Selective breeding + TRIPLE: cloning

What is selective breeding?

Process where humans choose individual organisms/offsprings showing the desired characteristics and cross-breed them over many generations

Explain examples of desired characteristics in crop plants

• Give higher yields

• Are resistant to certain diseases (diseases would reduce yield)

• Are resistant to certain insect pest damage (the damage would reduce yield)

• Are hardier (so that they survive in harsher climates or are productive for longer periods of the year)

• Have a better balance of nutrients in the crop (e.g plants that contain more of the types of amino acids needed by humans)

Explain examples of desired characteristics in stock animals

• Produce more meat, milk or eggs

• Produce more fur or better quality fur

• Produce more offspring

• Show increased resistance to diseases and parasites

Describe the process of selective breeding

• Organisms with desired characteristics are chosen by humans

• Humans cross them together

• Look for desired characteristic in offspring

• Breed from those offspring that have the desired characteristic

• Repeat over several generations

Example of animal and plant selective breeding

• Wheat → for increased yield of grain and shorter, stronger stems

• Cattle (cows) → for greater milk yield

How are cows selectively bred for higher milk yield?

High milk yielding cows are bred with bulls from other high yielding cows

What is artificial insemination (AI) and when was it made widely available?d

• Bulls (or any animal really) with many desirable features are kept and semen is obtained from them.

• The semen is diluted, frozen and stored.

• Farmers can buy quantities of this semen to inseminate their cows by transferring the semen with a syringe into the cow’s uterus

• AI makes it possible for the semen from one prize bull to be used to fertilise many thousands of cows

1950

TRIPLE (ya no hay más double): Modern selective breeding: cloning

What is a clone? What is cloning? Examples of cloning?

Groups of cells or organisms that are genetically identical

A procedure that produces genetically identical offspring

• Taking cuttings of plants are growing them

• Micropropagation

Describe how taking a cuttings result in genetically identical plants

Why might some cuttings NOT be genetically identical?

• All cuttings contain identical genes as they are all from the same parent plant

• They form new cells by mitosis (each new cell contains the exact genetic material as it produces diploid cells)

• Many garden flowers have been propagated this way

• Due to the environment (some might receive less light)

What is micropropagation?

Growing plants from small pieces of plant tissue in vitro (in test tubes/agar and under controlled conditions)

What does in vitro mean?

Outside a living organism

Describe the process of micropropagation

• Take small pieces of tissue (explants)

• Sterilise (surface of explants)

• Place into sterile agar

• Provide minerals (e.g nitrate)/glucose/amino acids

  • Ignore nutrient

• Plant growth substances/auxin/hormones

• (this is not in ms but should be) the growth medium encourages explant cells to grow and divide into small masses of cells (callus)

• each callus is transferred to another culture medium containing a range of plant growth hormones

• This causes them to develop roots (and stems and leaves) forming a plantlet

• Plantlet can be transferred to potting trays in compost

Where should newly made plantlets be stored for growth? Why?

Greenhouses

The atmosphere in greenhouses is kept very moist to reduce water loss from the young plants.

• Because of the amount of vapour in the air these are often called fogging greenhouses

Why is it possible for small pieces of plant tissue (explants) to grow into whole new individual plants but small tissue from animals won’t?

Plant cells can differentiate into all different specialised cell types throughout a plants’ life

In animals, only stem cells found in animal embryos can differentiate into all the specialised cell types required to make a whole new individual

What are the advantages of micropropagation?

• Large numbers of genetically identical clones of plants with desired traits can be produced (this is not that good of a point, you could merge this with ‘quickly’)

• Large quantities can be produced rapidly (plantlets grow into mature plants quicker than seeds)

• Can be done at any time of the year (ALWAYS SAY THIS ONE)

• Large numbers of plants can be stored easily (many can be kept in cold storages at the early stages of production and then developed as required)

  • This might be used to preserve a rare plant species

Disadvantages of micropropagation?

Trained personnel and a sterile laboratory are required

All the plants produced are genetically identical and so will all be vulnerable to the same diseases and pests (lack of genetic variation makes them less able to adapt to environmental change)

Describe the stages in the production of cloned mammals

• The nucleus of a diploid body cell from the animal is taken

• The nucleus is then placed into an enucleated egg cell (the nucleus containing the genetic material from donor animal has been removed)

• An electric shock is used to help the cell to divide by mitosis

• This develops into an embryo

• This is then placed into the uterus of the surrogate mother

Dolly the sheep was produced/cloned after many unsuccessful attempts.

What might the unsuccessful attempts been like? What did biologists believe these problems were due to?

• Deformed

• Did not survive to birth

The genes came from an animal that had already lived for several years and from cells specialised to do other things other than produce sex cells

What benefit does cloning give humans (apart from commercial benefits)?

• A transgenic animal has a foreign gene that codes for a useful human protein which the animal can then produce in its milk, eggs or blood

• This human protein can be used for medical purposes (e.g proteins that treat diseases in humans)

• The transgenic animal can be cloned to produce more animals with the same trait

END OF TRIPLE: Explain an example of a transgenic ANIMAL cloned to produce a useful human protein to treat a specific disease

Sheep have been genetically modified to produce several human protein including one that is used to treat emphysema.

The GM sheep secrete this protein in their milk

Cloning these sheep would allow an increased production of this protein