17.2. Artificial Selection Flashcards
Artificial Selection
When humans purposefully apply selection pressures to populations,
Selective Breeding
humans use animal breeding and plant breeding to selectively develop particular phenotypic traits by choosing which typically animal or plant males and females will sexually reproduce and have offspring together.
Inbreeding
Mating of organisms closely related by ancestry. It goes against the biological aim of mating, which is the shuffling of DNA
Outbreeding
Crossing between different breeds and no common ancestors
Hybridisation
The process of mating organisms of different varieties or species to create a hybrid
Inbreeding depression
reduced biological fitness in a given population as a result of inbreeding, or breeding of related individuals
Biological fitness
an organism’s ability to survive and perpetuate its genetic material. due to increased homozygosity
Hybrid Vigour
improved activity and survival of hybrid offspring
Breeding Cattle with High Milk Yields
- dairy cattle are cattle kept for milk production
- only females produce milk
- selective breeding is therefore done using cows with high milk yields and bulls whose female relatives (mothers, sisters) have high milk yields
- if a particular bull is proved to have many female offspring with high milk yields, then semen would be taken from the bull to inseminate many cows
- selective breeding has produced massive increases in the volume and quality of milk produced by cows
- however, such intensive selective breeding can inadvertently cause health problems for the cattle
Breeding disease-resistant varieties of wheat and rice
- farmers may want to have rice or wheat plants that produce large yields of grain and that are resistant to fungal diseases like rust
- they want plants to be short, so more can be put into the growing grain rather than wasted on stems, and so plants
- breeders can choose a wheat or rice plant that is short, with high yields of grain, and another that does not have these characteristics but is very resistant to rust
- pollen from one plant is taken and put on the stigma of another plant
- the resulting seeds are collected and sown
- the plants that show the best combination of desired characteristics are bred together
- this continues for several generations, until the breeder has a population with high yield and high resistance to dust
Breeding dwarf varieties of crop plants
- gibberellin causes plants to grow longer
- some varieties of crop plants have mutant alleles of the gibberellin gene, and do not produce as much gibberellin
- the dwarf plants are often higher yielding, as they do not waste energy growing tall
- they can also stand upright in strong winds or heavy rain
Inbreeding and hybridisation in maize
- farmers require crops that are all genetically identical
- if the seed is sown at the same time and in the same conditions, the plant will grow uniformly
- harvesting would be easier if this is the case as grain all have similar characteristics
- genetic uniformity is achieved through inbreeding for many generations
- However, inbreeding results in weak plants with low yields. This is inbreeding depression
- maize breeding therefore involves producing hybrids between 2 inbred lines
- inbred lines of maize with desirable traits are identified and crossed
- the best of the hybrids are chosen for commercial production
Difference between natural and artificial selection
- artificial is similar to natural selection, in that individuals with particular characteristics are more likely to breed than others
- However, in artificial selection, individuals without these characteristics will not breed at all, whereas in natural selection there is chance that they might breed
- artificial selection may therefore produce bigger changes in fewer generations than natural selection normally does
- Artificial selection usually requires many generations into the desired result is obtained
