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Variations of Mendelian Genetics

  1. In short horn cattle, a red bull (RR) is crossed with a white cow (rr). The offspring are roan, intermingled red and white hairs.
    1. What do we call this variation of Mendelian genetics?
    2. How would a rancher maintain a herd of roan cattle?
  2. The coat color in cattle1 is described by the following genetic characteristics:
    • The gene for black (Rb) is dominant to the gene for red (R).
    • The gene for black (Rb) and the gene for white (r) are codominant. Therefore, an individual with one gene for black and one gene for white will be black-roan (intermingled black and white hairs).
    • The gene for red (R) and the gene for white (r) are also codominant, producing the red-roan when these two genes are present.
    • An individual with two genes for white (r) will be white.

    Describe the monohybrid cross using a Punnett square AND give the phenotypic ratio for these crosses:

    1. A homozygous black cow with a homozygous red bull.
    2. A homozygous black cow with a homozygous white bull.
    3. A homozygous red cow with a homozygous white bull.
  3. The storage roots of radishes may be long, round or oval. Using the data below from a series of experiments, show how root shape is inherited in radishes.
    • Crosses between long and oval produced 159 long and 156 oval.
    • Crosses between round and oval produced 199 round and 203 oval.
    • Crosses between long and round produced 576 oval.
    • Crosses between oval and oval produced 121 long, 243 oval and 156 round.


1. "Color Pattern Inheritance in Beef Cattle. Dr. Stanley R. McPeake. University of Arkansas Cooperative Extension Service. 2002. FSA3067-PD-6-01N. Online. http://www.uaex.edu"