Zoo/Bot 333
Genetics
Quiz 2
9/29/10
For answers to the quiz, please click here:
1. In radishes, color and shape are each controlled by a single locus with two
incompletely dominant genes. Color may be red (RR) purple (Rr) or white (rr) and shape
may be long (LL) oval (Ll) or round (ll). If two plants heterozygous for both loci are
crossed, what fraction of the progeny would be expected to be red and oval?
a) 1/16; b) 1/8; c) 3/16; d) 3/8; e) none of the above.
Questions 2-3 pertain to the following. If true-breeding green lentils are crossed to either
true-breeding tan or gray lentils, 3/4 of the F2 progeny are tan or gray depending on the
cross, and 1/4 of the progeny are green in both instances. In a cross of true-breeding tan
and gray lentils, all the F1 hybrids are brown. If F1 brown hybrids are crossed, four
different phenotypes appear among the F2 progeny, in a ratio of 9 brown: 3 tan: 3 gray : 1
green.
2. If F1 hybrid brown lentils were crossed to true-breeding gray lentils, what would be the
phenotypes and frequencies found among the progeny?
a) all brown; b) 1brown: 1 green; c) 3 brown: 1 gray; d) 3 brown: 1 green; e) none of the
above.
3. In an F1 hybrid cross between two brown lentils, the entire population of F2 progeny is
allowed to self-fertilize. What fraction of these F2’s will be able to produce progeny
representing all colors (i.e, brown, tan, gray and green F3 progeny)?
a) 1/16; b) 1/8; c) 1/4; d) 1/2; e) none of the above.
4. In mice, the Ay allele of the agouti gene is a recessive lethal allele, but dominant for
coat color (yellow). What phenotypes and ratios of offspring would you expect from the
cross of a mouse heterozygous at the agouti locus (genotype AAy) and also at the albino
locus (Cc) to an albino mouse (cc) heterozygous at the agouti locus (AAy)?
a) 3 agouti: 1 albino; b) 1 agouti: 2 yellow: 1 albino; c) 1 agouti: 1 yellow: 1 albino;
d) 3 albino: 2 yellow: 1 agouti; e) none of the above.
5. In class we discussed a situation in Drosophila, where two copies of a gene (i.e. a
recessive allele) at a specific gene locus (susu) was capable of suppressing the recessive
purploid (pupu) eye color phenotype. In a cross between heterozygotes for these two gene
loci, a ratio of 13 wild-type to 3 mutant was obtained. Suppose we had a situation where
a recessive allele was involved in the suppression of a dominant mutant phenotype. In a
cross between individuals heterozygous for this situation, what ratio of wild-type to
mutants would be expected?
a) 9 wild-type: 7 mutant; b) 9 mutant: 7 wild-type; c) 15 wild-type: 1 mutant; d) 13
mutant: 3 wild-type; e) none of the above.
Questions 6-8 pertain to the following:
In the tubular flowers of foxgloves, wild-type coloration is red, while a mutation called
white produces white flowers. Another mutation, called peloria, causes the flowers at the
apex of the stem to be huge. Yet another mutation, called dwarf, affects stem length. You
cross a white-flowered plant (otherwise wild-type) to a plant that is dwarf and peloria, but
has wild-type red flower color. All of the F1 plants are tall with white, normal-sized
flowers. You cross the F1 plant back to the dwarf parent, and see the progeny shown
below:
Dwarf, pelora
172
White
162
Dwarf, pelora, white
56
Wildtype
48
Dwarf, white
51
Pelora
43
Dwarf
6
Pelora, white
5
6. True or false: The allele governing white flower color is dominant.
7. The map distance between the white and pelora genes is most accurately measured as:
a) 18.8 m.u.; b) 19.1 m.u.; c) 19.7 m.u.; d) 21.2 m.u.; e) 21.8 m.u.
8. The coefficient of coincidence for the above cross is:
a) 0.121; b) 0.217; c) 0.402; d) 0.495; e) 0.678.
Questions 9 and 10 pertain to the following. There are two genes linked on the X
chromosome that are 10 map units apart, the Xg blood group locus and the steroid
sulfatase locus. Individuals that are Xg+ contain the Xg antigen on red blood cells, while
individuals that are Xg- lack the Xg antigen. Individuals that carry the Sts allele at the
steroid sulfatase locus have normal skin, while individuals homozygous or hemizygous
for the recessive sts allele have the disease ichtyosis, where the skin is very scaly. A
father with no Xg antigen and icthyosis has a normal daughter with Xg antigen.
9. If the child is a son, what is the probability he will lack antigen and have ichthyosis?
a) 5%; b) 10%; c) 25%, d) 50% e) none of the above.
10. If the child is a son, what is the probability that he would have both the antigen and
icthyosis?
a) 5%; b) 10%; c) 25%, d) 50% e) none of the above.