Some Practice Questions (from undergraduate days). These are just meant as suggestions to guide you to the kinds of problems you should be able to cope with.
Another suggested problem and review book: Schaum's Outline series, Theory and Problems of Genetics (3rd ed). McGraw-Hill, 1991.
1. How many gametes can be formed by an organism with the genotype AABbCcDdEe?
2. A coin is flipped and comes up heads. What is the probability that the next flip will yield heads? What about the third and fourth flips?
3. A plant heterozygous for four independently assorting genes (AaBbCcDd) is self fertilized. Determine the expected frequency of the following genotypes in the progeny: aabbccdd, aabbCcDd, AaBbCcDd, AABBCCdd. Assuming incomplete dominance, how many different phenotypes will be present in the progeny?
4. How many chromatids and centromeres per cell will a diploid organisms with a haploid number of 26 have at the end of (a) metaphase I; (b) metaphase II; (c) telophase I; (d) telophase II and (e) mitosis?
5. A cross is carried out between AB/aB and ab/ab. The following progeny and numbers of each are produced: AaBb (215); aabb (209); Aabb (36); aaBb (39). Which progeny are recombinants and what is the recombination frequency between A and B?
6. A three factor cross ABD/abd a abd/abd is carried out which yields the recombinant gamete AbD which is formed at a much higher frequency than Abd, What is the gene order?
7. An A/a heterokaryon is formed in Neurospora and the resulting asci are studied. If no crossing over occurs between the centromere and the gene, what is the arrangement of the spores in the ascus and is this a first or a second division segregation pattern?
8. If a single cross over occurs between the gene and the centromere in Neurospora, why is the spore pattern called a second-division segregation pattern (why does segregation not occur in the first division?)
9. If AB/ab heterokaryons are formed in Neurospora, why are the nonparental ditypes asci so infrequent compared with parental ditypes? How is the frequency of tetratype asci compared to that of nonparental ditype asci?
10. Establishing a map
Consider three linked genes in corn: +/b; +/lg; +/v. A testcross is made between a triple heterozygote and a homozygous recessive. The following progeny were observed:
165 + v lg 37 + + lg
125 b + + 33 b v +
64 b + lg 11 + + +
56 + v + 9 b v lg
A. What is the genetic composition of the heterozygote?
B. What is the gene order?
C. Calculate the coefficient of coincidence
HINTS
A. Determine which classes are the most frequent (non-recombinants). This will tell you what the heterozygote was.
B. Determine the order by comparing the DCO classes to the parental classes. Only one order will work here
Calculate the recombination frequency by adding all the recombinations between each of the loci.
Draw a map based on the recombination frequencies
C. Coefficient of coincidence (CC) = observed DCO ÷ expected DCO
BE ABLE TO DO THIS PROBLEM IN REVERSE ORDER, I.E. PREDICT THE FREQUENCIES WHEN THE DISTANCES ARE KNOWN
11. Example: A triple heterozygous female fly +/sc; +/ec; +/vg is crossed to a triply heterozygous recessive male (assume all mutant traits are recessive). The progeny are:
sc ec vg 233 sc + vg 12 Total = 1000
+ + + 239 + ec + 14
sc ec + 241 sc + + 14
+ + vg 231 + ec vg 16
Explain these results by drawing a suitable map
Hint: The presence of 4 equally frequent majority classes and 4 equally frequent minority classes suggests that two genes are linked and one gene is not
1. You expect a ratio of 1:1:1:1:1:1:1:1 is the three genes are unlinked. From the data, some of the genes must be linked. If all three genes were linked, you would observe only 2 majority classes
Second hint: set up the cross again looking at only 2 genes at a time
12. Given the following gene-gene distances, determine a map that includes all genes
O-R 3 R-A 13 R-G 5
M-R 7 G-A 8 O-G 8
M-G 12 G-N 10 O-N 18
Hint: Start with genes that have the largest distances between them since they must be near the ends.
18
O--------------------------------------------------N
8 G 10