speciation /adaptive rad

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Stages of Speciation.

-1) initially members of the same species share the same gene pool and interbreed freely

2) then a population becomes split by a barrier (isolation mechanism)

This prevents the gene flow between populations it stops interbreeding between the two groups.

There are three types of barriers

-Geographical

-Reproductive( failed courtship behaviour, organisms become reproductive at different times of the year.)

-Ecological (changes in pH, Temperature)

3) random mutations occur, which is important as if these mutations are advantageous and help the species exploit their niche better the mutations will be passed on to their offspring.

4) Selection pressures acting on each sub popouation are different depending on the local conditions, e.g. predators , food availability, climate, disease

-alleles which make members of a sub population better at expolitng their environment will be passed on and spread among the sub population

5) The gene pools of these sub populatiobs are altered so drastically they become genetically distinct

If the barrier is removed

they are unable to interbred and produce fertile offspring

Thus speciation has occurred.

Adaptive Radiation

is the evolution of a group of related organisms from a common ancestor along different lines in response to an environmental change, by adapting over a loong period of time they are able to exploit wider environmental changes/ ecological niches

This promotes the optimum use of many different types of

environment by the various species that evolve and reduces competition between them.

Eg

of Adaptive Radiation

Darwin's Finches

When Charles Darwin visited the Galapagos

Islands (600 miles off the west coast of South America) he

observed many different types of finch not seen on the mainland. These finches possessed different beak size

and shape according to their diet. It is thought that these Galapagos island

finches once evolved from the mainland species of finch. The mainland finch had been blown by freak

weather conditions on to the islands (geographical barrier) In

the island environment freed from competition by other mainland species, the

finches diversified and adapted to occupy many different niches eventually

producing new species of finch.

Exntinction of a species

- as newer better species arise, those less suited and less adapted ot their environment are more likely to die- this can be due to environmental factors like climatic change or to do with mans activities, like overhunting and the destruction of habitats.

Many conservation techniques-

Captive Breeding- e.g, zoos

this is offsite protection

wildlife reserves- on site protection.

cell banks

Artifical Selection

selective breeding

breeders dilerately breed crops and domesticated animals with characteristics which are favourable to humans e.g. cattles have been selected to bred to produce offspring with a higher milk yield, or more meat.

(cabbage, broccoli, brussel sprouts have been bred from wild cabbage)

Hybridisation

occurs when two different types of pure bred (homozygous) parents of the same species are crossed

The heterozygous hyrbrid offspring are usually stronger, bigger, or more fertile than the other parent. This is called hybrid vigor

-the advantage of this is that favourable characteristics of both parents are expressed together in the offspring. the disadvanatge of this is that the hybridisation must be repeated wth the same parents every year.

e.g. AABBccdd x CCDDaabb

2desirable dominant features 2 different desirable

dominant characteristics

Genetic Engineering

is used to develop new varieties

It involves the transfer of genes from the genome of one organism, e.g. human to another organism e.g. bacterium.

In genetic enginerring it is important to be able to locate genes or groups of genes on chromosomes

this can be done:

1) gene probes short length of single stranded DNA

-comp. to the gene which is to be located

- has a radioactive label so it can be easily identified

2) recognition of banding patturns

once desired gene has been identified, two enzymes play an important role

-ligase - joins desired gene into plasmid, by sealing their sticky ends)

-endonuclease

leaves cuts

open plasmid and cut desired gene out of chromosome

hormones manufactured using this method

-insulin

-growth

somatic fusion

- this allows two different species who are sexually incompatible to breed successfully and produce a new species. Unspecialised cells of the two species are removed (not gametes)

This

process involves removing the

cell walls of the two species using the enzyme cellulase. The cell is now known as a protoplast.

The

protoplasts from the different plant species are now fused together to form a hybrid. Cell wall formation is then induced.

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