5 Selective breeding

Question 1

What happened around 12 000 years ago?

Answer 1

The human way of life changed significantly.

Question 2

What did humans begin to do?

Answer 2

Humans began to grow plants and keep animals for milk and meat. They became farmers rather than hunters.

Question 3

What have humans tried to do ever since the cultivation of the first wheat and barley and the domestication of the first stock animal?

Answer 3

Humans have tried to obtain bigger yields from them.

Question 4

How did they attempt to do this with plants?

Answer 4

They cross-bred different maize plants (and barley plants) to obtain strains that produced more grain.

Question 5

How did they attempt to do this with animals?

Answer 5

They bred sheep and goats to give more milk and meat – selective breeding had begun.

Question 6

What are animals and plants used for today?

Answer 6

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.

Question 7

What is selective breeding?

Answer 7

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.

Question 8

Why is it nicknamed artificial selection?

Answer 8

It is sometimes called ‘artificial selection’, as human choice, rather than environmental factors, is providing the selection pressure.

Question 9

What does modern gene technology enable us to do in terms of selective breeding?

Answer 9

Modern gene technology makes it possible to create a new strain of plant within weeks, rather than years.

Question 10

What has traditional selective breeding been used on?

Answer 10

• Plants.
• Animals.

Question 11

How did farmers use traditional selective breeding on plants?

Answer 11

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.

Question 12

What was this aim of selective breeding?

Answer 12

The aim was to produce wheat with a much increased yield of grain and with shorter, stronger stems.

Question 13

Where was this wheat used?

Answer 13

This wheat was used to make bread.

Question 14

What is an image that shows how modern wheat is the result of selective breeding by early farmers?

Answer 14

Question 15

Is it only just wheat that has been used in selective breeding?

Answer 15

Other plants have been selectively bred for certain characteristics.

Question 16

What is an example of another plant that has been selectively bred for certain characteristics?

Answer 16

One species of wild brassica (Brassica olera) was selectively bred to give several strains, each with specific features.

Question 17

What is brassica?

Answer 17

Brassica is a genus of cabbage-like plants.

Question 18

What were the characteristics of some of the brassica strains?

Answer 18

Some of the strains had large leaves, others had large flower heads, and others produced large buds.

Question 19

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?

Answer 19

Question 20

What kind of vegetables have been produced by selective breeding?

Answer 20

Selective breeding has produced many familiar vegetables.

Question 21

What are some examples of these vegetables?

Answer 21

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.

Question 22

What type of strains are crop plants bred to produce?

Answer 22

• 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).

Question 23

What is a diagram that shows a field of potato plants?

Answer 23

Question 24

What is an explanation of this divide of the potato plants?

Answer 24

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.

Question 25

Why do farmers breed stock animals?

Answer 25

For similar reasons to the breeding of crops.

Question 26

Which are desirable characteristics that animals are selectively bred to produce?

Answer 26

• Produce more meat, milk or eggs.
• Produce more fur or better quality fur.
• Produce more offspring.
• Show increased resistance to diseases and parasites.

Question 27

Is breeding animals new?

Answer 27

No, it has been practised for thousands of years.

Question 28

For many thousands of years, what was the only way to improve livestock?

Answer 28

It was to mate a male and a female with the features that were desired in the offspring.

Question 29

What is a desirable trait in cattle?

Answer 29

A high milk yield.

Question 30

How would cattle be selectively bred for a high milk yield?

Answer 30

In cattle, milk yield is an important factor and so high-yielding cows would be bred with bulls from other high-yielding cows.

Question 31

What technique has become widely available?

Answer 31

Since about 1950, the technique of artificial insemination has become widely available.

Question 32

What is artificial insemination?

Answer 32

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.

Question 33

How is artificial insemination used with bulls?

Answer 33

Bulls with many desirable features are kept and semen is obtained from them.

Question 34

What is done with the semen of bulls?

Answer 34

The semen is diluted, frozen and stored.

Question 35

Where does this semen then go?

Answer 35

Farmers can buy quantities of this semen to inseminate their cows.

Question 36

How is the farmer then able to inseminate their cows?

Answer 36

The semen is transferred into
the cow’s uterus using a syringe.

Question 37

What does artificial insemination allow us to do in terms of cows?

Answer 37

AI makes it possible for the semen from one prize bull to be used to fertilise many thousands of cows.

Question 38

What are certain farm animals (sheep and pigs) in terms of domestication?

Answer 38

Modern sheep are domesticated wild sheep, and pigs have been derived from wild boars.

Question 39

How are there many varieties of dogs that now exist?

Answer 39

All these have been derived from one ancestral type. This original ‘dog’ was a domesticated wolf.

Question 40

What is an image that shows how the many different breeds of dog all originate from a common ancestor - the wolf?

Answer 40

Question 41

What happened in domesticating the wolf?

Answer 41

Humans gained an animal that was
capable of herding stock animals.

Question 42

What is an example of how certain characteristics are able to be ‘bred out’?

Answer 42

The sheepdog has all the same instincts as the wolf except the instinct to kill. This has been selectively ‘bred out’.