ka2: plant and animal breeding

• Plant and animal breeding 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 and ability to thrive in particular environmental conditions
• Plant field trials are carried out in a range of environments to compare the performance of different cultivars or treatments and to evaluate GM crops.
• In designing field trials account has to be taken of the selection of treatments, the number of replicates and the randomisation of treatments.
• • The selection of treatments to ensure valid comparisons, the number of replicates to take account of the variability within the sample, and the randomisation of treatments to eliminate bias when measuring treatment effects.
• Inbreeding 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.
• Analysis of patterns of inheritance in inbreeding using monohybrid crosses.
• A 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.
• Cross breeding and F1 hybrids

  In animals, individuals from different breeds may produce a new crossbreed population with improved characteristics. The two parent breeds can be maintained to produce more crossbred animals showing the improved characteristic.
• 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 plants, F1 hybrids, produced by the crossing of two different inbred lines, create a relatively uniform heterozygous crop. F1 hybrids often have increased vigour and yield.
• Plants with increased vigour 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.
• As a result of genome sequencing, organisms with desirable genes can be identified and then used in breeding programmes.
• Single genes for desirable characteristics can be inserted into the genomes of crop plants, creating genetically modified plants with improved characteristics.
• Breeding programmes can involve crop plants that have been genetically modified using recombinant DNA technology.
• Details of recombinant DNA technology techniques in improving crop plants are not required, for example the use of Agrobacterium.
• Recombinant DNA technology in plant breeding includes insertion of Bt toxin gene into plants for pest resistance, glyphosate resistance gene inserted for herbicide tolerance.
• Plant and Animal Breeding

  Breeders of crops and livestock have been manipulating heredity (passing on of traits to offspring) for hundreds of thousands of years. This has been done to improve plant crops, improve animal stock and to support sustainable food production.

   

  Over time breeders have developed:

  • Improved crops and animals with higher food yields.
  • Crops and animals with higher nutritional values.
  • Pest and disease resistance.
  • The ability to thrive in particular environmental conditions.
• 1. Plant Field Trials

  A plant field trial is a type of investigation, set up in a range of environments to:

   

  • Compare the performance of different plant cultivars or treatments (e.g. conventional versus GM) under the same set of experimental conditions.

   

  • Evaluate GM crops.
• 1. Designing a plant field trial

  Once you have decided what is to be investigated the following factors must be considered:

   

  • Selection of treatments to be used – to ensure valid comparisons.

   

  • Number of replicates to be included – to take account of the variability within the sample. A larger number increases reliability.

   

  • Randomisation of treatments – to eliminate bias when measuring treatment effects.
• Inbreeding


  The fusion of two gametes from close relatives
• Inbreeding

  • Ensures that the members of each generation of a selectively bred strain receive alleles for the desired characteristic
  • Can also lead to loss of heterozygosity and inbreeding depression
• Loss of heterozygosity

  Continuous inbreeding leads to a loss of heterozygosity and development of homozygosity
• Inbreeding depression

  If a natural out-breeder is forced to inbreed, an inbreeding depression can occur due to the accumulation of homozygous recessive alleles which can be deleterious (harmful)
• Inbreeding depression


  • Appears as a decline in vigour, size, fertility and yield of the plant or animal
• Inbreeding is naturally occurring in some species of self-pollinating plants e.g. peas, wheat and rice
• Self-pollinating plants are less susceptible to inbreeding depression due to the elimination of deleterious alleles by natural selection
• Inbreeding cannot be carried out indefinitely; eventually deleterious alleles will accumulate and cause an inbreeding depression
• 1. F1 Hybrids

  In plants, F1 hybrids, produced by the crossing of two different inbred lines, create a relatively uniform heterozygous crop.

   

  F1 hybrids often have increased vigour and yield. Increased vigour will provide increased disease resistance and/or increased growth rate.

   

  The F2 generation created from these F1 hybrids is genetically variable and of little use for further production (flowers may be different heights, and petals may be different colours) although it can provide a source of new varieties.
• Cross breeding

  Introducing new alleles to plant and animal lines by crossing a cultivar or breeding with an individual with a different, desired genotype
• Cross breeding in animals

  • Different breeds of sheep show variation in their fertility, rate of meat production, disease resistance and wool quality
• Cross breeding process

  1. Individuals from different breeds mate

  2. Offspring are known as the F1 hybrid

  3. Offspring receive half their genetic information from one parent and half from the other

  4. The two parent breeds can be maintained to produce more crossbred animals showing the improved characteristic
• Genetic technology

  • Genome sequencing
  • Genetic transformation techniques
  • Recombinant DNA technology
• Genome sequencing


  Organisms with desirable genes can be identified and then used in breeding programmes
• Genetic transformation techniques

  A single gene for a desirable characteristic can be inserted into the genome of crop plants
• Genetically modified plants


  Plants with improved characteristics
• Recombinant DNA technology


  Crop plants have been genetically modified
• Insertion of Bt toxin gene into plants

  • Pest resistance
• Glyphosate resistance gene inserted

  • Herbicide tolerance