Chapter 1 - Cloning in Plants and Animals Flashcards
What are totipotent stem cells?
They are capable of differentiating into any type of adult cell found in the organism.
Outline the differences between reproductive and non reproductive cloning.
Reproductive cloning - produces offspring that is genetically identical to either the mother (nuclear transfer) or the other offspring (splitting embryos)
Non reproductive cloning - use of stem cells to generate replacement cells, tissues or organs that can then be used to treat diseases/conditions.
What are the two methods of artificially cloning animals?
Splitting embryos and nuclear transfer.
Describe the process of “splitting embryos”
- eggs collected from high value female + sperm from HV male
- they are fertilised in vitro and this is allowed to grow in vitro to a 16-cell embryo
- the embryo is split into several segments, which are then implanted into surrogate mothers.
- each calf is a clone.
Describe the process of “nuclear transfer”
- differentiated cell from adult is taken (eg mammary cell from udder)
- nucleus is placed in an enucleated egg cell from a different adult
- electrofusion is used to reconstruct cell
- embryo is implanted in surrogate mother’s uterus
- clone born
Discuss the advantages and disadvantages of cloning animals
ADVANTAGES
- high value animals, eg cows with high milk yield, can be cloned in large numbers
- rare animals can be cloned to preserve species
- genetically modified animals (eg sheep that produce pharmaceutical chemicals in milk) can be quickly reproduced.
DISADVANTAGES
- lack of animal welfare
- lack of diversity in a species makes it unlikely to be able to cope with/adapt to changes in environment
- unclear of long term risks to health
What is therapeutic cloning? What are the advantages and risks?
Therapeutic cloning is using clones cells to generate tissues/organs to replace those damaged by diseases.
ADVANTAGES
- genetically identical to own cells/not be “rejected”
- end to current problem of waiting for a donor
- totipotent
RISKS
- ethical issues
- scientific concerns about long term behaviour of cloned cells
Describe the production of natural clones in plants using the example of vegetative propagation in elm trees
- asexual reproduction takes place naturally in the elm tree. They are adapted to reproduce asexually following damage to the parent plant.
- new growth in the form of basal sprouts appear after the destruction of the parent plant
- they grow from meristem tissue in the trunk, where least damage is likely to have occurred.
What are disadvantages to the vegetative propagation in elm trees?
- lack of genetic variety means that if a new disease enters the environment, all new trees are as susceptible to the disease as the parent plant.
- eg dutch elm disease - once new trees got to about 10cm in diameter, they become infected and die.
Describe 2 methods of artificial cloning for plants
TAKING CUTTINGS
- stem is cut between lead joints
- stem is treated with plant hormones to encourage growth + is then planted
GRAFTING
- shoot section of woody plant is cut
- joined to already growing root and stem (known as a “rootstock”)
- graft grows + is genetically identical to parent plant but the rootstock is genetically different
Describe a method of artificial propagation for large scale cloning
-cuttings and grafts cannot produce huge numbers of cloned plants very easily
MICROPROPAGATION BY TISSUE CULTURE
- small piece of tissue is taken from the shoot called an explant, sterilised using bleach
- place explant on agar which contains glucose, amino acids, nitrates and phosphates.
- Forms a callus (mass of undifferentiated cells) by treating the explant with high auxin and cytokinin concentrations
- subdivide the callus and induce roots and shoots by changing the plant hormone ratio
- transfer to a greenhouse to be acclimatized before planted outside
