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

  1. tear off a side shoot from the plant
  1. dip the side shoot in rooting powder
  1. plant in compost
  1. 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

  1. remove tips of stems and side shoots, KA explants
  1. explants are trimmed to 0.5-1mm, and surface-sterilised to kill any microorganisms
  1. place in sterile agar medium containing nutrients and plant hormones to encourage growth
  1. more explants can be taken from new shoots until demand is satisfied
  1. explants with shoots transferred to another culture medium with a different balance of plant hormones to induce root formation
  1. 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

  1. mammary gland cells removed and cultured from parent sheep
  1. unfertilised egg taken from egg donor sheep and nucleus removed
  1. fuse the two cells with an electric current
  1. cell develops into embryo
  1. embryo transferred into surrogate mother
  1. 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