Examples of phenotypic variation in the following topics:
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- Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population.
- Because natural selection acts directly only on phenotypes, more genetic variation within a population usually enables more phenotypic variation.
- Some species display geographic variation as well as variation within a population.
- An enormous amount of phenotypic variation exists in the shells of Donax varabilis, otherwise known as the coquina mollusc.
- This phenotypic variation is due at least partly to genetic variation within the coquina population.
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- Genes are not the only players involved in determining population variation.
- Phenotypes are also influenced by other factors, such as the environment.
- 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.
- This graph shows geographical variation in moose; body mass increase positively with latitude.
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- If natural selection favors an average phenotype by selecting against extreme variation, the population will undergo stabilizing selection.
- When the environment changes, populations will often undergo directional selection, which selects for phenotypes at one end of the spectrum of existing variation.
- Sometimes natural selection can select for two or more distinct phenotypes that each have their advantages.
- In these cases, the intermediate phenotypes are often less fit than their extreme counterparts.
- Different types of natural selection can impact the distribution of phenotypes within a population.In (a) stabilizing selection, an average phenotype is favored.In (b) directional selection, a change in the environment shifts the spectrum of phenotypes observed.In (c) diversifying selection, two or more extreme phenotypes are selected for, while the average phenotype is selected against.
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- The observable traits expressed by an organism are referred to as its phenotype and its underlying genetic makeup is called its genotype.
- The observable traits expressed by an organism are referred to as its phenotype.
- Johann Gregor Mendel's (1822–1884) hybridization experiments demonstrate the difference between phenotype and genotype.
- That is, the hybrid offspring were phenotypically identical to the true-breeding parent with violet flowers.
- A trait is defined as a variation in the physical appearance of a heritable characteristic.
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- However, the heterozygote phenotype occasionally does appear to be intermediate between the two parents.
- A variation on incomplete dominance is codominance, in which both alleles for the same characteristic are simultaneously expressed in the heterozygote.
- The chinchilla phenotype, cchcch, is expressed as black-tipped white fur.
- The Himalayan phenotype, chch, has black fur on the extremities and white fur elsewhere.
- Finally, the albino, or "colorless" phenotype, cc, is expressed as white fur.
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- Many mutations will have no effect on the fitness of the phenotype; these are called neutral mutations.
- A mutation may produce a phenotype with a beneficial effect on fitness.
- The evolution of species has resulted in enormous variation in form and function.
- In other cases, similar phenotypes evolve independently in distantly-related species.
- Explain why only heritable variation can be acted upon by natural selection
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- Natural selection cannot create novel, perfect species because it only selects on existing variations in a population.
- Natural selection can only select on existing variation in the population; it cannot create anything from scratch.
- Natural selection is also limited because it acts on the phenotypes of individuals, not alleles.
- Natural selection acts on the net effect of these alleles and corresponding fitness of the phenotype.
- It is simply the sum of various forces and their influence on the genetic and phenotypic variance of a population.
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- A population's genetic variation changes as individuals migrate into or out of a population and when mutations introduce new alleles.
- 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.
- The appearance of new mutations is the most common way to introduce novel genotypic and phenotypic variance.
- 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.
- This mutation has introduce a new allele into the population that increases genetic variation and may be passed on to the next generation.
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- An individual may carry a very beneficial genotype with a resulting phenotype that, for example, increases the ability to reproduce (fecundity), but if that same individual also carries an allele that results in a fatal childhood disease, that fecundity phenotype will not be passed on to the next generation because the individual will not live to reach reproductive age.
- As natural selection influences the allele frequencies in a population, individuals can either become more or less genetically similar and the phenotypes displayed can become more similar or more disparate.
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- Genetic diversity refers to any variation in the nucleotides, genes, chromosomes, or whole genomes of organisms.
- Nucleotide variation is measured for discrete sections of the chromosomes, called genes.
- Within any single organism, there may be variation between the two (or more) alleles for each gene.
- However, a greater total number of genes might not correspond with a greater observable complexity in the anatomy and physiology of the organism (i.e. greater phenotypic complexity).
- Describe how variations in the size and number of genes can arise through evolutionary mechanisms