Oct. 19, 1999                                    Test II       Biology 3250
                 (C)          !!!!Warning don't assume these questions will be
                                         on this years Midterm!!!!!!!
        30 Marks
       Part A.  Multiple Choice (1 point each): write the letter for the correct answer in the blank on the left.
____  1. With incomplete dominance, a likely ratio resulting from a monohybrid cross would be
    A.  3:3       B.  1:2:2:4       C.  1:2:1       D.  9:3:3:1       E.  3:1
____  2. Multiple alternative forms of a given gene are called
    A.  codominance   B.  alternation of generations   C.  multiple alleles   D.  incomplete dominance
                 E.  hemizygosity
____  3. One gene pair masks the expression of a non-allelic gene pair. This is called
    A.  codominance   B.  epistasis   C.  dominance  D.  pleiotropy   E.  additive alleles
____  4. Six gene pairs each have two additive alleles. How many genotypic classes are expected? _________

____  5. When two genes are unlinked the term normally applied is:
                 A.  discontinuous inheritance B.  continuous inheritance  C.  independent assortment D.  tetrad analysis
                 E.  dominance and/or recessiveness

____ 6. Hemizygosity would most likely be associated with which of the following?
              A. codominance     B. incomplete dominance  C. trihybrid   D. sex-linkage  E. sex-limited
____ 7.  A haploid fungus with 15 chromosomes mates and goes through meiosis. What is the total number of
               chromatids visible in each nucleus at the end of meiosis I? A. 10    B. 15     C. 20     D. 30      E. > 30
____  8. Gene A and gene B are linked. Gene A is 10 map units from the centromere. A test cross produces
              8 AaBb out of a total of 100. The estimated map distance between gene A and B is ____________.
____ 9.  Pseudodominance is associated with: A.epistasis  B.translocation C. inversion D. deletion  E. duplication
_____10. Down syndrome is caused by an extra copy of chromosome 21. This is an example of:
         A.  polyploidy  B.  euploidy  C.  aneuploidy  D.  triploidy  E.  monoploidy

_____11. Assume there are 12 map units between two loci in the mouse and that you are able to microscopically
               observe meiotic chromosomes in this organism. If you examined 200 primary oocytes, in how many
               would you expect to see a chiasma between the two loci mentioned above? _________.

          12. Many of the colour varieties of summer squash are determined by interacting genes. AA or Aa give
               white, aaBB or aaBb give yellow, and aabb produces green. A homozygous white is crossed to a green
               plant. The F1 is backcrossed to the green parent. Give the phenotypes and their ratio the progeny:

_____13. Assume that in the F2 generation of a series of crosses, 1/32 of the offspring resemble one parent or the
               other parent from the parent (P) generation. How many gene pairs are involved in producing these

_____14. On an autosome, genes A and B are 10 mu apart. On another autosome, genes C and D are 20 mu
                apart. An AABBCCDD male mates with an  aabbccdd female. What % of the gametes produced by
                their hybrid offspring will be ABCD? _____________.
_____15. The polyploidy condition which is formed from the addition of one extra set of chromosomes,
             identical to the normal haploid complement of the same species is known as:____________________.

Part B. Short answer (2 points each):

1. In corn, the genes for tassel length (alleles T and t) and rust resistance (alleles R and r) are known to be on separate chromosomes. In the course of making routine crosses, a breeder noticed that one TtRr plant gave unusual results in a testcross to the double recessive pollen parent. The results were: TtRr 98, ttrr 104, Ttrr 3,
ttRr 5. Explain these results as fully as possible.

2.  In yeast, the mating aBD  x   Abd gives following haploid spores: ABD=386 ABd = 35 Abd = 386
    AbD = 35 aBD = 386 aBd = 35 abd = 386 abD = 35. What can you conclude?

3. The alga Chlamydomonas produces unordered tetrads. The B locus is 3 m.u. from the centromere of chromosome 3 and the A locus is 18 m.u. from the centromere of chromosome 7. From the cross  A  +   x    +  B there is no crossing over between the B gene and its centromere, but in 12 % of the individual meioses there is a single crossover between the A gene and its centromere.  List the different types of unordered tetrads produced and the expected % of each.

  4.  Draw a translocation heterozygote during meiosis I and indicate how the chromosomes would separate to produce viable gametes.


5. A researcher crosses two pure-breeding white-flowered individuals from different populations of Antirrhinum. The F1 plants are all white flowered. When the F1 plants are self-pollinated to produce the F2 130 white and 30 red flowered progeny are produced. Explain the inheritance using gene symbols and give the genotype of the parents, F1 and F2.

Part C.  (5 points)

 In a certain diploid plant, the three loci A, B, and C are linked as follows:

       A_________B_____________C         A plant with genotype constitution  A b c / aBC is crossed
                                                                    with a plant of genotype a b c / a b c. Assuming 20 %
                20 mu                        30 mu         interference, what genotypic classes will be found and what
                                                                    will be their frequency in 1000 progeny?