Selective Breeding

Selective breeding has created many plant and animal varieties with characteristics that are desirable to humans. This has been fundamental in allowing us to feed such a large and growing population. Most selectively bred breeds and varieties would no longer survive in the wild. Why not? Natural selection ensures species change in response to changes in environment Artificial selection means that new varieties of a species are created in response to the desires of humans Selective Breeding

Selective Breeding in cattle The wild auroch (Bos primigenius) 6000 BC – Asia & Africa Extinct in 1627 Life span ~ 25 years ~3L of milk per day when calves are suckling From around 6000 BC they have been gradually domesticated through selective breeding to create modern cattle breeds.

Modern cattle (Bos Taurus) are a domesticated ‘version’ of this original beast. Dairy & beef cattle are the same species but different breeds. Each breed has been created to have particular characteristics. Dairy – 35L of milk per day! Calves removed from mothers after a couple of days. Beef – Some have so much muscle (meat) they can barely stand up and suffer from joint problems like arthritis. Slaughtered at 5 years old Holstein-Friesian Selective Breeding in cattle 90% of dairy cows in Europe are this breed. Very little genetic diversity.

The ‘Belgian Blue’

Chickens were domesticated from wild Jungle Fowl, which still exist in India, some 3400 years ago. They lay eggs per year. Different breeds of chicken are bred with different characteristics. Selective Breeding in chickens

Egg-laying chickens lay around 300 eggs each year. They need to be fed special high-calcium diets so they can make the egg shells, but even so they tend to suffer from bone disease due to a lack of calcium. Meat chickens (broilers) are bred to grow quickly and have large leg and breast muscles. Their fast growth makes them susceptible to infectious disease and they also suffer joint problems.

Potatoes originated from Peru. They were first "domesticated" around years ago and introduced to Europe in 1536 Many wild varieties are poisonous (they belong to the nightshade family). Selective breeding has developed hundreds of different varieties with a range of characteristics. All modern crop plants have been selectively bred from natural species

Selective Breeding – basic principles From existing stock, select individuals with the best characteristics (e.g. highest milk yield) as they must have the right alleles for this Breed them with each other Select the best of the offspring and breed them together Repeat over several generations. The desirable trait will become more prominent and undesirable traits will disappear from the population.

Complete questions 1, 3 & 4 from page 225 of the text book If you have time, discuss question 5 in small groups and then as a class

A reminder - Evolution in cats The cat family has evolved due to different selection pressures acting on different populations. Changes in predators, prey, competition, climate and the physical environment can all apply selective pressures on a population. Alleles which confer an advantage will be passed to the next generation & become more common – leading to changes in the species over many generations. Natural selection drives speciation in this way.

proailurus lemanensis The ‘first cat’ 25 mya in Eurasia Snow Leopard - Panthera uncia Bengal Tiger - Panthera tigris tigris Variation in a population is created by mutation & sexual reproduction Isolation of populations and changes in the environment apply selective pressures Natural selection means that the most favourable alleles are passed to the next generation Species evolve over time and new species arise as a result