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**Explain****, using an appropriate example from agriculture, why selective breeding has been practiced** GCB 7.5
 * Selective breeding has been practiced for thousands of years. It involves humans choosing two individuals to mate to produce offspring with certain desirable characteristics, such as leaner meat on an animal or wheat seeds that remain attached to the plant for longer. Many plants and animals for domestic and agricultural purposes have been bred in this way to produce new varieties.
 * Analyse and present information from secondary sources to trace the history of the selective breeding of one species for agricultural purposes and use available evidence to describe the series of changes that have occurred in the species as a result of this selective breeding**

Over the centuries humans have tried to breed better crops and livestock. Traditionally this was done by carefully choosing parents for breeding that show the required characteristics - **selective breeding**.
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= **Selective breeding** = **These are the steps in selective breeding:**
 * 1) **Decide which characteristics are important**
 * 2) **Choose parents that show these characteristics**
 * 3) **Select the best offspring from parents to breed the next generation**
 * 4) **Repeat the process continuously**

Dairy cattle
-Holstein breed originated in Europe. The major historical developement of this breed occured about 2000 years ago in the Netherlands. original stock were the black animals and white animals of the Batavians and Friesians. Holsteins were bred and strictly culled to obtain animals which would make best use of grass, the area's most abundant resource -Jersey cow milk is ideal for making butter because it is so creamy.
 * cross with**

Selective breeding has been used throughout history to improve the quality and yield of plants and animals. Similarly, cross-breeding has been used to emphasis particular favourable genetic traits. by trial and error, hybrids of Friesians and jersey cows that produce creamier milk have been developed.

However selective breeding relies on sexual reproduction and cannot prevent some genetic variability taking place. It also only allows for the exchange of genes between a species. Modern technology has allowed desirable characteristics and traits on spaecific genes to be transferred, not only within a species but also to different species. This proccess is faster than selective breeding.

Fifty years ago, cows used to produce around 400 kg of milk per lactation. As a result of breeding programs, the average cows have increased their yields to 8000kg of milk per lactation. Most dairy farmers breed their cows using artificial insemination to produce crosses that give higher milk yields. Lower yielding cows are generally herded to produce offspring for meat production.

Notes: -Increasing milk yield by selecting bulls from high yield herds and breeding them with cows that have the best milk production. breeding jersey cows(creamy milk) with friesian cow(lots of milk)