SAMPLE EXAM QUESTIONS - PART 1

Some multiple choice questions are included here, although they are unlikely to appear on exams). The rationale is that they are good ways to drill specific pieces of information quickly and directly.

1. Compare and contrast (define or describe each element, and show how they are similar and how they differ from each other; be sure to focus on the important points; an illustrative example often helps):

anaphase of mitosis - anaphase of meiosis I

anaphase of mitosis - anaphase of meiosis II

anaphase I - anaphase II

mitosis - meiosis II

meiosis I - meiosis II

anaphase I - anaphase II - mitotic anaphase

Note: why do you think anaphase figures so heavily in these questions? Also - any phase of mitosis & meiosis might be compared!

gene - allele

phenotype - genotype

random segregation - independent assortment

chromosome - DNA

replication - transcription - translation

2. Explain why we can use statistical methods to predict the genotypes of eggs (or other macrogametes) when each meiotic event results in only one of the four products surviving to maturity and potential contribution to a zygote. [It may help your explanation to include "why is this even a question -- what does it mean?]

3. Define or describe a testcross:

(a) distinguish it from other types of cross, and

(b) demonstrate the utility of a testcross.

(hint: a series of crosses might help here - as long as you explain what they illustrate!)

4. Demonstrate the utility of a testcross. Why are sex-linked genes easier to study than autosomal genes? (hint: a series of illustrative crosses might help here - as long as you explain what they illustrate!)

5. In an organism with a diploid number of 20 chromosomes, how many chromosomes and chromatids would be found in each cell at these stages?

1. A female fruit fly with abnormal (abe) brown (bis = bistre) eyes is crossed with a wild type male. All daughters are wild type; all sons have abnormal brown eyes. When the F₁ are crossed among themselves, the following are obtained:

2. Fill in the following chart. (HINT: do the Punnett squares)

 What is the linkage arrangement of these genes? Include whether they are on an autosome or X-linked (and why). What are the genotypes and phenotypes of the grandparental and parental generations? [suggestion: diagram the crosses]

a. What genotypes and phenotypes are present in the F₁, and in what proportions?

b. What offspring phenotypes would result, and in what proportions, if the F₁ were testcrossed?

c. Which are the "parental" types?

---- Non-parental?

d. If genes a and b were 10 map units apart, would your answer change? If so, what would the new answer be?

e. If genes a and b were not linked, would your answer change? If so, what would the new answer be?

5. Draw a brief pedigree which unambiguously demonstrates:

a. a recessive autosomal allele

b. a dominant autosomal allele

c. a recessive lethal allele

c. a dominant lethal allele

d. an X-linked dominant allele

e. an X-linked recessive allele

If it is not possible to demonstrate a particular situation unambiguously, explain (and/or demonstrate) why not, and demonstrate a plausible pedigree, even if it is not unambiguous

6. Be able to interpret pedigrees - the nomenclature, and the logic of transmission. See the textbook for examples, both within the chapter, and at the end in the problem portion.

7. You want to do a series of experiments using medflies because they reproduce fairly rapidly, among other things. Your field-collected flies are almost all wild type, but a few are mutant phenotype at a known recessive locus. How would you go about isolating homozygous dominant and homozygous recessive flies to begin a colony? Why is important to isolate these particular genotypes? Would you need to isolate heterozygotes before beginning your mating experiments? Explain.

III.   X ², probability

2. How would you rule out or test the proffered choices - explain your logic - and what is the genotype and linkage arrangement best supported by the data given?

3. The offspring of GgHh x gghh are: 82 GH, 96 Gh, 123 gH, 130 gh. The MOST LIKELY explanation is:

4. The offspring of GgHh x gghh are: 543 GH, 607 Gh, 523 gH, 487 gh. The MOST LIKELY explanation is:

5. It is now possible to test people for heterozygosity of the cystic fibrosis (cf) gene. Two known heterozygotes are married, and plan to have six children. What is the probability that they will have

a. four girls?
b. exactly one child with cf?
c. that the third and fifth children have cf, but the others are normal?
d. three with cf?
e. five with cf?
f. only one boy?
g. only one boy, and three children with cf?
h. only one boy, and three children with cf?
i. only one boy, and he is the only child with cf?

6. Two people of normal phenotype have had a child with Niemann-Pick disease, a lethal recessive trait.

a) What is the probability that their next child will be afflicted?
b) If they have three more children, what is the probability that they will have one more child with Niemann-Pick disease?
c) Two more?
d) All three?
e) That the first two will be normal but the third will be afflicted?

7. Using the equation ⁿp_x = [  n! (p^x)(q^n-x) ] / [ x!(n-x)! ] , calculate the probability of a monohybrid cross resulting in

IV. Three point crosses

Solve the following mapping problems. Your final answers should include the genotypes and phenotypes of both parents, with the genes arranged in the correct order and in the correct allelic configuration (i.e. dominant and recessive alleles arranged properly on each chromosome). Map distances and interference must also be calculated.

1. The offspring of a testcross had the following phenotypes. Describe as fully as possible the genetic map, including the most likely parents' genotypes and phenotypes, autosomal or sex-linked, map distances, interference, etc.

males females

+ + + 30 1010

+ + lz 32

+ ct + 441

+ ct lz 1

v + + 0

v ct lz 39

v ct + 27

v + lz 430

3. Analyze the following three-point cross: GgHhRr X gghhrr:

offspring phenotypes

GHR 112

GHr 66

GhR 811

Ghr 4

gHR 7

gHr 820

ghR 63

ghr 117

Are the number of double crossovers more, less, or the same as expected?

4. The offspring of a testcross had the following phenotypes. Describe as fully as possible the genetic map, including the most likely parents' genotypes and phenotypes, autosomal or sex-linked, map distances, interference, etc.

5. Goop syndrome results from the simultaneous expression of several linked genes for bad manners and poor grooming. Among these genes are those for chewing noisily, speaking loudly, and for failing to return borrowed items (see attached). Happily, the predominant phenotype does not express any of these traits. From a large number of testcrosses of polite individuals known to be heterozygous at all three of these loci (and sharing the same linkage arrangement) the following data were gathered:

6. The rate of recombination between genes which are far apart on a chromosome should be fairly high, but observed recombination frequencies are often lower than expected because
a. an even number of crossovers results in a recombinant phenotype
b. an odd number of crossovers results in a recombinant phenotype
c. an odd number of crossovers results in a nonrecombinant phenotype
d. an even number of crossovers results in a nonrecombinant phenotype
e. none of the above affect observed recombinant frequencies
f. interference

Explain:

V. Other exceptions to Mendelian "laws"

1. Give an example of epistasis (it may be imaginary). Indicate the phenomenon of epistasis. Show how such a phenotypic relationship might be explained by the underlying biochemistry. [obviously, this question could be asked about any number of phenomena]

2. In chickens, two different genes govern comb shape. The genotype R-P- produces walnut comb, R-pp rose comb, rrP- pea comb, and rrpp single comb.

a. How many genotypes will produce walnut comb? which ones?

b. A cross between walnut and rose parents produces 31 walnut, 28 rose, 10 pea, and 9 single comb offspring. What genotypes are the parents? explain (show work)

c. If chickens with walnut, rose, and pea combs are readily available in all genotypic conditions (and these conditions are known), which would you choose to mate to produce the highest proportion of single comb offspring? Why?

VI. Mapping using haploid organisms; somatic cells

1. Two strains of baker's yeast (Saccharomyces cerevisiae), differing at two linked loci, were crossed. The following unordered tetrads were counted:

a)

Multiple choice: Choose the single BEST answer.

1. Homologous chromosomes have the same _____ in the same _____
a. genes .... loci
b. alleles .... loci
c. alleles .... genes
d. loci .... genes
e. DNA .... genes

2. To determine the distance between three genes, a,b, and c,
a. only one dihybrid cross is necessary
b. two different dihybrid crosses are necessary: a - b and b - c
c. three dihybrid crosses are necessary: a-b, b-c, and a-c
d. each of these genes must be mapped with respect to a fourth gene, d
e. one cannot map three genes using dihybrid crosses

3. DNA synthesis occurs
a. during interphase before meiosis
b. during interphase before mitosis
c. during prophase of mitosis
d. a and b
e. all of the above

4. Pink four o'clocks are heterozygous for red/white flower color. This illustrates the phenomenon of
a. co-dominance
b. multiple alleles
c. multiple genes
d. Mendelian dominance and recessiveness
e. incomplete (partial) dominance

5. Differential penetrance or expressivity may be explained by different alleles with different
a. gene products
b. levels of expression
c. times of expression
d. responses to negative feedback
e. any of the above might be at work

6. Two genes do not exhibit linkage in dihybrid crosses if:
a. they are very far apart on the same chromosome
b. they are on different chromosomes
c. the recombinant frequency (RF) between them is > 0.5
d. a and b
e. all of the above

7. Two genes can exhibit linkage in dihybrid crosses only if
a. they are far from each other on the same chromosome
b. they are on different chromosomes
c. the recombinant frequency (RF) between them is > 0.5
d. they are close to each other on the same chromosome
e. the recombinant frequency between them = 1.0

8. Which of the following characterizes mitotic metaphase?
a. DNA synthesis
b. centriole migration to opposite poles
c. chromosome attachment to spindle apparatus at the equatorial plate
d. homologous chromosomes pairing
e. all of the above

9. Crossing over and recombination is most likely to occur between genes
a. located close to one another on a chromosome
b. on two different (non-homologous) chromosomes
c. that are functionally related to each other
d. located far from one another on a chromosome
e. recombination only occurs within genes

10.A man with a rare recessive disease marries a woman who is phenotypically normal. If the woman is homozygous at that locus, what is the probability that their offspring will have the disease?
a. 0% because the disease is rare
b. 0% because the child will receive a dominant allele from the mother
c. 100% because the child would receive the trait from the father
d. 50%
e. 25%

11. A child of the parents described in #7 marries a heterozygote at this locus. The probability that they will have a child with the disease is:
a. 0% because the disease is rare
b. 0% because the child will receive a dominant allele from the mother
c. 100% because the child would receive the trait from the father
d. 50%
e. 25%

12. In venutians, curly toes (S) are dominant over straight (s), red noses (P) are dominant over purple (p), and blue lips (M) are dominant over magenta (m). Assuming that these genes assort independently and follow Mendelian rules, what proportion of the progeny from a cross of a triply homozygous dominant individual and a triply homozygous recessive individual would be heterozygous for all three traits?
a. 0.25
b. 0.50
c. 0.67
d. 0.75
e. 1.00

13. Homologous chromosomes are found next to each other during
a. prophase I of meiosis
b. metaphase of mitosis
c. metaphase II of meiosis
d. interphase
e. homologous chromosomes are always next to each other

14. Which of the following cell types are capable of mitosis?
a. haploid
b. diploid
c. prokaryotic
d. a and b
e. all of the above

15. The standard or "normal" genotype and/or phenotype for an organism is
a. heterozygous
b. homozygous dominant
c. homozygous recessive
d. wild type
e. mutant

16. If two SsPpMm venutians mated, what proportion of their offspring would be expected to be SSppMm?
a. 1/2
b. 1/8
c. 1/16
d. 1/32
e. none of the above

17. A qR/Qr female that underwent one crossover event (between these two genes) during meiosis could produce which of the following gametes?
a. qr and QR only
b. qR and Qr only
c. Qq and Rr only
d. QR, Qr, qR, and qr
e. Q, q, R, and r

18. In a dihybrid testcross in which the progeny were observed for the presence of two linked genes, 200 recombinant phenotypes were observed out of 2401 progeny. How far apart are the two genes?
a. 2 m.u.
b. 2.4 m.u.
c. 8.5 m.u.
d. 12 m.u.
e. 20 m.u.

19. Two genes are known to be 10 map units apart. The expected percentage of nonparental (recombinant) offspring from a testcross is
a. 1%
b. 5%
c. 10%
d. 20%
e. not enough information given

20. Two genes are known to be 53.8 map units apart. The expected percentage of nonparental (recombinant) offspring from a dihybrid testcross is:
a. 25%
b. 26.9%
c. 50%
d. 53.8%
e. not enough information given

21. When red kernel corn and white kernel corn are crossed, the F₁ is pink, and the F₂ has red, light red, pink, light pink, and white kerneled corn. This is an example of
a. epistasis
b. codominance: two alleles of one gene
c. partial dominance: two alleles of one gene
d. multiple gene activity without epistasis
e. Mendelian dominance and recessiveness

22. Which of the following cell types are capable of meiosis?
a. haploid
b. diploid
c. prokaryotic
d. a and b
e. all of the above

23. Two genes control hair color in mice: if neither gene is homozygous recessive, the hair is agouti; if one gene is homozygous recessive hair is cinnamon; if the other gene is homozygous recessive hair is black; and if both genes are homozygous recessive, brown hair is grown. This is an example of
a. epistasis
b. codominance
c. partial dominance
d. multiple gene activity without epistasis
e. Mendelian dominance and recessiveness

24. A gene determines an individual's potential to develop a particular phenotype. This potential may be affected by
a. other genes
b. environment
c. evolution
d. a and b
e. all of the above

25. Given a cross between MmPPrrTtDdGg x MmPpRRTTDdgg, what is the chance of an offspring heterozygous at all of these loci?
a. 0
b. 1/6
c. 1/16
d. 1/32
e. 1/64

26. Given a cross between MmPPrrTtDdGg x MmPpRRTTDdgg, what is the chance of an offspring homozygous at all of these loci?
a. 0
b. 1/6
c. 1/16
d. 1/32
e. 1/64

27. Given a cross between MmPPrrTtDdGg x MmPpRRTTDdgg, what is the chance of an offspring expressing the dominant phenotype for all six traits?
a. 0
b. 1
c. 9/32
d. (1/2)⁶
e. (3/4)⁶

28. a and b are linked autosomal genes whose recombinant frequency is 5%. c and d are X-linked genes, 10 map units apart. A homozygous dominant female is crossed with a recessive male; the F₁ females are backcrossed. Which of the following would be expected for the testcross progeny?
a. nearly equal frequency of a⁺bc⁺d⁺, a⁺bcd, ab⁺c⁺d⁺, ab⁺cd classes
b. independent segregation of some genes with respect to some others
c. different ratios in males and females
d. a and b
e. all of the above

29. In the system described above, what proportion of testcross offspring would be expected to be phenotypically a⁺bcd⁺?
a. 0.25%
b. 0.5%
c. 5%
d. 10%
e. 45%

30. A triply wild-type female mated with a triply recessive mutant male gives rise to a large number of offspring. All of the offspring are wildtype. Among the F-1, the males represent many different phenotypes, but the females are all wildtype. This indicates
a. the genes are sex-linked; the mother was heterozygous at all 3 loci
b. the genes are sex-linked; the mother homozygous dominant
c. the genes are sex-linked but this is a ZZ/ZW organism: the female is hemizygous
d. the genes are autosomal
e. not enough information given

31. If the genes above are linked, which mating would allow the best mapping?
a. the F-1
b. the female P-1 with the F-1 male
c. the female F-1 with the P-1 male
d. one would have to find another strain altogether - none of these are helpful
e. the genes are not linked

32. The centromere can be mapped by analysis of
a. ordered tetrads
b. unordered tetrads
c. trihybrid crosses
d. all of the above
e. none of the above - only by microscopy

33. When analyzing non-ordered tetrads
a. tetratypes represent single crossover events only
b. parental ditypes result only from mitosis with no cross over
c. non-parental ditypes result only from double cross-over events
d. double cross-over events result only in non-parental ditypes
e. single cross over events can result in tetratypes or parental ditypes

34. Male pattern baldness demonstrates the phenomenon of
a. sex linked gene activity
b. sex influenced gene activity
c. sex limited gene activity
d. autosomal gene activity
e. epigenetic gene activity

35. Estrogen secretion demonstrates the phenomenon of
a. sex linked gene activity
b. sex influenced gene activity
c. sex limited gene activity
d. autosomal gene activity
e. epigenetic gene activity

36. Food preference demonstrates the phenomenon of
a. sex linked gene activity
b. sex influenced gene activity
c. sex limited gene activity
d. autosomal gene activity
e. epigenetic gene activity

37.  Karyotype analysis can determine all of the following EXCEPT
a. gender
b. trisomy
c. monosomy
d. presence of a recessive allele
e. loss of a piece of a chromosome

38. Which of the following cells or tissues is typically used for karyotypes?
a. amniotic cells (in amniotic fluid -- amniocentesis)
b. chorionic villus cells (chorionic villus sampling)
c. white blood cells
d. a and b
e. all of the above

39. An abnormal condition in which one extra or one too few chromosomes is present is called
a. euploidy
b. aneuploidy
c. monosomy
d. trisomy
e. haploidy

40. Which of the following is NOT a good example of a selectable marker?
a. an antibiotic resistance allele
b. an allele which noticeably alters the phenotype of the cell
c. an allele for making an amino acid
d. an allele for catabolizing a nutrient
e. all of the above would be good