17.5 Artificial selection

The process by which humans select organisms with desired traits to survive and reproduce

Steps

Population has variation

Breeder selects two individuals that exhibit desired characteristics and are compatible

Chosen two individuals are bred together

Offspring are grown to adulthood and those with the most desired characteristics are selected

Process is repeated over generations until all individuals exhibit desired characteristics

Introduction of disease resistance

Plants are screened for resistance and artificially selected

Wheat is bred for resistance to head blight (caused by Fusarium fungus)

Rice is bred for resistance to rice blast (caused by magnaporthe fungus)

Results in increased yield

Inbreeding and hybridisation

Inbreeding increases homozygosity (the more related the parents are, the more alleles they share, and therefore the more likely the offspring are to have the same/duplicate alleles)

Inbreeding depression is when repeated inbreeding causes homozygosity and therefore expression of harmful recessive alleles

Outbreeding produces more heterozygous plants that express fewer harmful recessive alleles (hybrid vigour)

Improving milk yield of dairy cattle

Humans select for cows with high milk yield

However, when artificial selection is no longer applied, average milk yield decreases over generations, indicating that it is a disadvantageous trait at this extreme

Cows with high milk yield are more vulnerable to inflammation and lameness