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Genetics 2011, Midterm Exam
1. Assuming independent assortment, which of the crosses below will give a 3:3:1:1 ratio?
A) AABB x aabb
B) AaBb x Aabb
C) AaBb x aabb
D) AaBB x aaBb
E) Aabb x aaBb
2. Suppose that a husband and wife are both heterozygous for a recessive allele that defines albinism. If they have dizygotic (twoegg) twins, what is the probability that both of the twins will have different phenotypes for pigmentation ?
A) 3/4
B) 9/16
C) 3/8
D) 5/8
E) 1/4
3. How many phenotypic classes of progeny will be produced in the cross below?
A/a; B/b; C/C; D/d x A/a; b/b; c/c; d/d
A) 8
B) 4
C) 16
D) 32
E) 128
4. An organism has a diploid chromosome number 2n = 8. How many centromeres are present in a cell during (note: not before, not
after, but during) Anaphase II of meiosis ?
A) 32
B) 8
C) 4
D) 64
E) 16
5. Some alleles that determine the ABO blood group types in humans demonstrate
A) complete dominance
B) recessiveness
C) co-dominance
D) a modified monohybrid-cross phenotypic ratio
E) all of the above
6. Incomplete dominance in a heterozygote:
A) phenotype is determined by both dominant alleles
B) phenotype is fully determined just by one dominant allele
C) phenotype is to some extent determined by a dominant allele
D) phenotype is determined by recessive allele
E) phenotype is determined by both recessive alleles
7. Mendel’s first and second laws state that:
A) during gamete formation pairs of alleles segregate equally and alleles assort independently
B) during gamete formation alleles segregate equally and pairs of alleles assort independently
C) in diploid organisms all pairs of alleles segregate equally and assort independently
D) in diploid organisms there is a haploid stage
E) in haploid organisms there is a diploid stage when meiosis occurs
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Your Name:
Genetics 2011, Midterm Exam
8. Which of the following is a true statement about meiosis or mitosis?
A) in prophase of meiosis homologous chromosomes pair up (synapse)
B) in anaphase I of meiosis alleles segregate
C) in metaphase I of meiosis paired homologs occupy the equatorial plane
D) in anaphase II of meiosis sister chromatids separate from each other
E) all of the above
9. In mice, dwarfism is caused by an X-linked recessive allele, and yellow coat is caused by an autosomal dominant allele (the normal
color is grey). Remember that the “yellow” allele is lethal when homozygous. A dwarf yellow female is crossed to a yellow normalsize male. What are the phenotypic ratios in the F1 in each sex?
A) 1/3 yellow normal ♀ : 1/3 yellow dwarf ♂ : 1/6 grey normal ♀ : 1/6 grey dwarf ♂
B) 9/16 yellow normal : 3/16 yellow dwarf : 3/16 grey normal : 1/6 grey dwarf
C) 3/8 yellow normal ♀ : 3/8 yellow normal ♂ : 1/8 grey dwarf ♀ : 1/8 grey dwarf ♂
D) 1/4 yellow normal ♀ : 1/4 yellow normal ♂ : 1/4 grey dwarf ♀ : 1/4 grey dwarf ♂
E) 1/4 yellow normal : 1/4 yellow dwarf : 1/4 grey normal : 1/4 grey dwarf, the same for each sex
10. Distance between locus A and locus B is 20 map units. How many recombinant progeny would be obtained in a test-cross of a
heterozygote AB/ab:
A) unpredictable
B) 25%
C) 3/4
D) 20%
E) 100%
11. What is the most likely mode of inheritance of the genetic trait in the pedigree below?
A) X-linked
B) autosomal recessive
C) X-linked dominant
D) autosomal dominant
E) Y-linked
recessive
12. Suppose that in a cross AB/ab x AB/ab (the loci are linked) the frequency of the progeny with a fully recessive phenotype is 16%.
What is map distance between the loci?
A) 16 mu
B) 20 mu
C) 32 mu
D) 40 mu
E) 8 mu
13. Self fertilization of several phenotypically tall F1 pea plants results in the production of 100 progeny: 79 tall and 21 short plants.
The hypothesis is that this represents a 3 : 1 ratio. Given this hypothesis, what is the probability that the deviation from expectations
is due to chance?
A) 10% < P < 50%
B) 0% < P < 1%
C) 1% < P < 5%
D) 5% < P < 10%
E) 50% < P < 90%
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Your Name:
Genetics 2011, Midterm Exam
14. Complementation in a dihybrid cross can be thought to occur when
A) a 9:7 ratio was seen in F2
B) a cross of two mutants produced a wild type F1 phenotype
C) a 12:3:1 ratio was seen in F2
D) only two answers above are correct
E) none of above
15. Flowers in a certain plant are normally red. Several plants with white petals have been isolated as spontaneous mutants and the
white phenotype has been shown to be inherited as a Mendelian autosomal recessive in each case. Two white-petal pure-breeding
plants were crossed, the F1 progeny was all red. Then, the F2 is expected to be
A) all red as well
B) all white
C) 3/4 red, 1/4 white
D) 1/2 red, 1/2 white
E) 9/16 red, 7/16 white
16. Let’s assume that two parental organisms of the genotypes AA BB and aa bb were crossed. The obtained F1 progeny was
testcrossed. About 25% of the testcross progeny showed the same phenotype as one of the original parents. This indicates that the
gene locus A and the gene locus B are:
A) localized on different chromosomes
B) linked at a distance exceeding 50 m.u.
C) linked at about 50 m.u. distance
D) assort independently
E) any of the above statements can be correct
17. A trait is defined by a dominant allele D. Out of ten individuals who inherited this allele, only eight show the trait phenotypically.
Moreover, in two of them the D phenotype is barely noticeable, in three of them it is mildly pronounced and in the remaining three,
the trait is fully developed. The correct term to describe this situation is:
A) incomplete dominance and recessive epistasis
B) dominant epistasis
C) incomplete penetrance and variable expressivity
D) multiple alleles
E) experimental error
18. Suppose that loci R and S are linked, and are 6 mu apart on the linkage map of a mouse chromosome. You cross two parental
strains: RS/RS and rs/rs. The F1 mice are testcrossed and a total of 300 F2 progeny are produced. What is the number of mice in the
F2 that you expect to be of a recombinant type?
A) 6
B) 12
C) 3
D) 18
E) 9
19. Jack and Jill went up the hill, got married and had a baby. Jack’s parents’ genotypes were AB/AB (the baby’s grandma) and ab/ab
(grandpa). Jill’s genotype is ab/ab. Loci A and B are linked at 10 mu. What is the probability that Jack and Jill have a boy that looks
like the grandma with respect to the A and B phenotype?
A) 10%
B) 5%
C) 25%
D) 45%
E) 22.5%
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Your Name:
Genetics 2011, Midterm Exam
20. A cross of two wild type flies results in a ratio 2 females : 1 male among the progeny. What is the most likely explanation of this
result?
A) lethal Y-linked allele in the parental male
B) lethal X-linked allele in the parental female
C) this is not unusual: 50% of males often die off due to hemizygosity for X chromosome
D) lethal X-linked allele in the parental female
E) lethal autosomal allele in both parents
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