genetic variation
Genetic mutations involve structural, usually transmissible change in DNA or RNA within a cell or organism. Somatic mutations affect the cells of an organism, yet are not trasmitted to the next generation unless they affect the germline, those zygotes, such as ova and sperm that are committed to reproduction. Transmissible mutations affect the germline or result from errors during replication and cell division during reproduction.
Sequence mutations result from nucleotide substitutions, insertions, deletions, or re-arrangements of gene segments. On a larger scale, chromosomes are altered during replication and cell division by deletion, duplication, inversion, recombination, translocation, transposition, and non-disjunction.
Depending upon their effects upon an organism within a particular environment, mutations may be neutral, beneficial, or deleterious. The commonest mutations affect single nucleotides (point mutations or SNPs). Because the genetic code is redundant, many single nucleotide substitutions are neutral.
The genetic makeup of descendent diploid populations differs from that of the parental population by virtue of recombination, the random shuffling of genes during meiosis.
Insertion of mobile genetic elements, transposons and retrotransposons, increases genetic variability. The human genome, for example, includes approximately 500,000 Alu elements located within introns, and 25,000 of those could become new exons, coding for polypeptide sequences, by undergoing a single-point mutation.
As a result of alternative splicing, mutations that alter a splice site or a nearby regulatory sequence can have subtle effects by shifting the ratio of the resulting proteins without entirely eliminating any form. Alternative splicing also generates new polypeptide combinations from already existing code. Recently, researchers have demonstrated that modification of regulation of a single gene has enabled rapid phenotypic speciation in sticklebacks.
Alternative promoters enable mammals to extract more variability from fixed DNA sequences by regulating location and timing of transcription, adjusting the timing of protein production or generating alternative proteins by modifying the location at which transcription commences. Roughly 40-50 % of human and mouse genes have alternative promoters, which are more active during embryological development, and which display evolutionary conservation.
Statistical, population mechanisms operate upon allele frequencies within populations. Natural selection involves transmission of gene combinations that derived from parental genotypes that have proven favorable to survival and to reproductive success. Purely random bottleneck and randomly isolated founder effects are mechanisms of genetic drift, the random transmission of alleles between generations. Gene flow refers to the movement of genes from the gene pool of one population into that of another, brought about by movement of individual animals, gametes, or spores. Gene flow increases biodiversity and acts against speciation pressures by rendering two populations more similar to each other.
Sequence mutations result from nucleotide substitutions, insertions, deletions, or re-arrangements of gene segments. On a larger scale, chromosomes are altered during replication and cell division by deletion, duplication, inversion, recombination, translocation, transposition, and non-disjunction.
Depending upon their effects upon an organism within a particular environment, mutations may be neutral, beneficial, or deleterious. The commonest mutations affect single nucleotides (point mutations or SNPs). Because the genetic code is redundant, many single nucleotide substitutions are neutral.
The genetic makeup of descendent diploid populations differs from that of the parental population by virtue of recombination, the random shuffling of genes during meiosis.
Insertion of mobile genetic elements, transposons and retrotransposons, increases genetic variability. The human genome, for example, includes approximately 500,000 Alu elements located within introns, and 25,000 of those could become new exons, coding for polypeptide sequences, by undergoing a single-point mutation.
As a result of alternative splicing, mutations that alter a splice site or a nearby regulatory sequence can have subtle effects by shifting the ratio of the resulting proteins without entirely eliminating any form. Alternative splicing also generates new polypeptide combinations from already existing code. Recently, researchers have demonstrated that modification of regulation of a single gene has enabled rapid phenotypic speciation in sticklebacks.
Alternative promoters enable mammals to extract more variability from fixed DNA sequences by regulating location and timing of transcription, adjusting the timing of protein production or generating alternative proteins by modifying the location at which transcription commences. Roughly 40-50 % of human and mouse genes have alternative promoters, which are more active during embryological development, and which display evolutionary conservation.
Statistical, population mechanisms operate upon allele frequencies within populations. Natural selection involves transmission of gene combinations that derived from parental genotypes that have proven favorable to survival and to reproductive success. Purely random bottleneck and randomly isolated founder effects are mechanisms of genetic drift, the random transmission of alleles between generations. Gene flow refers to the movement of genes from the gene pool of one population into that of another, brought about by movement of individual animals, gametes, or spores. Gene flow increases biodiversity and acts against speciation pressures by rendering two populations more similar to each other.
Labels: alternative promoters, alternative splicing, conservation, deletions, duplication, genetic mutation, insertions, inversion, natural selection, recombination, substitutions
posted | 12/18/2007 07:03:00 PM
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