higher biology - unit 3.2: plant + animal breeding

why is breeding done?

to improve the characteristics to help support sustainable food production

breeders develop crops and animals with...

higher food yields, higher nutritional values, pest + disease resistance and the ability to thrive in particular environmental conditions

why are plant field trials carried out?

to compare the performance of different cultivars or treatments and to evaluate GM crops

plant field trials - selection of treatments to be used

to ensure valid comparisons, only one variable should be altered

plant field trials - number of replicates

to take account of the variability within a sample, more replicates more reliable

plant field trials - randomisation of treatments

to eliminate bias when measuring treatment effects

inbreeding

selected related plants or animals are bred for several generations until the population breeds true to the desired type

what does inbreeding aim to do?

eliminate heterozygotes

what can inbreeding lead to in terms of alleles?

increase in frequency of individuals who are homozygous for recessive deleterious alleles

what can inbreeding result in?

individuals who do less well at surviving to reproduce, resulting in inbreeding depressison

cross breeding

new alleles are introduced to plant and animal lines by crossing a cultivar or breed with an individual with a different, desired genotype

why do we cross breed?

to produce more crossbred animals showing improved characteristics

F1 hybrid

an individual resulting from a cross between two genetically dissimilar parents of the same species

in plants F1 hybrids create...

a relatively uniform heterozygous crop

F1 hybrids have increased...

vigour and yield

plants with increased vigour may have increased...

disease resistance or increased growth rate

what is wrong with F2 hybrids?

F2 produced shows too much variation and may lack the improved characteristics

breeding programmes can involve crop plants that have been genetically modified using...

recombinant DNA technology

as a result of genome sequencing, organisms with desirable genes can be...

identified and then used in breeding programmes