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Introduction to Genetics

Genetics is the study of how living organisms transfer biological information from one generation to the next, i.e., how particular characteristics are inherited. Initially, genetic information was gathered by analyzing inheritance patterns; sexually reproducing organisms with particular sets of easily observable characteristics were allowed to mate (crossed) and the characteristics of the resulting progeny (offsping) were noted. By performing thousands of such crosses and by very carefully analyzing the resulting data, a general outline for the genetic systems of sexually reproducing eukaryotic organisms was elucidated. This body of information is generally referred to as classical or Mendelian genetics, honoring the father of modern genetics, Gregor Mendel. Molecular genetics, on the other hand, attempts to elucidate the precise chemical basis of heredity and the specific mechanisms of genetic control.

In this laboratory you will be introduced to an extinct animal known as a glyptodont (a relative to today's armadillo). You have access to genetic material/information from four families of glyptodonts, all found by paleontologists in a remote cave. Using breeding experiments which are the tools of classical genetics as well as chromatography, electrophoresis, two of the tools of molecular genetics, you will attempt to learn what you can about the inheritance of shell color in these organisms.

This laboratory module assumes that you have a working knowledge of terms used in modern genetics. Although this is not an exhaustive list (see the glossary), you must be familiar with the following terms:

Gene In Mendelian genetics, a unit of inheritance. In molecular genetics, a sequence of nucleotides in DNA that code for specific protein or RNA molecules.

Allele An alternative form of a gene. Different alleles for a gene are responsible for different phenotypic expressions of a particular trait. For example, three alleles control human blood type; which two of these allels any individual possesses determines that person's blood type.

Dominant Allele An allele that, when present, is always expressed, i.e. its expression is observable in the organism's phenotype. By convention, dominant alleles are designated by a capital letter (A, B, T, etc.).

Recessive Allele An allele that is only expressed when the organism is homozygous (see below) for this allele. By convention, recessive alleles are designated by the lower-case version of the letter chosen to designate the dominate allele for a particular trait (a,b,t, etc.)

Phenotype The genetically controlled trait(s) exhibited by an organism. A particular phenotype may be easily observable with the naked eye (e.g. pea plant height), or observable only using tools such as microscopes, or chemical tests (e.g. blood type).

Genotype The entire complement of genes (alleles) possessed by an organism. In many cases, this term is used to refer to the particular alleles controlling a specific genetic trait.

Homozygous The case where an organism possesses two identical alleles for the same trait.

Heterozygous The case where an organism possesses two different alleles for the same trait.

These terms, as well as the shorthand notation for designating alleles, will be used thoughout this module, so be sure to familiarize yourself with their definitions and usage.

To begin, select an exercise from the links in the navigation bar on the left. You may choose any of the exercises listed, but it is suggested that you perform the introductory exercise, Phenotypes, first. In the Chromatography and Electrophoresis exercises that follow, you will be able to investigate the molecular/biochemical basis for the inherited phenotype of shell color. Finally, in Genotypes you can use classical breeding experiments to confirm the genetic basis of shell color.

To download and print a worksheet for this exercise, select Resources from the navigation bar to the left.

To begin, select Phenotype from the links in the navigation bar on the left.