Assigned Study Questions Due on Monday, April 9, 2007
Correct Answers are provided – you’ll be evaluated for your ability to discuss the reasons that
this answer is correct and the reasons that each of the other answers is incorrect.
The following questions refer to the data below for Crosses I and II:
CROSS I. Purebred lines of wild-type fruit flies (gray body and normal wings) are mated to flies
with black bodies and vestigial wings. F1 offspring all have a wild-type phenotype.
CROSS II. F1 flies are crossed with flies recessive for both traits (a testcross).
Resulting Offspring
Gray body; normal wings
Black body; vestigial wings
Black body; normal wings
Gray body; vestigial wings
Normal
575
571
577
568
Percentage
25.1
24.9
25.2
24.8
KEY:
A. CROSS I results give evidence supporting the statement.
B. CROSS I results give evidence against the statement.
C. CROSS II results give evidence supporting the statement.
D. CROSS II results give evidence against the statement.
E. Neither CROSS I nor CROSS II results support the statement.
8) Vestigial wings are a recessive trait.
Answer: A
9) The genes for body color and wing shape are linked.
Answer: D
10) An F1 cross should produce flies that will fall into a Mendelian 9:3:3:1 ratio .
Answer: C
11) There are 25 centimorgans (map units) between the genes for body color and wing shape.
Answer: D
12) A 0.1% frequency of recombination is observed
A) only in sex chromosomes.
B) only on genetic maps of viral chromosomes.
C) on unlinked chromosomes.
D) in any two genes on different chromosomes.
E) in genes located very close to one another on the same chromosome.
Answer: E
13) The following is a map of four genes on a chromosome:
A
5
W
3
E
G
12
Between which two genes would you expect the highest frequency of recombination?
A) A and W
B) W and E
C) E and G
D) A and E
E) A and G
Answer: E
14) The reason that linked genes are inherited together is that
A) they are located on the same chromosome.
B) the number of genes in a cell is greater than the number of chromosomes.
C) chromosomes are unbreakable.
D) alleles are paired.
E) genes align that way during metaphase I.
Answer:
15) What is the mechanism for the production of genetic recombinants?
A) X inactivation
B) methylation of cytosine
C) crossing over and independent assortment
D) nondisjunction
E) deletions and duplications during meiosis
Answer: C
16) There is good evidence for linkage when
A) two genes occur together in the same gamete.
B) a gene is associated with a specific phenotype.
C) two genes work together to control a specific characteristic.
D) genes do not segregate independently during meiosis.
E) two characteristics are caused by a single gene.
Refer to the following table to answer the following questions.
Gene
b
cn
rb
vg
0
5
3.5
19
b
0
6.5
9
cn
0
16
rb
0
vg
Answer: D
b = black body
cn = cinnabar eye
rb = reduced bristles
Vg = vestigal wings
The numbers in the boxes are the recombination frequencies in between the genes (in %)
17) In a series of mapping experiments, the recombination frequencies for four different
linked genes of Drosophila were determined as shown in the table. What is the order of these
genes on a chromosome map?
A) rb-cn-vg-b
B) vg-b-rb-cn
C) cn-rb-b-vg
D) b-rb-cn-vg
E) vg-cn-b-rb
Answer: D
18) Which of the following two genes are closest on a genetic map of Drosophila?
A) b and vg
B) vg and cn
C) rb and cn
D) cn and b
E) b and rb
Answer: E
X, Y, and Z are three genes in Drosophila. The recombination frequencies for
two of the three genes are shown below.
Gene Pair
X-Y
X-Z
Y-Z
Recombination Frequency
50%
25%
?
19) Genes X and Y could be
A) located on different chromosomes.
B) located very near to each other on the same chromosome.
C) located far from each other on the same chromosome.
D) both A and B
E) both A and C
Answer: E
20) If the recombination frequency for Y and Z was found to be 50%, this would mean that
A) genes X and Y are on the same chromosome.
B) genes X and Y are on different chromosomes.
C) genes Y and Z are on different chromosomes.
D) both A and C.
E) both B and C
Answer: E
21) Which of the following is true regarding linkage maps? They
A) always have a total of 100 map units.
B) can be used to pinpoint the precise physical position of a gene on a chromosome.
C) are a genetic map based on recombination frequencies.
D) require preparation of karyotypes.
E) reflect the frequency of crossing over between X and Y chromosomes.
Answer: C
22) The frequency of crossing over between any two linked genes is
A) higher if they are recessive.
B) different between males and females.
C) determined by their relative dominance.
D) the same as if they were not linked.
E) proportional to the distance between them.
Answer: E
23) Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in
Drosophila by showing that
A) there are four major functional classes of genes in Drosophila.
B) Drosophila genes cluster into four distinct groups of linked genes.
C) the overall number of genes in Drosophila is a multiple of four.
D) the entire Drosophila genome has approximately 400 map units.
E) Drosophila genes have, on average, four different alleles.
Answer: B
24) Map units on a linkage map cannot be relied upon to calculate physical distances on a
chromosome because
A) the frequency of crossing over varies along the length of the chromosome.
B) the relationship between recombination frequency and map units is different in every
individual.
C) physical distances between genes change during the course of the cell cycle.
D) the gene order on the chromosomes is slightly different in every individual.
E) all of the above
Answer: A