Evolution

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Evolution

Evolution is the changes in orgnisms over generations

as a result of genomic variations.

Gene

transfer

1. Vertical - Genes are transferred from parents down to their

offspring.

This can happen by:

ð Sexual reproduction

-

This

involves 2 parents who differ from one another genetically.

-

Offspring

inherit different combinations of genes from each other.

ð Asexual

reproduction

-

Is

reproduction from a single parent. Produces offspring who are

geneticallyidentical to the parent.

2. Horisontal transfer of genetic

material (prokaryotes).

In prokaryotes (who reproduce using asexual reproduction) – genetic material can be transferred

from one cell to another through horizontal gene transfer

Natural

selection

-

is the non-random increase in frequency of

DNA sequences that increase survival.

Organisms produce more offspring

than the environment can support

A struggle for existence

occurs and many offspring die before they can reproduce

Only those who are better adapted

to the environment (the fittest) will survive and bred and pass those adaptations

on to their offspring.

This process is repeated generation

after generation causing gradual change in the

characteristics of a species.

Sexual

selection

-

is an increase in successful reproduction.

Genetic drift

The random increase and decrease in frequency of

sequences, particularly in small populations, as a result of neutral mutations

and founder effects.

1.

Neutral mutations

These change the

nucleotide sequence of a gene, but do not change the amino acids coded for. They

are not subject to natural selection, but are affected by genetic drift.

2.

Founder effect

If a population

becomes isolated and is not large enough to contain the entire gene pool, gene

frequencies will be different in that population.

An example of the

founder effect can be seen in the different blood group allele frequencies in

different human populations.

Speciation

Is the formation of a new biological species. It is

brought about by evolutionary change.

A species is a

group of organisms capable of interbreeding and producing fertile offspring,

and which does not normally breed with other groups.

There are 2 types of speciation:

1.

Allopatric speciation

This

occurs when gene flow between 2 (or more) populations is prevented by a geographical barrier.

e.g.

rivers, mountain ranges, desert, sea

2.

Sympatric speciation

2

(or more) populations live in close proximity in the same environment but still

become genetically isolated.

This

happens due to a behavioural or ecological barrier or by the occurrence of polyploidy (in plants only).

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