Grayda, Rolando Bse Bs1 2

8/3/2019 Grayda, Rolando Bse Bs1 2

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THE MICROEVOLUTION

TOUR .


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The Hardy-Weinberg Law

It was discovered independently by Godfrey Hardyand Wilhelm Weinberg in 1908..

It states that the frequencies of genes in an ideal

population remain constant and their proportions stay

the same unless certain evolutionary forces affect thepopulation..

These evolutionary forces include: Mutation; Geneflow; Genetic drift; Nonrandom mating or SexuialSelection;and Natural Selection which will be

discussed shortly after this..


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Agents of Evolution

Click on any of the following topics for

discussion.

Mutation

Gene Flow

Genetic Drift

Nonrandom Mating or Sexual Selection


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Mutation

It refers to the alteration in the chemicalcomponent of the gene. This alteration isinheritable since it occurs in the gene level

These are the origin of all new genes andthe utmost source of genetic variation and soit permits alteration of the gene pool.


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The most common source of mutation isRadiation.

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Gene Flow

It refers to the movement of alleles from one populationto the other. This movement causes alteration of the allelefrequencies present in a gene pool.

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Immigration is the movement from a gene pool. This is the removal ofcertain alleles from the gene pool.

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Emigration is the movement toward a gene pool. It is the addition of newalleles to the population.

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Genetic Drift..

It refers to change in allele frequencies by randomchance.

Or Random Drift

The effect of chance events are generallynegligible. On the other hand, with a smallpopulation, the effect may have a considerableimpact.

Special Cases of Genetic Drift:BottleneckFounder Effect

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Bottleneck refers to a drastic reduction in size of alarge population due to a catastrophe or otherunfavorable conditions (famine, disease, tsunami,meteor collision, etc.).

In a bottleneck event, some alleles may becompletely wiped out from a population. Here, thegenotypes of the survivors will, be the source of thesubsequent generations.

For example, the northern Elephant seal, hunted

almost to extinction, have a very uniform gene poolbecause of the 20 surviving seals in 1890; just onemale fathered all the offspring.

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In the Founder effect, a small number of individuals migrate to an area isolated from the originalpopulation. The gene pool of the new populationmay vary significantly from the original population

since all the alleles will be coming from themigrants which initiated the new population.

Here, some alleles may be temporarily removed

from the gene pool but these may be reintroducedthrough migration.

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Nonrandom Mating or Sexual Selection

In nature, the individuals in general, are particularof their mates. This increases the occurrence ofalleles with favorable characteristics.

Types include:

Assortative Matingindividuals of a

specific phenotype may seekmates of a similar phenotype.Ex. Humans tend to marrysomeone with whom theyshare to some extent suchtraits as stature, age, or evenhair color, etc.

Inbreedingthis is a special case of

assortative mating which can alterthe gene pool. Continued inbreedinginclines to homozygosity. Potentiallyharmful recessive alleles (ex.Huntingtons disease) will exert their

harmful effect on the offspring whoinherit one from both parents. Inother words, continued inbreedingincreases the chance of producing

offsprings with defective genes.

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Natural Selection

A type of selection wherein naturechooses which population subgroup is themost fit..

Patterns of Natural Selection

1. Stabilizing2. Directional3. Disruptive

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Stabilizing Selection

Individuals with intermediate phenotypeswill be the most likely to survive,

Ex. Neonates which have an averagebirthweight will be the most likely to suvive.

POPULATION

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PENOTYPE

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Directional Selectionindividuals with the most

favorable phenotypes are the most

common. Directional selection is usuallyobserved in a population subjected to newenvironmental condition.

Ex. The population of Melanic form ofBiston betularia increased over the

peppered form due to the industrialrevolution.

POPULATION

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PENOTYPE

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Disruptive Selectionextreme phenotypes are favored

over intermediate phenotypes

Ex. Suppose there are snails with brown,spotted brown-white,and white variants. Ifthe snails were brought to rocky areas,brown variants will most likely to survivebecause it has the most favorablephenotype for camouflage. Same with

white sand, white snails will subsist.Neither of both conditions the spotted nailswill survive.

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PULATION

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PENOTYPE

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Grayda, Rolando Bse Bs1 2