Any population of an organism which lacks variety
in its gene pool is particularly susceptible to various factors.
This is the case
e.g. climate change - change in weather
patterns
attack by a pathogen - bacteria, fungus or
virus
If any of one these factors affect a population,
in a varied gene pool, not all of the population will die.
Those individuals with the right set of genes will
survive.
The survivors will be able to reproduce and pass
on the advantageous genes.
These days new crop varieties in agriculture are
bred for disease resistance - lost or poor crop yields costs money!
Increased yields of better quality food crops is a
worthy economic goal.
Horticulturalists - plant breeders, are also
interested in quality flowers, fruit or vegetables for garden
cultivation.
The 'ideal aims' for crops i.e. beneficial
characteristics of the variety are:
Plants that grow and mature quickly with good
crop yields.
Crops that have a long shelf-life and store
well (e.g. flowers), or can be frozen (e.g. vegetables.
Vegetables that have a distinctive taste,
looks and texture.
Flowers that are attractive to look at e.g. in
colour, have a pleasing aroma-scent, perhaps larger and bigger
than their wild origins!
However, its a good idea to preserve wild
versions of plants we cultivate and use their wide-ranging gene pool
for future breeding programmes.
In order to achieve these aims you need to:
Selectively breed a variety in large numbers
of identical plants to give the greatest possibility of being able
to select the plants with desired characteristics i.e. those listed
above.
BUT, there is the danger of having crops that
are genetically too uniform - as already discussed (at the start), a
narrow gene pool is susceptible various things.
In traditional plant breeding, a plant with
desirable characteristics is crossed with another plant with the same or
another desirable characteristic.
The plants are chosen from a mixed population or
existing varieties.
Pollen is transferred from the flowers of one
plant to the flowers of another to fertilise it.
To ensure the desired breeding direction - that is
to concentrate the gene pool of desired traits, you must stop the
plants from self-pollinating each other and also avoid cross-pollinating
with a different plant variety.
From the new plant seeds the process is repeated
over several generations.
Need some examples - pictures