Zoo/Bot 3333
Genetics
Quiz 2
10/2/09
For answers to the quiz, click here
The accompanying pedigree shows a very unusual inheritance pattern that actually did exist. All progeny
are shown, but the fathers in each mating have been omitted to draw attention to the pattern.
1. Which of the following is the most likely explanation of this data?
a) A Y-linked lethal; b) An autosomal dominant with sex-limited inheritance; c) an X-linked recessive; d)
an X-linked dominant; e) none of the above is likely.
The data set below was taken from a real human population, where many families were tested for the
ability to taste the chemical phenylthilcarbamide (PTC). These matings were grouped into three classes and
the progeny were totaled with the following results:
Parents
1) Taster x taster
2) Taster x nontaster
3) Nontaster x nontaster
Number of families
425
289
86
Children
Tasters Non-Tasters
929
130
483
278
5
218
2. Assuming the taster phenotype is dominant and the nontaster is recessive, which of the following is true?
a) The first data set should show a 3:1 ratio of taster:nontaster; b) the second data set should a 1:1 ratio of
taster:nontaster; c) the taster children in data set three are probably the result of mutation to the dominant
phenotype; d) all of the above; e) none of the above.
3. Which experiment was a direct demonstration that crossing over results in the physical breaking and
rejoining of chromosomes?
a) The work of Nettie Stevens; b) the work of Morgan and Sturtevant; b) the work of Creighton and
McClintock; d) the work of Curt Stern; e) two of the above are correct.
Questions 4-5 pertain to the
following: On the planet Riza, the
“luminescent horgon” is a flower
that has many color variations.
Crosses between several varieties of
the plant yield (chart at right):
Parents
orange x blue
purple x blue
purple x orange
orange x tan
tan x blue
F1 phenotypes
All orange
All purple
All sienna
All orange
All purple
F2 phenotypes
203 orange, 67 blue
152 purple, 52 blue
86 sienna, 41 orange, 43 purple
130 orange, 60 tan, 44 blue
181 purple, 79 tan, 60 blue
4. The color variations observed here indicate that:
a) the sienna allele is dominant to the purple allele ; b) two gene loci are involved; c) this cross is an
example of complementary gene action; d) all of the above; e) none of the above.
5. If the blue F2 offspring from cross 4 are crossed to a true-breeding orange strain, what will be the ratio
of progeny?
a) all orange; b) 1 orange: 1 blue; c) 3 orange: 1 blue; d) all sienna; e) none of the above.
Questions 6-7 pertain to the following cross. A fly heterozygous for
three different genes (AaBbCc) is testcrossed to a fly homozygous
recessive for these three mutations. The following progeny types are
produced (chart at right):
6. The distance between the a and b genes is:
a) 8.05 map units; b) 14.2 map units; c) 15 map units; d) 15.3 map
units; e) 16.1 map units.
Phenotype
+bc
a+c
abc
++c
a++
ab+
+++
+b+
Number of progeny
436
91
6
92
440
87
8
98
7. True or false. Only about 1.1% of the expected double crossovers are observed in this cross.
Questions 8-9 pertain to the following cross. A fly heterozygous for
three different genes (AaBbCc) is testcrossed to a fly homozygous
recessive for these three mutations. The following progeny types are
produced (chart at right):
8. True or false. The a and c genes are in the trans phasing
configuration in the heterozygous parent.
9. The above data set indicates that the c gene is:
a) unlinked to the a gene; b) linked to the b gene; c) 3.9 map units
from the b gene; d) all of the above; e) none of the above.
Phenotype
+bc
a+c
abc
++c
a++
ab+
+++
+b+
Number of progeny
228
19
20
234
231
227
21
20
10. The following asci were obtained in Neurosopora when a wild type strain (td+) was crossed to a
mutant strain unable to grow in the absence of tryptophan (td-).
Spore pair
Ascus type
1-2
td+
tdtdtdtd+
3-4
td+
td+
tdtd+
td5-6
tdtd+
td+
tdtd7-8
tdtdtd+
td+
td+
total
53
7
47
8
5
The distance between the td locus and the centromere is:
a) 5.4 map units; b) 8.3 map units; c) 10.8 map units; d) 16.6 map units; e) none of the above.