plant and animal breeding

• improving stocks and crops

  • higher food yield - increase in mass of food produced by wheat crop
  • higher nutritional values - increase in mass of protein in soya bean
  • pest resistance - resistance of tomato to eelworm
  • disease resistance - resistance of potato to late blight
  • ability to thrive in particular conditions - ability of maize to grow in cold, damp climate
• inbreeding

  the fertilisation of gametes from closely related individuals

  selected related organisms are bred for several generations until the population breeds true to the desired type due to elimination of heterozygotes
• result of inbreeding

  • increase in frequency of individuals who are homozygous recessive deleterious alleles
  • they will do less well at surviving to reproduce -> inbreeding depression
• crossbreeding

  In animals, individuals from different breeds may produce a new crossbreed population with desired characteristics. The two parent breeds are maintained to produce more crossbred animals showing the improved characteristic.
• F1 hybrids in plants are produced by the crossing of two different inbred lines to 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.

  When inbreeding animals and plants, F1 hybrids are not usually bred together as the F2 produced show too much variation.
• organisms with desirable genes can be identified and then used in breeding programmes


  recombinant DNA technology allows the introduction of desirable genes from other species

  Eg. - Bt toxin gene from bacteria inserted into plants for pest resistance

  golden rice with added vitamin A
• plant field trials need to be

  valid - measurements that have been made are only affected by one independent variable

  reliable - investigation is repeated and the same results are achieved
• field trial features

  Selection of treatments 

  Randomisation of treatments 

  Number of replicates 
• why do crossbreeding?

  offspring have improved characteristics
• selection of treatments

  to ensure valid comparisons
• randomisation of treatments

  to eliminate bias when measuring treatment effects
• number of replicates

  to take into account of the variability within the sample