Why variations are important to understand

Some of the variations may provide an advantage to the organism to lead a successful life while other variations may not provide such adaptive advantage. Variations are inherited, as these are genetically controlled.

Hence a better adapted organism would transfer the favourable variation to its offspring; longer survival means more number of progeny. As a result each new generation of organisms would have the favourable variations in an increased proportion. Change in allele frequency within a gene pool over a time period is defined as microevolution. As we say that favourable variations in the gene pool would become more numerous with time, obviously alleles controlling such characteristics would increase in percentage in each generation.

Open survey. In: Facts In the Cell. Individuals of a species have similar characteristics but they are rarely identical, the difference between them is called variation.

Genetic variation is a result of subtle differences in our DNA. On average they occur once in every bases and are often found in the DNA between genes. Genetic variation results in different forms, or alleles , of genes. For example, if we look at eye colour, people with blue eyes have one allele of the gene for eye colour, whereas people with brown eyes will have a different allele of the gene.

Eye colour, skin tone and face shape are all determined by our genes so any variation that occurs will be due to the genes inherited from our parents. In contrast, although weight is partly influenced by our genetics , it is strongly influenced by our environment. For example, how much we eat and how often we exercise. Gene flow : Gene flow can occur when an individual travels from one geographic location to another.

Maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups. Gene flow strongly acts against speciation, by recombining the gene pools of the groups, and thus, repairing the developing differences in genetic variation that would have led to full speciation and creation of daughter species. For example, if a species of grass grows on both sides of a highway, pollen is likely to be transported from one side to the other and vice versa.

If this pollen is able to fertilize the plant where it ends up and produce viable offspring, then the alleles in the pollen have effectively linked the population on one side of the highway with the other. Species evolve because of the accumulation of mutations that occur over time. The appearance of new mutations is the most common way to introduce novel genotypic and phenotypic variance. Some mutations are unfavorable or harmful and are quickly eliminated from the population by natural selection.

Others are beneficial and will spread through the population. Whether or not a mutation is beneficial or harmful is determined by whether it helps an organism survive to sexual maturity and reproduce. Some mutations have no effect on an organism and can linger, unaffected by natural selection, in the genome while others can have a dramatic effect on a gene and the resulting phenotype. Mutation in a garden rose : A mutation has caused this garden moss rose to produce flowers of different colors.

This mutation has introduce a new allele into the population that increases genetic variation and may be passed on to the next generation. Population structure can be altered by nonrandom mating the preference of certain individuals for mates as well as the environment.

Explain how environmental variance and nonrandom mating can change gene frequencies in a population. If individuals nonrandomly mate with other individuals in the population, i. There are many reasons nonrandom mating occurs. One reason is simple mate choice or sexual selection; for example, female peahens may prefer peacocks with bigger, brighter tails.

Traits that lead to more matings for an individual lead to more offspring and through natural selection, eventually lead to a higher frequency of that trait in the population. Assortative mating in the American Robin : The American Robin may practice assortative mating on plumage color, a melanin based trait, and mate with other robins who have the most similar shade of color.

However, there may also be some sexual selection for more vibrant plumage which indicates health and reproductive performance. Another cause of nonrandom mating is physical location. This is especially true in large populations spread over large geographic distances where not all individuals will have equal access to one another.

Some might be miles apart through woods or over rough terrain, while others might live immediately nearby. Genes are not the only players involved in determining population variation. Phenotypes are also influenced by other factors, such as the environment. A beachgoer is likely to have darker skin than a city dweller, for example, due to regular exposure to the sun, an environmental factor.

Some major characteristics, such as gender, are determined by the environment for some species. For example, some turtles and other reptiles have temperature-dependent sex determination TSD.

TSD means that individuals develop into males if their eggs are incubated within a certain temperature range, or females at a different temperature range.

Temperature-dependent sex determination : The sex of the American alligator Alligator mississippiensis is determined by the temperature at which the eggs are incubated.

Eggs incubated at 30 degrees C produce females, and eggs incubated at 33 degrees C produce males. Geographic separation between populations can lead to differences in the phenotypic variation between those populations. Such geographical variation is seen between most populations and can be significant. As a result, the tree-colored moths are more likely to survive, reproduce, and pass on their genes. This process is called natural selection , and it is the main force that drives evolution.

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