BIOL 2300 EXAM 2: QUIZ QUESTIONS
How do we know that specific genes are linked on a single chromosome, in contrast to
being located on separate chromosomes? - *the genes segregate together during
gamete formation*
Imagine that you have joined a genetics lab on campus and want to gain experience
mapping genes in Drosophila.
You conduct a series of two-point mapping crosses involving five genes located on
chromosome III and obtain the following percentage of recombinant offspring:
h-cu: 23.5%
eyg-h: 9.0%
eyg-cu: 14.5%
rai-eyg: 18.5%
rai-h: 9.5%
rai-cu: 33.0%
th-cu: 6.8%
th-h: 16.7%
th-eyg: 7.7%
th-rai: 26.2%
In a three‑point mapping experiment for the genes y‑w‑ec, the following percentages of
events are observed: NCO events: 65%; SCO events between y and w: 15%; SCO
events between y and ec: 17%; DCO events: 3% What is the map distance between y
and w? - *18 mu*
Assume that a cross is made between AaBb and aabb plants and that the offspring fall
into approximately equal numbers of the following groups: AaBb, Aabb, aaBb, aabb.
These results are consistent with ________. - *independent assortment*
Why are double-crossover events expected less frequently than single-crossover
events? - *the probability of two crossover events occurring at the same time is much
lower than the probability of one*
What is the difference between a genetic map and a physical map? - *A genetic map
gives the relative distance between genes based on recombination, and a physical map
gives actual locations of genes on chromosomes or a DNA sequence.*
The phenomenon in which one crossover decreases the likelihood of crossovers in
nearby regions is called - *positive interference*
Lod scores are used to predict which of the following? - *gene linkage*
, The genes dumpy (dp), clot (cl), and apterous (ap) are linked on chromosome II of
Drosophila. In a series of two-point mapping crosses, the following genetic distances
were determined.
dp-ap: 39
dp-cl: 3
ap-cl: 42
What is the sequence of the three genes? Enter your answer using the gene names dp,
ap, or cl and seperate each with a hyphen with no spaces. For example, if the question
used a, b, and c for gene names and you thought the oder was cab, you would enter
your answer as c-a-b.
Considering that rai is near the end of chromosome III, construct a map of these genes.
For (a), (b), (c), and (d), enter the correctly named gene, for example, if you think, eyg
goes in blank "d", then enter eyg. Order your genes by their distance to rai, with the
gene closest to rai going in blank a and the gene most distant going in blank d. For
blanks 1, 2, 3, and 4, enter the map distances for the respective genes. For example,
the distance in blank 1 would be the distance between rai and the gene you entered in
bla - a) *h*
b) *eyg*
c) *th*
d) *cu*
1) *9.5*
2) *9.0*
3) *7.7*
4) *6.8*
The genes for mahogany eyes and ebony body are approximately 25 map units apart
on chromosome 3 in Drosophila. Assume that a mahogany-eyed gray bodied female
was mated to an red eyed ebony-bodied male and that the resulting F 1 phenotypically
wild-type (red eyed, gray bodied) females were mated to mahogany, ebony males to
obtain an F 2 generation. Which of the following phenotypes would be expected in the F
2 offspring? Hint: Really pay attention to what the question is asking you to cross -
approach this in a step-wise fashion and you should be fine......... - *red eyed, gray
bodied*
*mahogeny eyed, gray bodied*
*red eyed, ebony bodied*
*mahogeny eyed, ebony bodied*
When Morgan carried out crosses involving two X-linked genes in Drosophila, he
sometimes observed new phenotypes that were not present in the parents. What did
Morgan propose from these observations? - *The points of overlap between synapsed
homologous chromosomes, called chiasmata, were points of genetic exchange.*
Genetic distances within a given linkage group: - *cannot exceed 50 cm*
How do we know that specific genes are linked on a single chromosome, in contrast to
being located on separate chromosomes? - *the genes segregate together during
gamete formation*
Imagine that you have joined a genetics lab on campus and want to gain experience
mapping genes in Drosophila.
You conduct a series of two-point mapping crosses involving five genes located on
chromosome III and obtain the following percentage of recombinant offspring:
h-cu: 23.5%
eyg-h: 9.0%
eyg-cu: 14.5%
rai-eyg: 18.5%
rai-h: 9.5%
rai-cu: 33.0%
th-cu: 6.8%
th-h: 16.7%
th-eyg: 7.7%
th-rai: 26.2%
In a three‑point mapping experiment for the genes y‑w‑ec, the following percentages of
events are observed: NCO events: 65%; SCO events between y and w: 15%; SCO
events between y and ec: 17%; DCO events: 3% What is the map distance between y
and w? - *18 mu*
Assume that a cross is made between AaBb and aabb plants and that the offspring fall
into approximately equal numbers of the following groups: AaBb, Aabb, aaBb, aabb.
These results are consistent with ________. - *independent assortment*
Why are double-crossover events expected less frequently than single-crossover
events? - *the probability of two crossover events occurring at the same time is much
lower than the probability of one*
What is the difference between a genetic map and a physical map? - *A genetic map
gives the relative distance between genes based on recombination, and a physical map
gives actual locations of genes on chromosomes or a DNA sequence.*
The phenomenon in which one crossover decreases the likelihood of crossovers in
nearby regions is called - *positive interference*
Lod scores are used to predict which of the following? - *gene linkage*
, The genes dumpy (dp), clot (cl), and apterous (ap) are linked on chromosome II of
Drosophila. In a series of two-point mapping crosses, the following genetic distances
were determined.
dp-ap: 39
dp-cl: 3
ap-cl: 42
What is the sequence of the three genes? Enter your answer using the gene names dp,
ap, or cl and seperate each with a hyphen with no spaces. For example, if the question
used a, b, and c for gene names and you thought the oder was cab, you would enter
your answer as c-a-b.
Considering that rai is near the end of chromosome III, construct a map of these genes.
For (a), (b), (c), and (d), enter the correctly named gene, for example, if you think, eyg
goes in blank "d", then enter eyg. Order your genes by their distance to rai, with the
gene closest to rai going in blank a and the gene most distant going in blank d. For
blanks 1, 2, 3, and 4, enter the map distances for the respective genes. For example,
the distance in blank 1 would be the distance between rai and the gene you entered in
bla - a) *h*
b) *eyg*
c) *th*
d) *cu*
1) *9.5*
2) *9.0*
3) *7.7*
4) *6.8*
The genes for mahogany eyes and ebony body are approximately 25 map units apart
on chromosome 3 in Drosophila. Assume that a mahogany-eyed gray bodied female
was mated to an red eyed ebony-bodied male and that the resulting F 1 phenotypically
wild-type (red eyed, gray bodied) females were mated to mahogany, ebony males to
obtain an F 2 generation. Which of the following phenotypes would be expected in the F
2 offspring? Hint: Really pay attention to what the question is asking you to cross -
approach this in a step-wise fashion and you should be fine......... - *red eyed, gray
bodied*
*mahogeny eyed, gray bodied*
*red eyed, ebony bodied*
*mahogeny eyed, ebony bodied*
When Morgan carried out crosses involving two X-linked genes in Drosophila, he
sometimes observed new phenotypes that were not present in the parents. What did
Morgan propose from these observations? - *The points of overlap between synapsed
homologous chromosomes, called chiasmata, were points of genetic exchange.*
Genetic distances within a given linkage group: - *cannot exceed 50 cm*
