Selective Breeding & Cloning Notes

Selective Breeding

Selective breeding, also known as artificial selection, involves selecting individuals with desirable characteristics and breeding them together.
The offspring with the desired traits are then selected and bred together.
This process is repeated over many generations to enhance the desired traits.

Plants are selectively bred for:
- Disease resistance
- Increased crop yield
- Ability to survive harsh conditions (e.g., drought tolerance)
- Improved taste of fruits
- Large or unusual flowers
Wild brassica is an example of a plant that has been selectively bred to produce cauliflower, cabbage, broccoli, Brussels sprouts, kale, and kohlrabi.

Animals with desired characteristics are bred together, using multiple parents to avoid inbreeding in subsequent generations.
Offspring exhibiting the desired characteristics are selected and bred together.
This process is repeated for many successive generations.
Animals are commonly selectively bred for:
- High milk and meat yield (cows, goats, and sheep)
- Chickens that lay large eggs
- Specific traits in dogs for hunting, guarding, or companionship.
- Good quality wool in sheep
- Desirable traits in horses such as speed, stamina, strength, intelligence and trainability.
Many breeds of dogs have been selectively bred from wolves.

Select a male bull whose daughters, mothers, or sisters have the highest milk yield.
Choose female cows with the highest milk yield and breed them with the selected bulls.
Select offspring with the highest milk yield and breed them again.
Repeat for many generations.

Dairy cows and Chickens have been selectively bred for many generations to increase milk and meat yield, respectively.

Selective breeding can lead to inbreeding, where closely related animals or plants are bred together.
This reduces genetic variation and increases the risk of genetic disorders.
Reduction in the gene pool and in the number of alleles (different versions of genes) in a population.
The risk of organisms inheriting harmful genetic defects and becoming more vulnerable to new diseases increases due to the reduction in resistant alleles.

Selective breeding is generally easier in plants than in animals because:
- Plants produce more offspring/seeds.
- Plants have shorter life cycles and develop more quickly.
- Plants can be self-pollinated.
- It is easier to control the environment around plants.

Selective Breeding:
- Human involvement: Yes
- Speed of process: Faster
- Survival: Selected by humans
- Characteristics: Desirable to humans
Natural Selection:
- Human involvement: No
- Speed of process: Slower
- Survival: Best adapted survive
- Characteristics: Beneficial for survival

Plant cells can regenerate into a whole new plant given the right hormonal and nutrient conditions. Plants have many stem cells compared to animals.
Plant cells can "de-differentiate" (revert to an unspecialized state) and then "re-differentiate" into various cell types needed to form a new plant.
Micropropagation (tissue culture) is an in vitro (“in glass”) process of propagating plants. The method is as follows:
1. Small pieces of plant tissues (explants) are taken from the parent plant.
2. Explants are sterilized using a disinfectant, rinsed with sterile water, and transferred to a sterile nutrient agar/medium in a petri dish. This medium contains minerals (e.g., magnesium, nitrates), glucose, starch, and amino acids.
3. Explant cells grow into a mass of cells called a callus.
4. The callus is placed in plant growth regulators (auxins) to develop roots, stems, and leaves, becoming plantlets.
5. Plantlets are transferred to individual pots to develop into adult plants.

Since all plants are genetically identical, they are all vulnerable to the same diseases and pests. Lack of genetic variation makes them less able to adapt to changes in the environment.
Requires a sterile laboratory, which can be expensive, and there is a risk of contamination if sterile practices are not followed.

Animal cells are differentiated or specialized so can only form one cell type. Animal cells are specialized and lack the ability to turn back into stem cells, which would be necessary for full regeneration.
Animals have fewer stem cells than plants. Stem cells are primarily found in embryos, bone marrow, and umbilical cords.

A nucleus is taken from a body cell (diploid) of the organism to be cloned.
The nucleus is inserted into an enucleated egg cell (an egg cell with its nucleus removed) from a donor organism.
An electric shock is applied to stimulate cell division.
Mitosis occurs, and the cells divide many times, forming an embryo and cells differentiate.
The embryo is inserted into the uterus of a surrogate mother.

Preserve endangered species.
Produces genetically identical organisms with desirable traits (such as yield, high quality milk, disease resistance).
Cloning can improve agricultural output by enabling faster production.

Lack of genetic diversity, makes them more susceptible to diseases or pests that could wipe out an entire population, may lead to inbreeding in animals.
Ethical concerns such as clones may suffer from developmental abnormalities or reduced life expectancy.
Technically challenging process and expensive and often requires many attempts to get successful clone.

Transgenic means the organism has been given genetic material/gene from a different species
A transgenic animal is bred that contains a foreign gene within its genome.
This process modifies the animal’s genetic makeup to express traits or produce proteins that it wouldn’t naturally have.
This foreign gene causes the animal to produce a useful compound which gets expressed within its milk.

Factor IX is a protein produced naturally in the body. It helps the blood form clots to stop bleeding. Injections of factor IX are used to treat hemophilia (blood clotting disorder).
The human gene for factor IX can be inserted into a goat embryo to form a transgenic animal that produces the protein in its milk.