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7: Linkage and Mapping

  • Page ID
    4092
  • As we learned in Chapter 6, Mendel reported that the pairs of loci he observed behaved independently of each other; for example, the segregation of seed color alleles was independent from the segregation of alleles for seed shape. This observation was the basis for his Second Law (Independent Assortment), and contributed greatly to our understanding of heredity. However, further research showed that Mendel’s Second Law did not apply to every pair of genes that could be studied. In fact, we now know that alleles of loci that are located close together on the same chromosome tend to be inherited together. This phenomenon is called linkage, and is a major exception to Mendel’s Second Law of Independent Assortment. Researchers use linkage to determine the location of genes along chromosomes in a process called genetic mapping. The concept of gene linkage is important to the natural processes of heredity and evolution.

    Figure 7.1: Linkage affects the frequency at which some combinations of traits are observed. (Wikipedia-Abiyoyo-CC:AN)

    • 7.1: Linkage
      Mendel’s Second Law does not apply to every pair of genes that could be studied. In fact, we now know that alleles of loci that are located close together on the same chromosome tend to be inherited together. This phenomenon is called linkage, and is a major exception to Mendel’s Second Law of Independent Assortment. Researchers use linkage to determine the location of genes along chromosomes in a process called genetic mapping and is important to natural processes of heredity and evolution.
    • 7.2: Recombination
      In heredity, recombination is any process that results in gametes with combinations of alleles that were not present in the gametes of a previous generation. Interchromosomal recombination occurs either through independent assortment of alleles whose loci are on different chromosomes. Intrachromosomal recombination occurs through crossovers between loci on the same chromosomes . In both cases, recombination is a process that occurs during meiosis (mitotic recombination is relatively rare).
    • 7.3: Linkage Reduces Recombination Frequency
    • 7.4: Crossovers Allow Recombination of Linked Loci
    • 7.5: Inferring Recombination From Genetic Data
    • 7.6: Genetic Mapping
      Because the frequency of recombination between two loci (up to 50%) is roughly proportional to the chromosomal distance between them, we can use recombination frequencies to produce genetic maps of all the loci along a chromosome and ultimately in the whole genome.
    • 7.7: Mapping With Three-Point Crosses
    • 7.E: Linkage and Mapping (Exercises)
    • 7.S: Linkage and Mapping (Summary)

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