Today rest of his animals or plants. The

Today we are going to learn about species, breeds and
varieties.

Species

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A group of organisms which are able to produce offspring which
can also reproduce are called a species. Members of the same species have very
similar characteristics but there can also be some variation in these
characteristics.

Breeds

A group of animals may have special differences in their
inherited characteristics from the rest of their species. A group like this is
called a breed (e.g. different breeds of dog).

Why might selective breeding be useful to a farmer or a plant breeder?

 

Farmers and
plant breeders may choose or ‘select’ an animal or plant with certain
characteristics (e.g. good milk production in cows). They then use this animal
or plant to breed from as the characteristic it possesses is one the farmer or
breeder wants to see in the rest of his animals or plants. The offspring that
have the best of these characteristics are then bred from again. This process is
called selective breeding and is how many new breeds and varieties are created.

When two
different breeds or varieties are bred together to produce an offspring with
characteristics from both of the breeds or varieties, cross-breeding occurs.

 

Plant breeding

 

In nature,
pollen grains (the male gametes) are carried by the wind or insects to the
stigma of another flower. This is called pollination. Plant breeders transfer
the pollen that they want to the stigma that they choose, therefore keep the
characteristics they want.

 

Fertilisation
in a plant occurs when a pollen grain grows a tube down through the style until
it meets an ovule. It grows into the ovule and meets an egg cell. The nucleus
from the pollen grain goes into the egg cell and fuses with the egg cell
nucleus. Look at the diagram and see if you can see how this happens.

Many of the
characteristics that plant breeders choose are visible (e.g. fruit size, yield)
but some are not visible (e.g. making sure a plant is disease resistance).

Variation can be caused by the environment

 

Some
characteristics vary due to an organism’s surroundings (environment). For
example, plants growing in different areas of a field may be different heights
depending on the amount of light, water and mineral salts that they get. These
things are all physical environmental factors.

Make notes to describe the difference between cross breeding
and selective breeding.

Explain why both might be used by famers and plant breeders.