that we can clone plants:

1.Cuttings

2. Tissue culture

Cuttings

Cuttings are a simple method where a piece of a plant (e.g. stem) is cut, dipped into rooting powder (auxin), then planted in compost to grow a new identical plant.

Cuttings can be carried out by anyone.

In the diagram below:

Stage 1 a section of plant is removed with a knife e.g. stem or leaf.

Stage 2 The base of the stem of this piece of plant tissue is placed into rooting powder (auxin) to develop roots

Stage 3 The piece of plant tissue previously dipped into rooting powder is now planted into compost, roots will grow and a new plant will form.

Tissue Culture

Tissue culture involves taking a small group of cells from a plant and growing them in sterile conditions to produce many identical plants.

Stage 1: A small piece of plant tissue is taken from the plant using a scalpel. These pieces of tissue are known as explant, because they came from the plant.

Stage 2:The pieces of plant tissue are placed in dilute bleach to sterilse them, then grown on sterile agar containing nutrients and hormones which results in a large mass of plant tissue called a callus being formed.

Stage 3: Different ratios of plant hormones are used to make the callus cells differentiate into roots and shoots, forming plantlets

Stage 4: The plantlets are potted into compost to grow into plants.

Animal Cloning Methods

There are two methods to clone animals

1.Embryo Transplants

2.Adult cell cloning

Embryo Transplants

In embryo transfer, female animals are given hormones (such as FSH) by injection to stimulate the ovaries to release multiple eggs (superovulation).

These eggs can then be fertilised and the embryos collected.

1. FSH is given to the cow by injection to stimulate the ovaries to release multiple eggs.

2.Fertilisation occurs where sperm fertilise the eggs

3. Embryos form inside the uterus of the cow

4. Embryos collected from mother and transferred to petri dish in lab

Cells from an early embryo are split before they specialise. Each cell can develop into a separate embryo.

These split embryos are implanted into host mothers.

Stage 1 the embryo is split

Stage 2 the cells divide by mitosis to reform new embryos

Stage 3 the embryos are implanted into a surrogate mother

Stage 4 the calves are born, these are genetically identical to each other, so they are clones of each other.

Adult Cell Cloning

Adult cell cloning was used to produce Dolly the sheep!

1.An egg cell is taken from a sheep

2. The nucleus is removed from the egg cell, leaving an empty egg cell which is retained and the nucleus is discarded

3. A body cell is taken from another sheep, in this case a brown sheep

4. The nucleus is extracted from this body cell and retained. The empty body cell is discarded.

5. The empty egg cell is fused with the nucleus to form a fertilised egg cell. This fertilised egg cell is given an electric shock to make it divide by mitosis to form an embryo

6. The embryo is implated into a surrogate mother sheep

7. A lamb is born that is genetically identical to the sheep which provided the nucleus. In this case the brown sheep.

Benefits of Cloning

Agriculture

If an animal has been genetically engineered or selectively bred to have favourable characteristics e.g. high milk yield. Then this animal can be cloned to produce many of them with this characteristic.

Faster production of livestock

Consistent quality of crops as you always know the characteistic that you will have

Organisms that are endangered can be cloned to prevent extinction

Medicine

Stem cells can be cloned to produce more stem cells for treating diseases and for research

Could help replace damaged tissues/organs, by cloning cells.

Risks of Cloning

Reduced genetic variation as all the individuals are genetically identical. This means the populations more vulnerable to disease. An example is banana trees that are clones, these are currently being affected by a fungus.

Cloned animals may have more health problems than a normal animal

Expensive and low success rate. Dolly the sheep needed about 277 attempts for cloning to be successful!

Ethical Issues

Some people object to cloning because:

It may cause suffering to animals

It is seen as “unnatural”

Concerns about cloning humans

Practice Questions

1.What is meant by the term clone?

2.Outline the process of adult cell cloning.

3.Why are hormones given to female animals in embryo transfer?