6.2.1 - (b-d)

Question 1

Give exmaples of natural cloning in animal species

Answer 1

In invertebrates

• They can reproduce asexually by budding or parthenogenesis (reproduction from an ovum without fertilisation in invertebrates)

In vertebrates

• Main form of vertebrate cloning is forming monozygotic twins (identical twins)
• The early embryo splits forming 2 embryos – known as embryo splitting

Question 2

What is micropropagation and tissue culturing?

Answer 2

Micropropagation: Process of making large numbers of genetically identical offspring from a single parent plant using tissue culturing

cloning of cells from a small group of genetically identical cells to from a mass of similar cells)

Question 3

When is micropropagation using tissue culture used in plants?

Answer 3

Used when the desirable plant…

• Doesn’t readily produce seeds
• Does not respond well to natural cloning
• Is rare
• Is a GMO or has been selectively bred
• Required to be pathogen-free

Question 4

Why must micropropagation be done under aseptic conditions?

Answer 4

Micropropagation using tissue culture must be done under aseptic conditions, the conditions needed for the explant to grow include: moisture, warmth, nutrients. Which are ideal for microorganisms that will grow quickly and destroy the rare plants

Question 5

What are the principles of micropropagation using tissue culture?

Answer 5

1. Take a small tissue sample from the desired plant to clone
   
   1. Meristem tissue from shoot tips and axial buds is dissected in sterile conditions to avoid fungal/bacterial contamination and the tissue is virus-free
2. Sterilise the sample by immersing in a sterilising agent (e.g. bleach, ethanol, sodium dichloroiosocyanurate)
   
   1. Explant: The tissue removed from the plant that can be cultured to grow a new plant
3. Place the explant in a sterile culture medium with plant hormones and nutrients (auxins, cytokinins) stimulating mitosis – the cell proliferation stimulates a mass of cloned cells called a callus which is totipotent
4. The callus cells are divided into individual cells and are placed in a new culture medium with a different mix of hormones and nutrients stimulating the development of genetically identical plantlets
5. The plantlets are planted in compost to grow new plants

Question 6

What are the advantages of micropropagation?

Answer 6

• Allows for rapid production of large numbers of plants with known, successful genetic makeup
• Culturing meristems produces disease free plants
• Allows good number of plants to be produced after genetic modification of plant cells
• Infertile plants can be grown
• Way to increase numbers of rare/endangered plants

Question 7

What are the disadvantages to micropropagation?

Answer 7

• Produces a monoculture – plants are genetically identical and susceptible to the same diseases and changed in growing conditions no genetic variation
  
  • Lowers gene pool
• Expensive and requires skilled workers
• If the source material is infected, the clones will be infected too

Question 8

What is embryo twinning and what are its principles?

Answer 8

Embryo Twinning: Splitting an early embryo in half and creating 2 genetically identical embryos

• Artificial embryo twinning splits the early embryos manually into many pieces and each develop into embryos
• This results in the creation of many genetically identical animal clones as the embryos are split from the same original embryo (group of cells) making them clones
• The animals are clones of one another but not clones of the parent used to create the original embryo
  
  • Because a zygote is created with gametes from a male and female which have different genetics
  • So, the embryo has a mix of genetics

Question 9

What is the process of embryo splitting?

Answer 9

1. Female animal with desirable characteristics treated with hormones resulting in the release of many ova (eggs)
2. The ova must be fertilised, either through artificial insemination or within the female
   
   1. The early embryos are then flushed out
3. Whilst the embryonic cells are still totipotent (in the early embryos), they are manually split into smaller embryos
4. The split embryos carry on dividing in vitro (in a lab) to ensure correct development before placing in a surrogate mother
5. Each embryo (if grown correctly) will be placed in the uterus of a surrogate mother so it can grow into a baby animal
6. The embryos develop into foetuses and are born normally to produce genetically identical cloned animals

Question 10

Describe the process of enucleation and SCNT?

Answer 10

Enucleation and Somatic Cell Nuclear Transfer

1. Nucleus removed from a somatic cell of an adult animal
2. An egg cell from a different female of the same species is enucleated
3. The nucleus from the somatic cell is placed into the enucleated egg cell and a mild electric shock is given so they fuse and divide
   
   1. In some cases electrofusion occurs – where the adult somatic cell and the enucleated ovum fuse
4. The embryo that develops is transferred into the uterus of a 3^rd animal to develop
5. The new animal is a clone of the animal from the original somatic cell – but the mtDNA is from the egg cell