) Explain how natural selction may bring about changes in a population and what conditions may be necessary to bri about speciation

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a)} How may Variation Arise in Natural populations

b) Explain how natural selction may bring about changes in a

population and what conditions may be necessary to bri about


A species is a group of organisms that look alike and can reproduce

successfully to produce fertile offspring. Within a species there is

variation which can be caused my meiosis, random fertilisation,

mutations and the natural environment. Genetic variation increases the

chance for survival of a population if the environment changes. For

example the introduction of a new virus in to the new environment may

kill some organisms but others may be resistant to it and survive. If

all the organisms had been genetically identical they may have all

been killed. The species that survive are likely to live longer and

pass on their useful genes to future generations. The change in a

species over time is called evolution. There are two types of

variation; continuous and discontinuous variation. Discontinuous

variation is when there is a complete range of measurements from one

extreme to the other for a normal characteristic, such as human

height. Discontinuous variation is where characteristics are fit into

separate categories with no intermediates such as human blood groups.

During the process of meiosis each homologous pair of chromosomes

aligns independently along the equator and whether the maternal or

paternal chromosome faces a particular pole is quite random. This is

known as independent assortment and is one of the causes of variation

in the gametes. Unlinked genes are transmitted independently of each

other, leading to random distribution of genes...

... middle of paper ... that particular environment. A species may be well-adapted to its

environment, but if the environment changes, then the species must

adapt or die. In either case the original species will become extinct.

Since all environments change eventually, it is the fate of all

species to become extinct (including our own). Reproductive Isolation

(Sympatric Speciation) Reproductive Isolation is a type of genetic

isolation. Here the formation of a new species can take place in the

same geographical area, e.g. mutations may result in reproductive

incompatibility. A new gene producing, say, a hormone, may lead an

animal to be rejected from the mainstream group, but breeding may be

possible within its own groups of variants. When this mechanism

results in the production of a new species it is known as sympatric

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