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10: Molecular Markers and Quantitative Traits

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    Fig10.1.png Figure \(\PageIndex{1}\): Many traits, such as body mass, show continuous variation, rather than discrete variation. Although environment obviously also affects this trait, some of the variation observed between individuals is heritable, and is dependent on the interactions of multiple alleles at multiple loci. The study of quantitative traits is one of many applications of molecular markers. (Flickr-Jamie Golombek-CC:AND)  
    • 10.1: Some Variations in the Genome Affect Complex Traits
      The genomic sequences of almost any two unrelated people differ at millions of nucleotide positions. Some of these differences would be found in the regions of genes that code for proteins. Others might affect the amount of transcript that is made for a particular gene. A person’s health, appearance, behavior, and other characteristics depend in part on these polymorphisms.
    • 10.2: Origins of Molecular Polymorphisms
      Some of mutations occur during DNA replication processes, resulting in an insertion, deletion, or substitution of one or a few nucleotides. Larger mutations can be caused by mobile genetic elements such as transposons, which are inserted more or less randomly into chromosomal DNA, sometimes occurring in clusters.
    • 10.3: Classification and Detection of Molecular Markers
      Mutations that do not affect the function of protein sequences or gene expression are likely to persist in a population as polymorphisms, since there will be no selection either in favor or against them (i.e. they are neutral). Note that the although the rate of spontaneous mutation in natural populations is sufficiently high so as to generate millions of polymorphisms that accumulate over thousands of generations, the rate of mutation is slow.
    • 10.4: Applications of Molecular Markers
      Several characteristics of molecular markers make them useful to geneticists.  DNA polymorphisms are a natural part of most genomes.  Geneticists discover these polymorphisms in various ways, including comparison of random DNA sequence fragments from several individuals in a population.  Once molecular markers have been identified, they can be used in many ways.
    • 10.5: Quantitative Trait Locus (QTL) Analysis
      We can use molecular markers to identify at least some of the genes (those with a major influence) that affect a given quantitative trait.  This is essentially an extension of the mapping techniques we have already considered for discrete traits.
    • 10.E: Molecular Markers and Quantitative Traits (Exercises)
    • 10.S: Molecular Markers and Quantitative Traits (Summary)

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