NATURAL SELECTIONSC.912.L.15.13

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NATURAL SELECTION

• WHAT YOU NEED TO KNOW• You need to know the conditions required for

natural selection to occur. These include: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success.

• You need to understand genetic drift and gene flow.

• You need to know how mutation and genetic recombination increase genetic variation.

• NATURAL SELECTION:

• The process by which forms of life having traits that better enable them to adapt to specific environmental pressures, as predators, changes in climate, or competition for food or mates, will tend to survive and reproduce in greater numbers than others of their kind, thus ensuring the perpetuation of those favorable traits in succeeding generations.

• Compare survival of the fittest.

• IndividualsIndividuals with favorablefavorable traitstraits are more likely to leave more offspring better suited for their environmentenvironment.

Natural Selection• CHARLES DARWIN (1809-1882)• Hired as Naturalist on H.M.S. Beagle• Sailed on Five Year Scientific Expedition

• Proposed Evolution Resulting from Natural Selection:– Organisms Produce Many Offspring– Competition for Food, Territory, Mates, etc.– Those With Best Traits Survive – Organisms Change Over Many Generations

• Time Frame: Millions of Years

OVERPRODUCTION OF OFFSPRING

• Overproduction of offspring: In any given generation, populations tend to create more progeny than can survive to reproductive age.

INHERITED VARIATION

• Variations of genomes between members of species, or between groups of species thriving in different parts of the world as a result of genetic mutation.

STRUGGLE TO SURVIVE

1. To remain alive or in existence.2. To carry on despite hardships or trauma; persevere: families

that were surviving in tents after the flood.3. To remain functional or usable.

REASONS:Not enough resources (food, water, shelter, mate, etc.)

DIFFERENTIAL REPRODUCTIVE SUCCESS

• When one group has more viable offspring than another. If two populations are similar but one has a variation that leads to fewer births and more deaths, you will see differential reproductive success between the populations.

GENETIC DRIFT• Genetic drift is a mechanism of evolution that

occurs by random chance rather than natural selection. In genetic drift, a population experiences a change in the frequency of a given allele, prompted by random luck rather than a need for adaptation. This differs from natural selection, in which allelic frequency is altered based on the fittest genes surviving to reproduce and the weaker genes dying off. Genetic drift tends to be a phenomenon amongst smaller populations, while natural selection holds sway in larger populations.

GENETIC DRIFT

GENE FLOW

• the alteration of the frequencies of alleles of particular genes in a population, resulting from interbreeding with organisms from another population having different frequencies.

GENE FLOW

GENETIC VARIATION• Without genetic variation, some of the basic mechanisms

of evolutionary change cannot operate.• There are three primary sources of genetic variation, which

we will learn more about:• Mutations are changes in the DNA. A single mutation can

have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations.

• Gene flow is any movement of genes from one population to another and is an important source of genetic variation.

• Sex can introduce new gene combinations into a population. This genetic shuffling is another important source of genetic variation.

• Genetic shuffling is a source of variation.

MUTATION A permanent, heritable change in the nucleotide

sequence in a gene or a chromosome; the process in which such a change occurs in a gene or in a chromosome.

GENETIC RECOMBINATION

• The process of forming new allelic combination in offspring by exchanges between genetic materials (as exchange of DNA sequences between DNA molecules).

Over time, the climate of an island became drier, which resulted in changes to the populations of various island finch species. Finch populations with a certain beak shape thrived, while those not having that beak shape decreased. Which of the following describes a necessary condition for these changes in the finch populations to occur?A. fewer mutations B. limited food resources C. limited beak variations D. overproduction of offspring

Which of these would have the least effect on natural selection in a subspecies of giraffes that is geographically isolated from other subspecies of giraffes? A. available nichesB. existing predatorsC. chromosome numberD. available food resources

Mutations within a DNA sequence areA. natural processes that produce genetic diversityB. natural processes that always affect the phenotypeC. unnatural processes that always affect the phenotypeD. unnatural processes that are harmful to genetic diversity

Which of the following best illustrates natural selection? A. An organism with favorable genetic variations will tend to survive and breed successfully. B. A population monopolizes all of the resources in its habitat, forcing other species to migrate.C. A community whose members work together utilizing all existing resources and migratory routes.D. The largest organisms in a species receive the only breeding opportunities.

A small population of chimpanzees lives in a habitat that undergoes no changes for a long period. How will genetic drift probably affect this population? A. It will accelerate the appearance of new traits.B. It will promote the survival of chimpanzees with beneficial traits.C. It will increase the number of alleles for specific traits.D. It will reduce genetic diversity.

A small portion of the population that is geographically isolated from the rest of the population runs the risk of decreased.A. genetic driftB. mutation rateC. natural selectionD. genetic variation

In his book On the Origin of the Species, Charles Darwin described how species change over time. Which of the following is NOT part of his observations that describes the mechanisms of natural selection? A. Organisms produce more offspring than can survive.B. Disease and natural disaster will limit population growth.C. Species today descended with modifications from ancestral species.D. Organisms with advantages will survive and reproduce.

Theodosius Dobzhansky discovered that successful species tend to have a wide variety of genes that do not appear to be useful to the species in its present environment. What did this discovery help explain about genetics and the changes that occur in a species over time? A. Environments with more organisms tend to have more successful species.B. Species with greater genetic diversity adapt more easily to changing environments.C. Changing environments prevent species from adapting and surviving.D. Species in a stable environment are more resistant to a changing environment.