Selective Breeding
Selective breeding: the breeding of only those individuals with desirable features. AKA artificial selection
Selective breeding in plants
eg. wheat – increased yield of grain and shorter, stronger stems – used to make bread
Crop plants are selectively bred that:
give higher yields
are resistant to certain diseases
Are resistant to certain insect pest damage
are hardier
have a better balance of nutrients in the crop
Selective breeding in animals
Selected for animals that
produce more meat, milk or eggs
produce more or better quality fur
produce more offspring
show increased resistance to diseases and parasites
Artificial insemination
Bulls with desirable features are kept and semen is obtained from them
Semen is diluted, frozen and stored
Farmers can buy quantities of this semen to inseminate their cows
Semen transferred into the cow's uterus using a syringe
A prize bull can inseminate thousands of cows
eg. sheepdog – a wolf where the instinct to kill has been bred out
Cloning in plants
Any procedure that produces genetically identical offspring
Taking cuttings
- tear off a side shoot from the plant
- dip the side shoot in rooting powder
- plant in compost
- place under glass – 'mini greenhouse' creates warm environment to speed up growth and a humid one to reduce water loss from leaves
Any differences will be environmental
Micropropagation
- remove tips of stems and side shoots, KA explants
- explants are trimmed to 0.5-1mm, and surface-sterilised to kill any microorganisms
- place in sterile agar medium containing nutrients and plant hormones to encourage growth
- more explants can be taken from new shoots until demand is satisfied
- explants with shoots transferred to another culture medium with a different balance of plant hormones to induce root formation
- explants with roots transferred to greenhouses and transplanted into compost and gradually acclimatised to normal growing conditions
Advantages of micropropagation
Large numbers can be produced rapidly
Species that are difficult to grow from seed or cuttings can be propagated like this
Plants can be produced at any time of year
Large numbers of plants can be stored easily
Genetic modifications can be introduced into thousands of plants quickly after modifying only a few plants
Cloning Animals
- mammary gland cells removed and cultured from parent sheep
- unfertilised egg taken from egg donor sheep and nucleus removed
- fuse the two cells with an electric current
- cell develops into embryo
- embryo transferred into surrogate mother
- lamb born is identical to the parent sheep
Making proteins
Cloning animals is useful if they produce an important product
Sheep have been genetically modified to produce human proteins, eg. alpha-1-antitrypsin – used to treat emphysema and cystic fibrosis
Animals that have had genes transferred from other species are KA transgenic