Lecture 3

Question 1

What are the 4 mechanisms of cloning?

Answer 1

Natural (asexual)
Embryo splitting
Reprogramming somatic cells
Nuclear transfer

Question 2

How are twins formed in humans?

Answer 2

Blastomeres in a 2 cell embryo separate naturally at an early stage with each embryo having their own placenta and nutrients. If it happens at a later stage, after the embryo has planted this will cause competition for nutrients.

Question 3

How does reprogramming somatic cells form clones?

Answer 3

By reversing cell differentiation (usually in plants) E.g. a carrot root cell can be used to make a clone of the original.

Question 4

Why is somatic cell nuclear transfer controversial?

Answer 4

The technique is manipulative and invasive, and there are ethical and technical problems.

Question 5

How is it possible?

Answer 5

Nucleus of every somatic cell contains the complete genome and a fertilised egg is totipotent. Both of these are used to form the clone.

Question 6

What is the mechanism?

Answer 6

DNA from one cell is combined with an enucleated fertilised egg.

Question 7

What was the first mammal cloned by SCNT and who cloned it?

Answer 7

Megan & Morag by Wilmut and Campbell in 1995.

Question 8

How was this carried out?

Answer 8

A sheep embryo was deprived of growth factor which arrested it’s development. This DNA is transferred to a cytoplast (enucleated egg) and then into a surrogate.

Question 9

What is the issue with this method of cloning?

Answer 9

Because they were cloned from embryonic cells, they may still have had some totipotency.

Question 10

Why was Dolly different?

Answer 10

It was the first mammal cloned from differentiated adult cells.

Question 11

How was Dolly cloned?

Answer 11

Mammary gland cells were deprived of growth factor to arrest development. These cells were fused with cytoplasts and stimulated to grow to an early embryo stage before being transplanted into a surrogate.

Question 12

Why was Dolly (a Dorset Sheep) put into a Scottish Black Faced surrogate.

Answer 12

Because of large fetus syndrome.

Question 13

What was the first transgenic mammal?

Answer 13

Polly.

Question 14

What was Wilmutt and Campbell’s goal?

Answer 14

To create a transgenic flock of sheep that could produce therapeutically useful proteins in their milk.

Question 15

What is the issue with this?

Answer 15

It is time consuming and clones that are male are not useful.
Easier to genetically modify one sheep and clone it rather than breed them.

Question 16

How are transgenic clones made?

Answer 16

Genetically modified embryo cells are transferred into cytoplasts.

Question 17

What did Polly’s milk contain?

Answer 17

Human factor 4, a blood clotting agent used to treat haemophillia.

Question 18

What are some potential uses of cloning?

Answer 18

Developmental research (clones as controls).
To conserve rare and endangered animals.
Cloning elite livestock.
Disease resistance farming.
Assisted reproductive techniques.
Therapeutic cloning to replace body parts.
Pharming (Useful drugs in milk).
Xenotransplantation (use of animal organs in humans).

Question 19

What are the issues of cloning for conservation?

Answer 19

Who decides what animals should be cloned? Also the original problem of habitat loss isn’t addressed.

Question 20

How is cloning currently used?

Answer 20

Mice, pigs, cows, goats etc have been cloned and goats and sheep have been genetically engineered to produce useful proteins.

Question 21

How do clones differ from the original?

Answer 21

Because they are DNA clones and cytoplasm plays a big role in development (which is different in the clones). Also clones have their own mutations and environment is important.

Question 22

Why are telomeres a problem in clones?

Answer 22

Clones have the telomeres of their hosts DNA so they are shorter than non-clones. This could be remedied with enzymes.

Question 23

What is the success rate?

Answer 23

1/277 transnucleated clones in Dolly trials.

Question 24

What are other issues of cloning?

Answer 24

Lack of genetic variation could cause disease vulnerability. Could be psychological problems for human clones.

Question 25

What are stem cells?

Answer 25

Undifferentiated cells capable of extensive proliferation.

Question 26

What do stem cells produce?

Answer 26

Active stem cells and differentiated progeny cells.

Question 27

How are stem cells differentiated?

Answer 27

By cytoplasmic signals E.g. brain stem cells form nerve cells.

Question 28

How else can stem cells be differentiated?

Answer 28

Using differentiation factors. Helps overcome rejection of transplanted organs as they are a clone of the patient.

Question 29

What is an example of a signal that causes stem cell differentiation?

Answer 29

Stem cells given vitamin A derivatives form stem cells.

Question 30

Problems of using stem cells?

Answer 30

The creation and destruction of human embryos to gain stem cells.

Question 31

Solution to this?

Answer 31

Using stem cells from bone marrow and umbilical cords.

Question 32

How can stem cells be used to treat Parkinson’s.

Answer 32

Embryonic stem cells can be used to produce dopamine to replace dopamine that is lacking because of the loss of dopamine producing cells that die off.