Fundamentals of Conservation Biology. Malcolm L. Hunter, Jr.. Читать онлайн. Newlib. NEWLIB.NET

Автор: Malcolm L. Hunter, Jr.
Издательство: John Wiley & Sons Limited
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Жанр произведения: Биология
Год издания: 0
isbn: 9781119144175
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of the differences between cows and horses as manifestations of genetic diversity because we can usually distinguish species readily without knowing anything about their genes. Species that are an exception to this generalization (i.e. genetically distinct but not obviously so to us) are called cryptic species (see Chapter 3).

      (Charles Smith/Flickr/CC BY 4.0)

Photo depicts two morphs of the eastern gray squirrel well known from the eastern United States.

      (James P. Gibbs, author)

      In sum, wherever there are two alleles for the same gene or, to state it more explicitly, different configurations of DNA occupying the same locus (gene) on a chromosome, genetic variation occurs within an individual and is also expressed as variation among individuals. This variation is the “grist” for biological evolution – without it evolution would grind to a halt. Ultimately the diversity of all life on the planet is rooted in how genetic differences among individuals are slowly shaped by evolution into different lineages and ultimately expressed as differences among populations, species, and eventually at higher taxonomic levels. For these reasons, differences in the distributions of alleles are the foundation of measuring genetic diversity. (For details on how genetic diversity arises through processes such as mutation and natural selection, see Hartl 2000; Frankham et al. 2009; Allendorf et al. 2013.)

      Measuring Genetic Diversity

      There are many methods to determine qualitative variation among individuals and populations in the types of alleles present at a given locus. An older but still used, indirect technique, called protein electrophoresis, involves extracting a “soup” of all the enzymes present when tissues of an individual (e.g. a leaf sample, skin clip) are crushed and their cell contents released. A sample of this soup is placed into a gel made of starch and water and subjected to an electrical field. Different alleles for particular genes produce different variations of enzymes called allozymes that move at different rates based on slight changes in their protein structure that alter their electrical charges. By probing the gel with dyes that express only when they encounter a particular allozyme, you can see with your own eyes genetic variation at the molecular level based on how slowly or quickly different proteins with different electrical charges move down the gel.

      Despite the promise of genomics, sequencing entire genomes is still quite laborious and costly. Therefore, until genomic analysis becomes more routine, a small sample of genes is still typically selected for measurement of genetic diversity and identity. We assume the pattern this subset of genes shows is reflective of the entire genome. Similarly, it is usually not possible to test all the individuals in a population; thus, a sample of individuals is used. After the allelic distribution for a sample of genes from a sample of individuals has been determined, an index to describe these distributions quantitatively can be calculated. Conservation biologists are most interested in indices of two important genetic properties of populations – polymorphism and heterogeneity – to quantify genetic diversity and guide conservation decision‐making.