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15.S: Molecular Markers and Quantitative Traits (Summary)
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Natural variations in the length or identity of DNA sequences occur at millions of locations throughout most genomes.
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DNA polymorphisms are often neutral, but because of linkage may be used as molecular markers to identify regions of genomes that contain genes of interest.
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Molecular markers are useful because of their neutrality, co-dominance, density, allele frequencies, ease of detection, and expression in all tissues.
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Molecular markers can be used for any application in which the identity of two DNA samples is to be compared, or when a particular region of a chromosome is to be correlated with inheritance of a trait.
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Many important traits show continuous, rather than discrete variation.These are also called quantitative traits.
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Many quantitative traits are influenced by a combination of environment and genetics.
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The heritable component of quantitative traits can best be studied under controlled conditions, with pure-breeding parents that are polymorphic for both a quantitative trait and a large number of molecular markers.
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Molecular markers can be identified for which specific alleles are tightly correlated with the quantitative value of a particular phenotype.The genes that are linked to these markers can be identified through subsequent research.