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When farmers are planning to plant a field of vegetables, they want a crop that will grow well and

produce a high yield so that they get more vegetables for their money. The farmers also want a cropthat can withstand very cold temperatures over the winter or very high temperatures and drought

over the summer. They will want plants that are resistant to disease and pests. Most of all, they willwant a crop that looks and tastes good so people will want to buy it.

For over 10000 years farmers have saved the seeds from successful crops to produce the netyear!s crop. They didn!t realise it then but they were selecting useful genes.

Today, plant breeders choose plants that they know have good characteristics. They have developedsimple yet effective techni"ues for cross#pollination $the transfer of pollen from the anther of one

plant to the stigma of another plant%.First of all the breeder must decide which plant is to produce the pollen and which will receive the

pollen on its stigma. These must be clearly marked, perhaps with different coloured thread or a tag.The net step is to ensure that the plant is not fertilised by its own pollen $self#pollination%. &ome

plant breeders remove the anthers $the male parts, which produce pollen%. To prevent cross#

pollination $pollination by pollen from another flower% breeders tie up the petals of the flower with apiece of string or put a polythene bag over the flower to protect the stigma.

To cross#pollinate, the anther is removed from one plant and placed in a container using twee'ers.

The protector, e.g. polythene bag, is removed from the flower of the other plant. The anther is thentaken out of the container using twee'ers and is rubbed gently over the stigma of the other plant sopollen is left on it. The protector is then replaced so the plant is not pollinated by unwanted pollen.

(lternatively, a paintbrush can be used to brush pollen onto the stigma.

)*

9Ad(6) Breeding plants 2

1 Make a list of all the

characteristics a plant breeder may

look for in+

a red rose bushes

b potato plantsc tomato plants.

2 Write a list of instructions for

cross#pollinating plants for someone

who has not done this before.

3 ow do breeders make sure that

plants don!t pollinate themselves-

4 ow do breeders make sure

unwanted pollen doesn!t pollinate the

plants-

5 a lant breeders can increase the

numbers of a particular plant variety

"uickly by cloning. /ive an eample of

how this might be done.

bloning does not produce new

varieties. Why not-

6 &ome plant breeders use genetic

modification to get the varieties that they

want. plain why this method is "uicker

than selective breeding at producing new

varieties with the right characteristics.

I CAN... describe how plants are selectively breddescribe how plants are cross#pollinated

consider the benefits of cloning and genetic modification.