5 Selective breeding Flashcards
What happened around 12 000 years ago?
The human way of life changed significantly.
What did humans begin to do?
Humans began to grow plants and keep animals for milk and meat. They became farmers rather than hunters.
What have humans tried to do ever since the cultivation of the first wheat and barley and the domestication of the first stock animal?
Humans have tried to obtain bigger yields from them.
How did they attempt to do this with plants?
They cross-bred different maize plants (and barley plants) to obtain strains that produced more grain.
How did they attempt to do this with animals?
They bred sheep and goats to give more milk and meat – selective breeding had begun.
What are animals and plants used for today?
Today, animals and plants are bred for more than just food. For example, animals are used to produce a range of medicines and for research into the action of drugs.
What is selective breeding?
It is the process where humans cross-
breed individual animals or plants that have been chosen because they show certain characteristics. Used to produce domestic animals and crop plants. Also known as artificial selection.
Why is it nicknamed artificial selection?
It is sometimes called ‘artificial selection’, as human choice, rather than environmental factors, is providing the selection pressure.
What does modern gene technology enable us to do in terms of selective breeding?
Modern gene technology makes it possible to create a new strain of plant within weeks, rather than years.
What has traditional selective breeding been used on?
- Plants.
- Animals.
How did farmers use traditional selective breeding on plants?
Traditionally, farmers have bred crop plants of all kinds to obtain increased
yields. Probably the earliest example of selective breeding was the cross-
breeding of strains of wild wheat.
What was this aim of selective breeding?
The aim was to produce wheat with a much increased yield of grain and with shorter, stronger stems.
Where was this wheat used?
This wheat was used to make bread.
What is an image that shows how modern wheat is the result of selective breeding by early farmers?
Is it only just wheat that has been used in selective breeding?
Other plants have been selectively bred for certain characteristics.
What is an example of another plant that has been selectively bred for certain characteristics?
One species of wild brassica (Brassica olera) was selectively bred to give several strains, each with specific features.
What is brassica?
Brassica is a genus of cabbage-like plants.
What were the characteristics of some of the brassica strains?
Some of the strains had large leaves, others had large flower heads, and others produced large buds.
What is a diagram which shows the process of selectively breeding the original wild brassica plants to enhance certain features and how it has produced several familiar vegetables?
What kind of vegetables have been produced by selective breeding?
Selective breeding has produced many familiar vegetables.
What are some examples of these vegetables?
Besides the ones produced from Brassica, selective breeding of wild Solanum plants has produced the many strains of potatoes that are eaten today. Carrots and parsnips are also the result of selective breeding programmes.
What type of strains are crop plants bred to produce?
- Give higher yields.
- Are resistant to certain diseases (the diseases would reduce the yields).
- Are resistant to certain insect pest damage (the damage would reduce the yield).
- Are hardier (so that they survive in harsher climates or are productive for
longer periods of the year). - Have a better balance of nutrients in the crop (for example, plants that
contain more of the types of amino acids needed by humans).
What is a diagram that shows a field of potato plants?
What is an explanation of this divide of the potato plants?
The plants on the right have been
bred to be resistant to a fungal pest. Plants on the left are not resistant to the pest.
Why do farmers breed stock animals?
For similar reasons to the breeding of crops.
Which are desirable characteristics that animals are selectively bred to produce?
- Produce more meat, milk or eggs.
- Produce more fur or better quality fur.
- Produce more offspring.
- Show increased resistance to diseases and parasites.
Is breeding animals new?
No, it has been practised for thousands of years.
For many thousands of years, what was the only way to improve livestock?
It was to mate a male and a female with the features that were desired in the offspring.
What is a desirable trait in cattle?
A high milk yield.
How would cattle be selectively bred for a high milk yield?
In cattle, milk yield is an important factor and so high-yielding cows would be bred with bulls from other high-yielding cows.
What technique has become widely available?
Since about 1950, the technique of artificial insemination has become widely available.
What is artificial insemination?
It is a method of selective breeding, where semen is used to make an animal pregnant without sexual intercourse. e.g. using semen from prize bulls to inseminate cows.
How is artificial insemination used with bulls?
Bulls with many desirable features are kept and semen is obtained from them.
What is done with the semen of bulls?
The semen is diluted, frozen and stored.
Where does this semen then go?
Farmers can buy quantities of this semen to inseminate their cows.
How is the farmer then able to inseminate their cows?
The semen is transferred into
the cow’s uterus using a syringe.
What does artificial insemination allow us to do in terms of cows?
AI makes it possible for the semen from one prize bull to be used to fertilise many thousands of cows.
What are certain farm animals (sheep and pigs) in terms of domestication?
Modern sheep are domesticated wild sheep, and pigs have been derived from wild boars.
How are there many varieties of dogs that now exist?
All these have been derived from one ancestral type. This original ‘dog’ was a domesticated wolf.
What is an image that shows how the many different breeds of dog all originate from a common ancestor - the wolf?
What happened in domesticating the wolf?
Humans gained an animal that was
capable of herding stock animals.
What is an example of how certain characteristics are able to be ‘bred out’?
The sheepdog has all the same instincts as the wolf except the instinct to kill. This has been selectively ‘bred out’.
