Genetic Variation in Populations

The Field of Biology that Studies Microevolution

Micro VS. MacroMicroevolution

Takes place over a short amount of time

Results in new characteristic

Within a population

Macroevolution Takes place over a long

amount of time Results in new species New populations created

Gene PoolsMade up of all the genes and

characteristics in one population

Population GeneticsPopulations and Gene Pools

Genetic Variation

The Hardy-Weinberg Model

Microevoltuion in Large Populations

Micro Evolution in Small Populations

Quantitative Traits

No two organisms are exactly alike.

Variations is what allows populations to adapt to new environmental conditions.

Populations and Gene PoolsMicroevolution-change within a species

Macroevolution-change over large periods of time, new species evolves

Population Genetics-field of study involving microevolution

Gene Pool-all of the genes of a local populations of organisms

Genetic VariationMany variations even within a species.

When two or more alleles of a gene for a trait are present in the gene pool, the population is said to be polymorphic.

Typically 0.5% is the largest amount of variation in a species.

Human Genetic Variation

The Hardy-Weinberg Model•The Hardy-Weinberg Model is a mathematical model used to predict gene pools.•The model was created by Godfrey H. Hardy to the left and Wilhelm Weinberg to the right in 1908.•Within the Hardy-Weinberg Model several assumptions are made these are..•The organism is diploid•Generations are non-overlapping•Population size is very large•Mutation is negligible•Reproduction is sexual •Gametes are random•Migration is negligible•Natural Selection does not occur.

These conditions almost never occur in the wild making the model inaccurate.

•Above is a table showing how The Hardy-Weinberg really works.

•The Union is the alleles of the two parents. The p and the q under the Frequency is the frequency of each allele. A is p and a is q. If the offspring is going to be homozygous then the letter is squared. If it is heterozygous the two numbers are multiplied together.

•The Hardy-Weinberg model only offers predictions because the circumstances need do not often occur. Also there are disturbances like genetic drift which alter the gene pool for no apparent reason.

MicroevolutionMicroevolution in large populations in large populations

Mechanisms that affect the gene pool:

Mechanisms that affect the gene pool:

Natural selection (increased reproductive success=increased allele frequency)

Genetic drift (random changes in small populations)

Gene flow (migration of individuals between populations)

Mutation (direct conversion of one allele to another)

Natural selection (increased reproductive success=increased allele frequency)

Genetic drift (random changes in small populations)

Gene flow (migration of individuals between populations)

Mutation (direct conversion of one allele to another)

Examples of Natural selection

Examples of Natural selection

Sickle-cell polymorphismEnglish peppered moth

Sickle-cell polymorphismEnglish peppered moth

Microevolution in Small Populations

• Small populations are subject to genetic drift.– Substantial effect!

• Founder Effect– Genetic drift that influences

new populations

• Possibility of inbreeding– Populations bottleneck

• Also from outside factors

• Inbreeding depression– Fertility and survival are

reduced in comparison to other populations that are not inbred

By Lizzie Tonkin

• Quantitative Traits are traits that can be measured on a scale, they are not either or. Ex: Skin color, size, and life span• Quantitative traits are controlled by multiple genes. These genes are called Quantitative Trait Loci (QTLs).

• Twins are used to study whether some traits are controlled by genes or the environment. • Identical twins have the same genomes, so quantitative traits can be measured. • If the environment is more important than genes for a trait, fraternal twins will be more similar; If genes are more important, the identical twins will be.• Some scientists think that intelligence is a genetic factor, but others think the studies have not been sufficient.

• QTL mapping is a way to find genes that control QTLs• Geneticists breed two line of animals, one at each end of the spectrum of the QTL they are mapping.

Ex: Age in fruit flies• A sequence of nucleotides is found near suspected places where a gene might be. The sequence should be something recognizable by enzymes.• The lines are then crossed, and the the offspring are crossed with each other• After many generations, the life span of the flies is analyzed. The one with the longest life probably has a gene for long life.• The fly’s genome is analyzed, and if it has any of the markers, the life gene is known to be near there.

• “Six Things Everyone should know about Genetics.” Photo. May 14 2010. <http://www.ashg.org/education/everyone_2.shtml>.

• “Life cultural.” Photo. May 14 2010. <http://i.livescience.com/images/about_you_skin_color.jpg>.

• “Twin Studies.” Photo. May15 2010. http://www.sciencemuseum .org.uk/on-line/genes/images/1-3-4-2-2-2-0-0-0-0-0.jpg

Citations

• http://upload.wikimedia.org/wikipedia/commons/7/7a/Populations.png