Genetics 311, Practice problem set 3.

1) Label the meiotic stage represented in each of the following diagrams of cells from the germ line of an individual with one pair of acrocentric and one pair of metacentric chromosomes.
      Anaphase I        Anaphase II        Metaphase I          Prophase I          Telophase II

2) The pedigree below shows the incidence of the X-linked disease hemophilia A in a small family.  If individual II2 marries a normal man, what's the chance that her first child will have hemophilia?
  Answer: 1/8

3) Locus A and locus B are 16 m.u. apart.  An AAbb individual was mated to an aaBB, and the F1 testcrossed.  What fraction of the F2 progeny are expected to show the phenotype Ab?
Answer: 42%

4) Two homozygous maize plants were crossed and produced all normal F1.  When the F1 were testcrossed, progeny phenotypes appeared as follows:

       60     virescent                                        4      sterile, virescent
     170     virescent, glossy                         180     sterile
         7     glossy                                           62     sterile, glossy
     270     sterile, virescent, glossy               235     wild type

Are all three of these genes linked? Test using chi-square.

Answer: Locus g and locus s are linked, chi-square = 74.4
               Locus g and locus v are linked, chi-square = 529
               Locus v and locus s are not linked, chi-square = 4.3

I didn't ask, but in case you're curious, the map distances are:

                CofC = 0.226

5) Owing to the small size of chromosome four in Drosophila, monosomics and trisomics are viable but tetrasomics and nullisomics are not.  The chromosome #4 gene, bent bristles (b),  is completely recessive.  What phenotypic ratio would you expect from the cross of two trisomic wildtype flies carrying the bent gene,  Bbb x Bbb?

19 wildtype : 8 bent bristles

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