Cloning

Question 1

what do organisms from when they divide asexually?

Answer 1

clones

Question 2

what happens in mitosis?

Answer 2

Two identical copies of the DNA are created in mitosis, each copy is then are separated into one of two genetically identical nuclei

Question 3

define clones

Answer 3

Organisms or cells that are genetically identica

Question 4

what are some examples of organisms that are capable of asexual reproduction to form clones

Answer 4

bacteria and plants

Question 5

what are some advantages of natural cloning?

Answer 5

Reproduction can occur without needing another organism of the same species for sexual reproduction. This is more convenient as you can produce many offspring in a smaller time frame

It allows an organism to take advantage of favourable environmental conditions; if the parents are suited to the environmental conditions, their offspring will be too

Question 6

what are some disadvantages of natural cloning?

Answer 6

There is less genetic diversity in the population, with only mutations giving rise variation. Selection is not possible

If environmental conditions alter, the entire population will be affected as they will be less able to adapt

As cloning produces many offspring, this could lead to eventual overcrowding within the population

Question 7

what is meant by totipotent?

Answer 7

able to differentiate into any cell

Question 8

what is the benefit of many plant cells being totipotent?

Answer 8

This allows adult plants to form natural clones through a process known as vegetative propagation.

The plants reproduce through the vegetative parts of a plant (e.g. roots and leaves)rather than the reproductive structures (e.g. petals).

Question 9

define vegetative propagation

Answer 9

Asexual reproduction from the vegetative parts of a plant rather than through specialised sexual reproductive structures.

Question 10

what is the benefit of the vegetative parts of the plant which are over-wintering (perennating organs)?

Answer 10

they allow plants to survive through the winter

Question 11

what are the 2 types of over-wintering organs that are used for vegetative propagation?

Answer 11

-bulbs
- tubers

Question 12

describe the structure and function of bulbs

Answer 12

Bulbs consist of an underground stem from which fleshy leaf bases sprout. This leaf base contains food reserves that allow the plant to survive adverse environmental conditions (e.g. winter). The bulb also contains apical buds, which develop into new shoots and eventually new plants during the growing season. The new individual plants that grow are natural clones of the old plant. Corms are similar to bulbs but are solid rather than fleshy. They are underground stems with scaly leaves and buds which also remain in the ground during winter.

Question 13

give some examples of bulbs

Answer 13

daffodils and onions

Question 14

describe the structure of tubers

Answer 14

Tubers consist of underground stems which become large, underground structures as they become swollen with stored food. Tubers also form buds that often can go on to form shoots, which can then develop into cloned plants

Question 15

give some examples of tubers

Answer 15

potatoes and sweet potatoes

Question 16

what is meant by horizontal stems?

Answer 16

Some plants are able to develop stems that grow horizontally away from the parent plant and are able to form roots of their own.

Question 17

what are the 2 kinds of horizontal stems?

Answer 17

Runners/stolons — when the horizontal stems run above the ground
Rhizomes — when the horizontal stems go underground

Question 18

what is meant by ‘suckers’ and what do they do?

Answer 18

When a new stem grows from the roots of a plant, they are called suckers.
They can either grow near the base of the original stem or further away from it

Question 19

what happens to the original stem of suckers?

Answer 19

The original horizontal stem often dies leaving the new stem as a separate individual

Question 20

explain how vegetative propagation happens in leaves

Answer 20

vegetative propagation can also occur in leaves.

Smaller plants grow along the leaf margin and eventually drop from the leaf on to the ground.

These can then go on to form their own roots and grow, being a clone of the parent plant

Question 21

what are plant cutting used to do?

Answer 21

Cuttings exploit vegetative propagation in order to create clones of a plant. This technique can be used to produce large numbers of plants very quickly

Question 22

describe the 2 step method used to clone plants using plant cuttings

Answer 22

Cuttings are primarily made from stems.

The stem is cut between two leaf joints (nodes) and the cut end is replanted into the soil

Parts of tissues in the stem develop into new roots — this can be promoted by submerging the base of the cut stem in rooting hormone

Question 23

where in plants can cuttings be taken from?

Answer 23

stem
roots
leaves

Question 24

if a cutting is taken from the roots, what happens?

Answer 24

If taken from the roots, the cut root is buried just below the soil surface and goes on to develop shoots and eventually new plants

Question 25

if a cutting is taken from the leaf, what happens?

Answer 25

If taken from a leaf, the cut leaf is placed on moist soil. It then develops new shoots and roots

Question 26

why were methods of artificial cloning developed when we have natural cloning methods?

Answer 26

natural cloning can be very time-consuming and only a limited number of cuttings can be taken from one plant.

Therefore, methods of artificial cloning have been developed so that hundreds of plants can be rapidly cloned.

Question 27

name some methods of artificial cloning

Answer 27

micropropagation and tissue culture

Question 28

define micropropagation

Answer 28

The process of growing large numbers of cloned plants from meristem tissue taken from a sample plant

Question 29

what are some factors that make micropropagation possibe?

Answer 29

Micropropagation is possible because meristem plant cells are totipotent.

Micropropagation also requires the use of plant tissue cultures.

In these cultures, cells, tissues, and organs are grown from a small sample of cells or tissue.

Question 30

define tissue culture

Answer 30

The growth of tissues or cells in an artificial medium taken from tissues of a sample plant.

Question 31

what are the conditions of the medium that tissues are cultured on to allow maximal growth?

Answer 31

It contains nutrients necessary for growth such as glucose and phosphates

The medium also usually contains a mixture of plant hormones (e.g. auxin and cytokinin) essential for the promotion of cell differentiation

The medium must also be sterile to prevent the growth of unwanted bacteria and/or fungi – meristem tissue is usually used as it is typically virus-free

Question 32

what is the 6 step method used to carry out micropropagation?

Answer 32

1–Small samples of plant meristem tissue, called explants, are dissected from the plant

The explants are sterilised using either bleach or ethanol to kill any unwanted microorganisms which often compete with plant cells, limiting their growth

The explants are then placed on a sterile culture medium which contains the necessary nutrients and plant hormones. This helps stimulate growth via mitosis and forms a mass of undifferentiated cells called a callus

The main callus that was formed is then divided into a large number of smaller clumps of cells. These are then moved to another culture medium that stimulates the development of roots
Once the roots have developed, the clump of cells is then transferred to a different culture medium that stimulates the development of shoots. This results in the formation of tiny plants (plantlets)

The plantlets are then potted in soil to grow into larger plants. These plants are all genetically identical clones of the original sample plant

Question 33

what are some advantages of using artificial cloning in agriculture and horticulture (6)?

Answer 33

New plants can be grown quicker than growing plants from seeds,so it is more time efficient and produces more plants in the same time-frame

Desirable traits can be retained more reliably than traits derived from sexual reproduction

Allows for the development of plants that are naturally hard to grow from seeds such as orchids
The method of micropropagation ensures that the developing plant is free from viruses so is more likely to grow

Provides a means of increasing the numbers of rare or endangered plants

The new plants’ phenotypes are uniform, making them easier to harvest and grow

Question 34

what are some disadvantages of using artificial cloning in agriculture and horticulture (3)?

Answer 34

Artificial cloning produces a monoculture of genetically identical plants with no variation. This makes it more susceptible to diseases or pests as they will not be able to acclimatise to changes in environmental conditions
Micropropagation is expensive and labour intensive
Large numbers of plants can also be lost if the culture is contaminated with bacteria or fungi

Question 35

why is using natural cloning advantageous in animals?

Answer 35

as it can produce a large number of animals possessing the desirable trait.

Question 36

why cells are used for artificial cloning of plants?

Answer 36

-with plants, artificial cloning uses totipotent cells (able to differentiate into every cell type),therefore only early embryonic stem cells are used (the only type of cell in humans that is totipotent).

Question 37

what are 2 methods currently used to produce artificial clones?

Answer 37

-Embryo splitting
- Somatic cell nuclear transfer (SCNT)

Question 38

explain embryo splitting

Answer 38

Artificial embryonic twinning normally splits the early embryos manually into two, forming two independent, genetically identical embryos.

However, artificial embryo splitting splits the same early embryo into many embryos,all of which are genetically identical.

This gives rise to clones which are genetically identical to one another, but not the parent

Question 39

define embryo twinning

Answer 39

The process of splitting an early embryo in half to create two genetically identical embryos

Question 40

describe the 5 step process in which artificial embryo splitting occurs

Answer 40

1-A female animal with desirable traits is treated with hormones resulting in the release of many eggs (ova)

The eggs are then either:
Fertilised inside the female animal and once the early embryos are formed, they are flushed out
Removed from the female animal and fertilised in the lab by in vitro fertilisation (IVF)
Whilst the embryonic cells are still totipotent, they are manually split to produce many smaller embryos (embryonic splitting)
The split embryos are then left to carry on dividing in vitro for a few days to ensure development proceeds correctly
If divided correctly, each embryo is then placed into the uterus of a surrogate mother. The embryos then develop into foetuses and are born normally. Ultimately many genetically identical cloned animals are produced

Question 41

which organisms are cloned using somatic cell nuclear transfer (SCNT)?

Answer 41

-adult animals

Question 42

what does SCNT stand for?

Answer 42

somatic cell nuclear transfer

Question 43

what were 3 things that were required to cone Dolly the sheep?

Answer 43

=This required three animals of the same species to achieve:
* A female egg donor
* A female surrogate mother
* The animal to be cloned

Question 44

define somatic cell nuclear transfer (SCNT)

Answer 44

Method of cloning that is achieved by transferring the nucleus from a somatic (body) cell of an adult animal into an egg cell.

Question 45

what is the 6 steps that artificial embryonic splitting occurs in?

Answer 45

1- The egg cell (ovum) is harvested from a female animal and the nucleus is removed in a process known as enucleation

2-. A somatic (body) cell from the adult animal to be cloned is then isolated

The somatic cell is then either:
Enucleated (i.e. nucleus is removed), and transferred into the enucleated egg cell
Joined together with the enucleated egg cell using electrofusion
Both procedures require an electric shock which stimulates the division of the reconstructed egg cell
The cell then undergoes many rounds of mitosis to form an embryo which is subsequently implanted into the uterus of a surrogate mother
The embryo develops into a foetus and a clone of the original animal is born

Question 46

what is the difference between embryo splitting and SCNT?

Answer 46

embryo splitting, the clones are genetically identical to one another and not the parent; whilst in SCNT the cloned animal is genetically identical to the parent.

Question 47

what is non- reproductive cloning?

Answer 47

Non-reproductive cloning is the production of cloned cells and tissues for use outside of reproduction.

Question 48

what are cloned cells used for + its benefit?

Answer 48

for therapeutic reasons – specifically for the growth of replacement organs/tissues.

This is advantageous,as the cells will be genetically identical to the patient’s own cells,and there will be no issue with rejection.

Question 49

what can cloned tissues/cells be used for?

Answer 49

for medicinal drug testing
cloned embryos can be used to determine the impact genes can have on development.

They are also useful for scientific research looking into the action of genes that control development and differentiation

Question 50

what are some advantages associated with artificial cloning? (6)

Answer 50

Splitting embryos allows for large numbers of animals to be produced from parents with desirable genes

Clones as embryos can be frozen to ensure the desirable genes were passed on before allowing them to develop

SCNT allows for genetically identical copies of high-value organisms such as GM animals to be developed

SCNT can also be used to clone rare or endangered species to increase their numbers in a population
Can test medicinal drugs on cloned cells/tissues, avoiding animal testing (which has ethical issues of its own)

It can be used to form tissues and cells for repairing damage caused by disease or accidents. These tissues and cells are genetically identical to the patient so therefore are not rejected

Question 51

what are some disadvantages associated with artificial cloning? (4)

Answer 51

Reduces genetic variation so the clones are more prone to diseases and pests

SCNT brings up ethical issues regarding the use of multiple eggs in which only one successful clone is produced

Many embryos formed from SCNT fail to develop normally,resulting in miscarriages or malformed offspring

Clones that have been brought to term may have numerous health problems and often have shorter life spans, e.g. Dolly the sheep