Artifical Selection

Artificial Selection Artificial selection is the deliberate selection of organisms with desirable characteristics that are useful to humans  Humans determine which alleles pass onto successive generations.

Selective breeding Useful varieties of plants and animals have been derived from species by selective breeding

Selective breeding Cattle have been bred for Plants Quantity and quality of meat Milk yield Butterfat content of milk Plants Increasing yield of crops Disease resistance

Inbreeding depression Reduction in variation of alleles in the population Increase risk of homozygosity (harmful recessive genes)

hybridisation. Hybrid Individual resulting from a cross of two genetically dissimilar parents of the same species Hybrid vigour – some offspring produced are stronger (“fitter”) than either parent. Re-establishes heterozygosity.

Hybridisation in Farm Animals Hybrid vigour in cattle Improved birth weight Improved feed conversion efficiency Sheep Scottish blackface x French strain Hybrid has improved meat yield and quality

Genetic Engineering

Genetic Engineering (Recombinant DNA technology) Genome haploid set of chromosomes typical of a species Recombinant DNA technology involves transferring genes from the genome of one organism to the genome of another.

Location of genes Recognition of characteristic banding patterns on chromosomes Giant chromosomes take up stains producing distinctive bands Banding pattern is a constant characteristic of each type of chromosome Example – red/white eye colour in fruit fly Gene probes Short length of chemically labelled single sided DNA Complementary to the gene that the genetic engineers wish to locate DNA is cut into fragments and the gene probe attaches to required gene

Genetic Engineering Select a gene for desirable characteristics Select a suitable vector Splice the gene into the DNA of the vector Insert vector into host cell Host cell propagated

Enzymes involved Endonuclease Ligase Used to cut DNA into fragments and open bacterial plasmids Recognizes a particular sequence of bases on DNA and makes its cuts at these sites. Ligase Seals “sticky ends” Seals DNA fragment into bacterial plasmid

Vector Recombinant plasmids carry DNA from genome of one organism into that of another.

Antibiotic Recombinant plasmid also contains a gene coding for anti-biotic resistance

Useful products Insulin production interferon Human growth hormone production

Transgenic crops  Agrobacterium tumefaciens can inject a plasmid into plant cells, the plasmid’s genetic material can become incorporated into the plant’s DNA. Scientists use this bacteria to insert desirable genes into plants. These plants are transgenic varieties. e.g. gene inserted to produce an insecticide protein, the leaves of the plant can resist attack by caterpillars.

Crop plants Other inserted genes in plants block production of chemicals which promote ripening resistance to weed killer production of antifreeze chemical block enzyme production ability to fix nitrogen resistance to drought

Farm animals genetically modified to produce human proteins Examples blood clotting factor Eggs that contain anti-bodies needed for cancer fighting drugs

somatic fusion Somatic fusion allows a fertile hybrid to be formed from two species. Protoplasts from two different species are prepared by having their cell walls removed. These protoplasts fused to form hybrid protoplast. Somatic hybrid cell is induced to form a cell wall Hybrid cell divides into a callus (undifferentiated cell mass) Calluses develop into hybrid plants containing mixture of parents’ genetic traits.

Resistance to potato leaf roll Through somatic fusion a potato plant has been produced which is tuber bearing and resistant to potato leaf roll virus.