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Mendelian Genetics Practice Problems

1. What is a chromatid?

2. How many chromatids are present in humans during metaphase II?

3. Do map units (m.u.) equal the physical distance between two genes? Are they similar?

4. The l allele on the X - chromosome is recessive lethal and located 20 m.u. from the w allele for eye     color. (w=white eyes w+=red eyes). If a female fly (w+ l/w l+) is crossed with a wild type male fly.        What percentage of sons will die? What percentage of living sons will have white eyes?








5. a------------------b------------c
          7.5mu             5.5mu

How many double crossovers would you expect to see in 1,000 progeny?

If you observed 2 double crossovers what is the interference?

6. R=round r=wrinkled
    G=yellow g=green

     If a round yellow plant is testcrossed and produces a 1:1:1:1 phenotypic ratio, what genotype is          the round yellow parent?







7. Two genes code for pigment in mouse fur (A and B). Albino mice are aabb. Any other genotype           yields gray mice. The A and B genes recombine 20% of the time. If two mice are crossed (Ab/aB x       Ab/aB):

    What percent of gametes will be ab?

    What percentage of offspring will be white?


8. True breeding red and white flowers are crossed to yield all pink flowers in the F1.

    The pink flowers are an example of ___________________________?

    What will the F2 look like?





9. Complementation test of mice that have white fur: The goal is to determine how many genes are         involved in fur color.

      1 2 3 4 5 6 7
    1 - - + + + - +
    2 - + + + - +
    3 - + - + -
    4 - + + +
    5 - + -
    6 - +
    7 -


    How many genes affect white fur in mice?

10. Female flies (c+ y v/c y+ v+) yielded 1,000 gametes.

      c+ y   v   331
      c   y+ v+ 349
      c   y   v+ 93
      c   y+ v   54
      c+ y   v+ 66
      c+ y+ v   97
      c+ y+ v+ 6
      c   y   v   4

     Identify parental types, single crossover types, and double crossover types.

     Which gene is in the middle?

     Find the recombination frequencies for each of the genes.


     Draw the genetic map.  


11. When does genetic recombination (crossing over) occur in the cell cycle?

12. If an organism is 2n, what number of chromosomes are present after these stages of meiosis?

      Metaphase I:

      Prophase II:

      Telophase II:

13. What is the given hypothesis for chi-square tests in this course?

14. R=round r=wrinkled
     G=yellow g=green

     In a cross of RrGr x rrgg, the following offspring are produced. Use the chi-square test to evaluate        whether the data follow Mendel's laws.

     Class Observed Expected
      RrGg 55 ?
      Rrgg 51 ?
      rrGg 49 ?
      rrgg 52 ?



15. Some individuals with a mutant gene have a normal phenotype. What is this phenomenon called?

16. Some individuals with a mutant gene can be much more affected than others with the same                 genotype. What is this phenomenon called?

17. In a di-hybrid cross, anything that changes the 9:3:3:1 ratio is called ________________?

     What does this mean about the two genes involved?

18. Three strains of bacteria grow on complete media. None grow on minimal media. Strain #1 grows        on media with ornithine, strains #1 and #2 grow on media with citrulline, strains #1, #2, and #3 all      grow on media with arginine.

     Draw the biosynthetic pathway and label the mutations each strain has.