SI2 - Plant and Animal Breeding

• Plant and animal breeding is used to improve characteristics to help support sustainable food production.
• Breeders develop crops and animals with: higher food yields, higher nutritional values, pest and disease resistance, the ability to thrive in particular environmental conditions.
• A new plant variety (cultivar) may grow well in the laboratory enviorment however its performance will have to be evaluated in the field trials.
• plant field trials are carried out in a range of environments to: compare the performance of different cultivars ( varieties), compare the effect of different treatments such as fertilisers or pesticides, evaluate GM crops.
• In designing field trials account has to be taken of: the selection of treatments, the number of replicants, and the randomization of treatments.
• The selection of treatments ensure valid comparisons.
• The number of replicants takes account of the variability within the sample.
• the randomisation of treatments eliminates bias when measuring treatment effects.
• over many years farmers and breeders have selected the plants and animals with the best characteristics to be the parent of the next generation - selective breeding
• inbreeding is the mating of closely related individuals.
• In inbreeding, selected related plants or animals are bred for several generations until the population breeds true to the desired type due to the elimination of heterozygotes .
• while inbreeding can be used to develop desired characteristics, there can be negative results.
• A negative result of inbreeding can be an increase in the frequency of individuals who are homozygous for recessive deleterious alleles.
• These individuals will do less well at surviving to reproduce.
• This results in inbreeding depression
• Inbreeding depression can result in a decline in vigour, size, and yield.
• In order to prevent inbreeding depression and to introduce new alleles/characteristics to the plant-animal lines, crossbreeding is carried out.
• New alleles can be introduced to plant and animal lines by crossing a cultivar or breed with an individual with a different, desired genotype.
• In animals, individuals from different breeds may produce a new crossbreed population with improved characteristics- the best characteristics from both breeds.
• The two parent breeds can be maintained to produced more crossbred animals or plants.
• In plants, F1 hybrids produced by the crossing of two different inbreed lines create a relatively uniform hetrozygous
• F1 hybrids often have increased vigour and yeild.
• plants with increased vigor may have increased disease resistance or increased growth rate.
• In inbreeding animals and plants f1 hybrids are not usually bred together as the f2 produced shows too much variation.
• Not all offspring will show the desired characteristics.
• As a result of genome sequencing, organisms with desirable genes can be identified and then used in inbreeding programs to produce offspring with desirable characteristics.
• single genes for desirable characteristics can be inserted into the genomes of crop plants creating genetically modified plants with improved characteristics.
• Breeding programs can involve crop plants that have been genetically modified using recombinant DNA technology
• recombinant DNA technology in plant breeding includes the insertion of BT toxin gene for pest resistance. - insertion of glyphosate resistance gene for herbicide tolerance.