BioSc 231
General Genetics
Exam 3
Name __________________________________
Multiple Choice. (2 points each)
_____ The maximum recombination frequency between two genes is
A. 100%
B. 80%
C. 50%
D. 10%
E. 1%
_____ The linkage phase (cis or trans) of alleles in multiply heterozygous parents is detectable as the
A. Most frequent type of gametes in a three factor test cross.
B. Lowest incidence of crossing over
C. Largest number of map units between corresponding alleles
D. Highest frequency of recombination
_____ Which of the following statements is true about the heterozygous parent in the following cross?
An organism heterozygous for three genes AaBbCc was mated to a homozygote aabbcc, resulting in the progeny distribution below.
ABC
aBC
AbC
Abc
abC
aBc
Abc
abc
327
44
30
3
4
45
28
319
----800
A. Both chromosomes contain all dominant alleles
B. Both chromosomes contain all recessive alleles.
C. All the dominant alleles are located on one chromosome, and all the recessive alleles are located on the other homologous
chromosome.
D. Two of the dominant alleles are located on one chromosome and the other dominant allele is located on the other chromosome.
_____ A true breeding green cucumber with curled leaves is crossed with a true breeding yellow cucumber with flat leaves to produce
an F1 that is green with flat leaves. You perform a test cross to determine linkage with a cucumber that is yellow with curled leaves.
In this cross, which of the following describes all the recombinant phenotypes for the testcross progeny?
A. green, flat leaf AND green, curled leaf
B. yellow, flat leaf AND yellow, curled leaf
C. green, flat leaf AND yellow, curled leaf
D. green, curled leaf AND yellow, flat leaf
_____ Testcross data showed a 1:1 ratio of parentals to recombinants for the genes rv and x and the genes rv and h, and 5:1 ratio of
parentals to recombinants for the x and h genes, which of the following is correct?
A. The rv, x, and h genes are all located on the same chromosome.
B. The rv and x genes are located on one chromosome, and the h gene is located on a different chromosome.
C. The rv and h genes are located on one chromosome, and the x gene is located on a different chromosome.
D. The h and x genes are located on one chromosome, and the rv gene is located on a different chromosome.
E. The rv, x, and h genes are all located on different chromosomes.
_____ Which of the following statements is true?
A. When three linked genes are mapped, offspring derived from double crossovers always occur less frequently than offspring
derived from any of the single crossovers.
B. When three linked genes are mapped, offspring derived from double crossovers always occur more frequently than offspring
derived from any of the single crossovers.
C. When three linked genes are mapped, offspring derived from double crossovers always occur with the same frequency as offspring
derived from any of the single crossovers.
D. None of the above.
_____ Two genes with a 50% recombination frequency are
A. Present on homologous chromosomes.
B. In the cis configuration.
C. Present on a single chromosome.
D. On a separate chromosomes.
_____ The following three genes are located on a single chromosome in the order bd – ch – a. Genes bd and ch are 20 map units
apart, and genes ch and a are 17 map units apart. What is the probability of a double crossover in these regions?
A. 1.3%
B. 2.3%
C. 3.4%
D. 4.5%
E. 5.6%
_____ In unordered tetrad analysis, the tetratype pattern of segregation shows
A. Two genotypes with parental alleles
B. Two genotypes with nonparental alleles
C. One genotype with all parental alleles
D. All four possible allele combinations
_____ The ratio of the observed double crossovers divided by the expected number of double crossovers is the
A. Coefficient of coincidence
B. Coefficient of selection
C. Coefficient of coupling
D. Frequency of recombination
_____ In a cross of two mouse strains of phenotypes B D X b d the progeny were
42 B D
46 b d
5Bd
7bD
The frequency of recombination is
A. 11%
B. 12%
C. 24%
D. 50%
_____ Out of 800 progeny of a three-point testcross there were 27 double crossover recombinants, whereas 30 had been expected on
the basis of no interference. The interference is
A. 0.05
B. 0.10
C. 0.20
D. 0.80
E. 0.90
Problems (Pts).
(6) The following tomato plant traits were studied in a three point test cross. Normal (round) fruit or ovate
(long) fruit, flat leaves or curled leaves and solid color or mottled coloration. F1 plants (heterozygous for all
three genes) have normal fruit, flat leaves and solid coloration. F1 plants are crossed with a strain that has ovate
fruit, curled leaves and mottled coloration and the following offspring were obtained:
Normal, flat solid
304
Ovate, flat, solid
5
Normal, curled, solid
26
Ovate, curled, solid
60
Normal, flat, mottled
68
Ovate, flat, mottled
24
Normal, curled, mottled
3
Ovate, curled, mottled
310
What is the gene order?
What are the map distances between the middle gene and each of the two outer genes?
(4) Two-point testcrosses revealed the following map results:
ba___________pc 5.4 map units
pc___________v 8.9 map units
Draw the two possible maps for these loci.
What cross would resolve the two possible maps and what are the possible outcomes of that cross?
(5) The ferocious jackalope (see photo at right) is a popular research subject.
An experiment was performed to study the inheritance pattern of two important
traits: sharp pointy teeth vs. short dull teeth and long antlers vs short antlers. F1
fully heterozygous jackalopes were crossed and the following offspring were
generated:
47 sharp, long
18 sharp, short
13 dull, long
2 dull, short
What is the null hypothesis that is likely to fit the observed phenotypic ratios?
Use Chi-square analysis to determine if you should accept or reject the null hypothesis. (show all your work)
(6) In a dihybrid cross, you observe 308, purple flowered, tall, 110 purple flowered, short, 98 white flowered,
tall, and 44 white flowered, short F2 plants. Analyze these data using the chi-square test to see if
(a) they fit a 9:3:3:1 ratio
(b) the purple:white traits fit a 3:1 ratio
(c) the tall:short traits fit a 3:1 ratio
(4) An experiment to determine the inheritance of flower color in snap dragons crossed two plants with pink
flowers (li x li). The following progeny were recovered from the cross. 102 plants had red flowers (ll), 190 had
pink flowers (li) and 108 had white flowers (ii). Use a Chi-square test to determine whether those numbers fit a
Mendelian pattern of inheritance.
(6) The map distances between the following genes (e, g, h, o, p, r) were determined by a series of two point test
crosses. Draw a linear map of all the genes with the appropriate map distances.
g – h = 12 mu
h – r = 7 mu
g – r = 19 mu
p – h = 7 mu
p – r = 14 mu
o – h = 9 mu
o – e – 15 mu
g – o = 3 mu
e–h=6
(5) A fully heterozygous F1 goldfish with normal gold scales and fancy fins is crossed with one that has white
and gold scales and short fins. The following progeny are produced:
85 gold, fancy
90 gold and white, short
87 gold, short
88 gold and white, fancy
A. What is the recombination frequency?
B. Are these genes linked?
5 point bonus question
A cross was made between an aaeeRR plant and an AAEErr plant. The resulting F1 plants were testcrossed and
1000 offspring were produced. The F2 phenotypes and numbers were:
AEr
aER
aer
aEr
AeR
AER
Aer
aeR
197
201
45
51
49
55
199
203
Which genes are linked and what are the recombination frequencies between each pair of genes?