Plant and animal breeding

Why do breeders try to improve their produce (crops and/or livestock)?

Sustainable food production

In what two ways do breeders try to improve their produce (crops and/or livestock)?

Careful breeding or genetic technology

What are five improvements that can be made to crops and/or livestock?

• Ability to thrive in certain conditions

• Increase in nutritional value

• Increase in yield

• Resistance to disease

• Resistance to pests

What are two examples of careful breeding?

Inbreeding, and cross breeding and F1 hybrids

Inbreeding

The fusion of two gametes from close relatives

Outbreeding

The fusion of two gametes from unrelated members of the same species

Diagram: breeding

Gametes

Sex cells

How many times are selected related animals or plants with desired characteristics bred for?

Several generations until the population breeds true to the desired characteristic due to the elimination of heterozygotes

Example: heterozygotes (alleles)

Aa

Example: dominant homozygotes (alleles)

AA

Example: recessive homozygotes (alleles)

aa

Inbreeding depression

When a natural outbreeder is forcibly inbred

What causes inbreeding depression?

The genotypes that emerge are homozygous for an accumulation of recessive deleterious (harmful) alleles

What four things does inbreeding depression result in?

• Decreased fertility

• Decreased size

• Decreased vigour (the size and speed of which a plant grows)

• Decreased yield

Genotype

The alleles that an organism has for a particular characteristic

How can new alleles be introduced to animal and plant lines?

Crossing a breed or a cultivar with an individual with a different desired genotype

A crossbreed

When two individuals from different breeds are bred together to produce a new crossbred population with improved characteristics

Crossbreeding and F1 hybrids in animals

The two parent breeds can be maintained to produce more crossbred animals showing the improved desired characteristic

Diagram: cross breeding and F1 hybrids

Crossbreeding and F1 hybrids in plants

F1 hybrids produced by the crossing of two different inbred lines creates a relatively uniform heterozygote crop, often with increased vigour and yield

Why are F1 hybrids of animals and plants not usually bred together?

F2 generations show too much variation

Hybrid vigour

A phenomenon where hybrid offspring exhibit superior characteristics compared to their purebred parents

Genetic technology

Organisms with desired genes can be identified and used in breeding programmes as a result of genomic sequencing

Genetic transformation techniques

When the gene for a desired characteristic in one crop plant is inserted into the genome of another crop plant

Example: genetic transformation technique

DNA sealed in a bacterial plasmid which acts as a vector

Vectors

A DNA molecule used to carry foreign genetic information into another cell in recombinant DNA technology

What is the purpose of using genetic transformation techniques?

To make GM (genetically modified) plants with improved characteristics

What can breeding programmes involve?

Crop plants that have been genetically modified using recombinant DNA technology

Recombinant DNA technology

A technique used to mass produce proteins like insulin by genetically altering bacteria to incorporate the necessary human genes to express the desired hormones

Example: recombinant DNA technology (Bt toxin)

The bacterial gene for Bt toxin is extracted from one crop and inserted into another which will then produce their own Bt toxin, making them resistant to certain insects

Diagram: a plant field trial

What three things are plant field trials used for?

• To compare the performance of two different plant cultivars under the same set of environmental conditions

• To evaluate GM crops

• To see the effect of different environmental conditions or treatments on a new cultivar of crop plant

Cultivar

A crop plant that has been produced in cultivation by selective breeding

Selective breeding

Choosing two parents with particular characteristics and breeding them together to produce offspring with a variety of desired characteristics

What are the three design features of a plant field trial?

• Inclusion of several replicates - takes account of the variability within the sample

• Randomisation of treatments - prevents bias when measuring the treatments affects

• Selection of treatments - ensures a valid comparison

Alleles

A different form of the same gene

What determines an individuals alleles?

By the individuals parents inheritance