Lab 5

Ribonucleic Acids (RNA)

A second class of nucleic acids known as RNA are very similar to DNA, but with some important differences. RNA, as opposed to DNA, is single rather than double stranded, is considerably shorter in overall length, and contains the nucleotide Uracil (U) instead of Thymine.

Mutations

Changes to the DNA sequence are the ultimate source of all genetic variation. Most mutations that occur within a gene have negative consequences for the organism.

Base Pairing

DNA is "self-complimentary" in that A only pairs with T, while C only pairs with G. This simple principle of base pairing allows for "copying" of the DNA sequence by pairing nucleotides together to form new strands

Alleles

For each gene, there are many possible alleles, which are alternate forms of a gene.

Heterozygosity

Having a genotype with one of each allele, helps explain how recessive disease alleles can be maintained in a population.

Deoxyribonucleic Acid (DNA)

Is a molecule found in nucleus of nearly every cell in your body. DNASE has two opposing strands that coil around one another to form a "double helix," and it is composed of four basic building blocks known as nucleotides.

Natural Selection

Is perhaps the most familiar force of evolutionary change. First proposed by Darwin in his "Origin of Species", natural selection occurs as the result of non-random, differential survival and reproduction of some individuals in a variable population. When there is variation in a population, individuals whose genetic "makeup" make them more likely to survive, reproduce, and pass their genes to the next generation within a give environment are favored by natural selection. As a result, their traits tend to become more numerous in the population over time. Note that emphasis here is not on survival alone, but survival and reproduction of inherited traits. Natural selection can act to remove some alleles from the population over time while allowing other alleles to persist and become increasingly common. If the selection is strong enough and/or the trait is advantageous enough, the genes may increase to 100% frequency in the population, or become "fixed". If a trait is outcompeted by another more advantageous trait, and it is lost from the population, it is said to have become "extinct". However, in order for natural selection to occur, there must be heritable differences among the individuals of a population. If there is no genetic basis for a trait (i.e. musical preference, culture, etc.), it cannot evolve by natural selection. Finally, if all individuals are genetically identical (no variation), the same genes will be passed on to the next generation and evolution by natural selection cannot occur. Thus, natural selection cannot act unless there is genetic variation in a population.

Summary

Of the evolutionary forces discussed here, the random forces are mutation and genetic drift, while the non-random forces are natural selection and gene flow. With subdivided populations, the occurrence of random mutations, the differences in natural selection between differing environments, and genetic drift may act to make populations more genetically distinct from one another over time. Conversely, gene flow between different populations will act to make the populations more genetically similar to one another. Evolution occurs via four primary mechanisms - natural selection, mutation, genetic drift, and gene flow. Mutation is the ultimate source of all variation. Natural selections shapes this genetic variation by eliminating or increasing the abundance of genes in a given environmental context. Gene flow acts to redistribute genetic variants among different populations. Finally, like most natural phenomena, other random factors may also have a substantial effect. Random changes in allele frequency within a population occur by genetic drift. Remember - although individuals are subject to natural selection, the population is the unit of evolutionary change. As a result, populations are continuously evolving over time, but individuals never evolve.

Transcription

RNA is made by "copying" the DNA through simple base pairing in process known as transcription.

Genotype

Species differ in their genetic makeup.

Phenotype

Species differ in their observable trait.

Gene flow

The fourth and final force of evolution is the non-random influence of gene flow. Gene flow refers to the movement of alleles between populations through both migration and interbreeding of individuals from different populations. This migration and interbreeding can alter the frequency of alleles within a population, can add variation caused by mutation to be spread to new populations, and serves to homogenize populations, making them more similar to each other over time. Conversely, genetic isolation caused by physical or reproductive barriers, or through differences in natural selection acting on a population, are all examples of situations that can impede gene flow. If a population becomes genetically isolated from one another, the various influences of the evolutionary forces discussed here may lead to significant changes in allele frequencies between the populations, resulting in a divergence of the populations into two or more distinct species through a process known as speciation.

Chromosomes

The genome is packaged into chromosomes, or highly condensed and tightly bundled sections of DNA that can fit inside a cell nucleus.

Anthropological Genetics

The goal of anthropological genetics is to understand the evolutionary relationships, demographic histories, and genetic bases of biological variation in humans and non-human primates.

Translation

The resulting information in the newly made RNA molecule, known as "messenger RNA" (mRNA), is used to make a new protein in a process called translation.

Genes

The sections of the DNA which carry information for making a protein are known as genes.

Genome

The sum total of all DNA sequences in an individual is known as the genome

Evolution

The term evolution is common,y used to refer to any inheritable change in a species that occur over a long period of time. The accumulation of these heritable changes over time may lead to the emergence of new traits or even the generation of whole new species. More precisely defined, however, evolution can be most simply understood as a change in allele frequencies in a population over time.

Forces of Evolution

There are four different forces that can lead to evolutionary change over time. These are: natural selection, mutation, gene flow, and genetic drift. Natural selection and gene flow are non-random forces, while mutation and genetic drift occur randomly.

Nucleotides

These nucleotides are Adenine (A), Thymine (T), Guanine (G), and Cytosine (C), and different combinations of these four nucleotides form the basis of genetic information.

Central Dogma of Biology

This overall process of going from DNA to RNA to Proteins is how information coded in DNA sequences gives rise to a functional protein product or trait, and it is known as the Central Dogma of Biology.

Genetic drift

is another means of random change in allele frequencies within a population that is produced by the random factors of inheritance and population subdivision. This process is particularly powerful when a small group of individuals splits off from a larger population to found a new population. As the new founder group is a random sample of the original group's genetic variation, there may be differences in the overall proportions of certain alleles due to the phenomenon of sampling error (errors that occur when a sample does not represent the actual group). A particular allele which was rare in the parent population may have been randomly chosen more often than would be expected in the founder population, and thus, would be present at a higher than expected frequency in the new founder group. Thus, the resulting collection of alleles in the next generation of the founder population is more likely to resemble the founding population rather than the original population. This random cause of evolutionary change is a particular kind of genetic drift known as the founder effect. Another example of drift may occur if the number of individuals within a single population is suddenly and dramatically reduced, as in a natural disaster. The surviving remnant population may thus be genetically bottlenecked, resulting in a subsequent generation whose allele frequency differs from that of the parent generation. Bottlenecking can lead to reduced genetic variability in a population by randomly removing individuals from a population. In the absence of founder effects and genetic bottlenecks, genetic drift may occur through the random segregation and assortment of alleles that happens during gamete formation and fertilization. Since each parent has two alleles, and can only pass on one of them, there is a 50% chance per generation that an allele will not being passed on to an offspring. In a population as a whole, rare alleles are easily lost due to genetic drift, because there are not many of them in the population and not many chances that they will be inherited. Conversely, alleles that are common in a population are not as easily lost because there are more chances that they will be inherited. The chance of an allele being lost is also related to the population size. The bigger a population is, the lower the chance of an allele being lost, even when it is rare. The smaller a population is, the more likely that an allele can be lost. Thus, population size is inversely related to the influence of drift.

Mutation

or random changes in the DNA sequence, alters existing genes or creates new genes and is therefore the ultimate source of new genetic variation in any population. Because mutations may alter the frequency of alleles within a population (by introducing new ones), mutation is a second mechanism by which evolution can occur. Naturally occurring mutation rates are relatively low in humans and non-human primates, and most mutations either have no visible effect on phenotype (i.e., they are said to be "neutral"), or have a harmful effect on the organism (i.e., they are said to be "deleterious"). However, rarely, a mutation may occur which has an advantageous effect in a given environmental context. Natural selection is highly effective at spreading these new mutations through the population.