errata 23921

modules/m66512/index.cnxml

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 <para id="fs-id2305474">The generation of genetic maps requires markers, just as a road map requires landmarks (such as rivers and mountains). Scientists based early genetic maps on using known genes as markers. Scientists now use more sophisticated markers, including those based on non-coding DNA, to compare individuals’ genomes in a population. Although individuals of a given species are genetically similar, they are not identical. Every individual has a unique set of traits. These minor differences in the genome between individuals in a population are useful for genetic mapping purposes. In general, a good genetic marker is a region on the chromosome that shows variability or polymorphism (multiple forms) in the population.</para>
 <para id="fs-id1446134">Some genetic markers that scientists use in generating genetic maps are <term id="term-00008">restriction fragment length polymorphisms</term> (RFLP), variable number of tandem repeats (VNTRs), <term id="term-00009">microsatellite polymorphisms</term>, and the <term id="term-00010">single nucleotide polymorphisms</term> (SNPs). We can detect RFLPs (sometimes pronounced “rif-lips”) when the DNA of an individual is cut with a restriction endonuclease that recognizes specific sequences in the DNA to generate a series of DNA fragments, which we can then analyze using gel electrophoresis. Every individual’s DNA will give rise to a unique pattern of bands when cut with a particular set of restriction endonucleases. Scientists sometimes refer to this as an individual’s DNA “fingerprint.” Certain chromosome regions that are subject to polymorphism will lead to generating the unique banding pattern. VNTRs are repeated sets of nucleotides present in DNA’s non-coding regions. Non-coding, or “junk,” DNA has no known biological function; however, research shows that much of this DNA is actually transcribed. While its function is uncertain, it is certainly active, and it may be involved in regulating coding genes. The number of repeats may vary in a population’s individual organisms. Microsatellite polymorphisms are similar to VNTRs, but the repeat unit is very small. SNPs are variations in a single nucleotide.</para>
-<para id="fs-id1794075">Because genetic maps rely completely on the natural process of recombination, natural increases or decreases in the recombination level given genome area affects mapping. Some parts of the genome are recombination hotspots; whereas, others do not show a propensity for recombination. For this reason, it is important to look at mapping information developed by multiple methods.</para>
+<para id="fs-id1794075">Because genetic maps rely completely on the natural process of recombination, natural increases or decreases in the recombination level of a given genome area affects mapping. Some parts of the genome are recombination hotspots; whereas, others do not show a propensity for recombination. For this reason, it is important to look at mapping information developed by multiple methods.</para>
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 <section id="fs-id2474128">
 <title>Physical Maps</title>