Selective Breeding Definition Selective breeding is also known

Selective Breeding

• Definition • Selective breeding is also known as artificial selection. Humans select desirable traits in a species and choose which individuals breed in order to increase these traits in the species. • All crops and domesticated animals today are a product of selective breeding.

Selective breeding vs. natural selection • Natural selection is when certain individuals of a species are “fitter”; they possess alleles which make them more successful in their environment. These individuals survive longer and produce more offspring. Therefore, more of their alleles are passed on to the next generation and over time these alleles become more common in the gene pool • In selective breeding humans determine which phenotypes, and therefore genotypes are desirable in the species. They then increase the alleles for these traits through breeding programs. Often the species produced would be unable to survive in the wild

Selective breeding – nothing new • Agriculture began 10, 000 yrs ago. Humans selected wild varieties of plants and animals with the traits they desired and began selective breeding to increase these desired traits; e. g. to produce bigger, easier to harvest grains with a greater yield • Selective breeding was also used to domesticate animals. Humans killed animals that were aggressive or not cooperative and the only animals left to breed were the ones most docile and easy to handle. Over time this produced “domesticated” animals from wild ones. (Ex. Wolves Dogs)

From Biozone powerpoint ‘cultural evolution’

Selective breeding animals • Belgium Blue cattle – cattle bred to produce a huge amount of muscle (meat). Produced by selecting individuals with a mutation in myostatin gene which results in the production of an increased number of muscle fibers (hyperplasia) • Excess muscle growth begins in utero so calves have to be born by Caesarean section. • Fertilization is almost always by artificial insemination, meaning that sperm can be shipped across continents and only the ‘best’ bulls are selected to breed.

Selective breeding -methods • Inbreeding is reproduction from the mating of parents who are closely related genetically. • Livestock breeders often practice controlled breeding to eliminate undesirable characteristics within a population, which is also coupled with culling (slaughtering) of what is considered unfit offspring, especially when trying to establish a new and desirable trait in the stock. • Repeated test crosses are often used in order to produce pure breeding individuals

Modern corn Ancient corn from Peru (~4000 yrs old) Choosing only the best corn plants for seeds results in better crops over a long time.

S T E P S

Selective breeding - examples • Genome analysis of kiwifruit is being used to selectively breed new, trademarked varieties of fruit with characteristics such as disease resistance. Source: http: //www. plantandfood. co. nz/page/our-research/breedinggenomics/ • Sheep in NZ are being selectively bred to be immune to facial eczema, a fungal disease that can destroy whole flocks. Genome analysis of sheep was carried out and individuals immune to the disease were selected for a breeding program. Source: Ag research NZ

Other Applications of Selective breeding • Breeding programs for endangered species, may involve selection of the least genetically related individuals to breed (to maintain genetic diversity in the species). • Selective breeding programs have resulted in higher yields and better disease resistance in aquaculture species, such as salmon.

Implications of selective breeding • We are concerned with the biological implications of selective breeding that may negatively affect : 1. Ecosystems 2. Genetic biodiversity 3. Health or survival of individuals 4. Survival of populations 5. Evolution of populations Brainstorm some possible (general) implications of selective breeding for each of these.