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Gregor Mendel , through his work on pea plants , discovered the fundamental laws of inheritance (Sambamurty , 2005 . He deduced that genes come in pairs and are inherited as distinct units , one from each parent . Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits . Mendel 's Laws of Heredity are usually stated as : 1 ) The Law of Segregation 2 ) The Law of Independent 3 ) The Law of Dominance

Evolution is the process by which modern organisms have descended from ancient ancestors . Evolution only occurs when

there is a change in HYPERLINK "http /evolution .berkeley .edu /evolibrary /glossary /glossary_popup .php ?wo rd gene frequency " \t "gpop " gene frequency within a HYPERLINK "http /evolution .berkeley .edu /evolibrary /glossary /glossary_popup .php ?wo rd population " \t "gpop " population over time . These genetic differences are heritable and can be passed on to the next generation Evolutionary change can be because of any one of the following cause Mutation , migration , genetic drift and natural selection

A HYPERLINK "http /evolution .berkeley .edu /evolibrary /glossary /glossary_popup .php ?wo rd mutation " \t "gpop " mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration . That would make the genes for brown beetles more frequent in the population

Migration to a new environment may expose a population to new selective pressures and , as a consequence , favour the transmission of pre-existing variants that confer an advantage in the new conditions

In very small populations , rare alleles can become common or disappear because of genetic drift - random changes in gene frequency that are not due to selection , gene mutation , or immigration

Study of population genetics provided a basis whereby small differences in population variation have been shown to be able to drive the process of natural selection at a remarkably rapid pace . Natural selection by environment can be better understood by studying the Andes population in the high mountains where , their climate is cold . Consequently they have pasturage for their animals the year hypoxia , the decreased partial pressure of oxygen that occurs at higher elevations (Pawson and Jest 1978 . With increasing altitude , oxygen density decreases steadily so that at 3000 meters (10 ,000 ft , the partial pressure of oxygen is less than 70 of sea-level pressure . Above 5000 meters , oxygen pressure is sufficiently low that permanent human settlements cannot be maintained Oxygen plays a key role in physiological functioning across animals including cellular respiration and growth . Hence in absence of adequate oxygen levels this specific population 's adaptive feature of having large lungs has helped them survive the harsh natural conditions better than their neighborhood populations

Another example of genetic variation is concerned with the ability of adult humans to make use of the milk sugar lactose and with the role of cows and bulls in human societies . The enzyme lactase necessary for the digestion of this sugar is very high in young mammals and adults out grow their ability to digest this sugar because their lactase...

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