Download doc Conference #5 Problems

A) There is a specific protozoan than can only survive on pizza (Dinoflagella bigassium).
Here is the chromosomal arrangement of the Roman variety:
1 2 3o4 5 6
o7 8 9
And of the Brooklyn kind:
1 2 3o4
5 9 5 9o7 8 6
Propose a mechanism explaining these changes in the fewest possible steps.
B) Two restaurants, one in Detroit, the other in Minneapolis are both renown for their
pizza. Each chef claims the “pizza making” tradition in their city inspired the other to
start making pizzas, implying that they deserve the whole credit. You decide to get to the
bottom of it
Here is the Detroit variety:
1 2 3o4
5 9 8 7o10 11 6
Here is the Minneapolis one:
1 2 3o4
8 7o9 5 6
If you knew that no more than 2 major rearrangements could separate the Brooklyn
variety from any other in North America, what could you conclude?
Answer
A) In 3 steps:
1 2 3o4 5 6
Translocation
1 2 3o4 5 9
Duplication
1 2 3o4 5 9 5 9
Translocation
1 2 3o4
o7 8 9
o7 8 6
o7 8 6
5 9 5 9o7 8 6
B) Both must have had a pericentric inversion leading to an intermediary hypothetical
common ancestral genome:
1 2 3o4
5 9 8 7o9 5 6
Genes 5 and 9, being duplicated could either evolve more specialized functions into
genes 10 and 11 (in Detroit) or be gradually lost as the genome streamlined (in
Minneapolis).
Conclusion: Neither influenced the other, the credit belongs to wherever the hypothetical
common ancestor will be found (most probably Chicago!).
Q. You are a mad British scientist and you have isolated a line of chimpanzees that are
highly prone to rage. During an incident where one of your technicians was fiercely
attacked and disembowelled by one of the rage affected chimps, you discovered that your
dart guns filled with poison sauce X™ (used to great success on rats around the lab) were
completely ineffective in bringing the wild-eyed beast down.
After hiring a new technician, you wish to identify which chromosome contains
the rage gene, so you can sequence it and sell it for evil to the highest bidder. You decide
to try using the somatic cell hybridization method you learned back at McGill. You
hybridize cells from your chimp with rodent cells and, obtain the following results:
Cell Line
ZOMB-11
Hitch-3d
FRI-13
28-Day-L
Romero-666
Slash-56
Evildead-2
Raimi-S34
Poe-26
Growth on Poison sauce X™
+
+
+
+
Chimp Chromosomes Present
1,2,5,6,7,8,9,15,16,19,23,X
3,4,6,7,9,13,16
4,5,7,9,12,13,14,16,19,21,X
1,2,5,9,t(10,6),12,16,19,20,22
1,6,8,23,16,20,X
1,2,3,4,8,9,10,14,16,18,20,21,22,X
5,9,16,17,20,X
2,3,4,5,10,16
5,6,7,9,10,11,12,16,X
1. On which chromosome is the rage gene located?
2. If you are bitten by a chimpanzee with the rage phenotype, should you be
concerned that you may be the epicentre of a devastating rage pandemic?
Answers:
1. Chimpanzee chromosome 6
2. No, rage is a genetic trait of the chimpanzee and is hence not transmittable to
humans by biting.
Chromosomes are always numbered in order of size (in humans 1 being largest, 22 being
smallest). Several lines of evidence show that humans shared a common ancestor with
chimpanzees between 5-6 million years ago, and that we shared a common ancestor with
gorillas between 7-8 million years ago.
1) Based solely on this image, what would you expect the diploid chromosome
number to be in gorillas and chimpanzees?
2) What is the most likely range of time in which this major change occurred?
3) What would we expect to find at position A in the human chromosome 2?
4) You discover that at position B, the segment in gorillas has been inverted and the
orientation flipped around…what is this called and what is the range of time in
which it most likely occurred?
5) Based on the dates mentioned above since a shared common ancestor, are
chimpanzees more closely related to humans or gorillas?
Answers:
1) Based on the banding patterns we can see that the human chromosome 2 is the
result of a fusion between two chromosomes. Therefore we can expect gorillas
2)
3)
4)
5)
and chimps to have an extra chromosome, in the diploid state then, they would
have 46 autosomes as well their sex chromosomes…48 (which is their actual
number)
Given that only humans seem to have this chromosome fusion, it is
overwhelmingly more likely that this occurred once in the human lineage
(orangutans also don’t have this fusion) rather than three chromosome breaks in
gorilla, chimp and orangutan lineages. Therefore it would have happened after the
split between humans and chimps.
If it was a fusion rather than two separate deletions, there would be a vestigial
centromere here in humans (which is actually found there in reality)
It is called an inversion, if it is only found in the gorilla, then it most likely
occurred once in the gorilla lineage after it split with the ancestor that it shared
with humans and chimps 7-8 million years ago
Humans and chimpanzees shared a common ancestor more recently than humans
and gorillas as well as chimps and gorillas which also would have shared a
common ancestor between 7-8 million years ago. Therefore, gorillas split from
the lineage that led to humans and chimpanzees first. Although chimps and
gorillas are more similar than chimps and humans in terms of this chromosome
fusion, chimps share more genomic characteristics with humans on the whole then
they do with gorillas.
You have been charged with determining the chromosomal location of the gene coding
for cyanide resistance in humans. The C.I.A is funding you and hoping you will then
develop a simple screening protocol that they can use on prospective spies before entry
into their training program. Because you have tons of money and want to learn new
techniques you take a shot in the dark and hybridize human cells that are resistant to
cyanide and can metabolize petroleum jelly with mouse cells that can metabolize
menthol. You grow the different hybrid cell lines in petroleum jelly and menthol and
assay cell extracts for cytochrome c oxidase activity (the enzyme affected by cyanide) in
the absence and presence of cyanide. On what chromosome is the cyanide resistance
gene located? How about the gene conferring the ability to metabolize petroleum jelly
(the selectable marker)? Why do you need to assay cyt c oxidase activity in the absence
of cyanide? Where is cyt c oxidase located?
Cell
Line
GM-22
THM-66
BM-02
JM-10
KM-44
RF-20
Cyt C Oxidase Activity
(Absence/Presence of
cyanide)
+/+/+
-/+/+/+
+/+
Chromosomes Present
2,14,6,18,20,21,X
1,6,8,9,12,15,18,21,22,X,Y
6,10,11,18
3,4,5,10,13,16,18,20,21,22,X
1,2,6,9,14,18,2,21,X
1,3,5,8,9,15,16,17,18,21
FC-16
JW-28
+/+/-
2,3,7,8,12,14,16,18,21,22,X,Y
1,3,7,12,17,18,20,21,22,X
ANSWER
Cyanide resistance must be conferred by a gene on chromosome 9. Petroleum jelly
metabolism must be conferred by a gene on chromosome 18 because it is the one
chromosome that all cells share. The cyt c oxidase assay in the absence of cyanide
allows you to confirm its presence in the cells. BM-02 allows you to say that cyt c
oxidase is on chromosome 21.
Part A
If meiotic non-disjunction in females occurs at first division, how many aneuploid
gametes present after the division? In addition, if normal meiotic division occurs
in the first division, but non-disjunction occurs during second division how many
aneuploid gametes are produced?
a. Two and Three
b. Two and One
c. Four and Two
d. One and Two
Part B
A fertile male individual (XYY), mates with a female (XX), what possible gametes
are produced?
a. 2 males (XY) and 2 females (XX)
b. 2 males (XYY) and 2 females (XX)
c. 3 males (XYY) and 1 female (XX)
d. 4 males (XXY)
Part C
A triplo-X triomics (XXX) females are phenotypically normal and fertile, if one
triplo-X femamle mates with a male (XY), list all possible genotypes for male and
female gametes.
Answers:
Part A – Non-disjunction at first division leads to two (n-1) and two (n+1)
chromosomes and at second division it leads to one (n-1) and one (n+1)
chromosome. The answer is C.
Part B – The second Y chromosome from the male does not pair and is not
transmitted to gametes. XYY is NOT Klinefelter's (XXY), Klinefelter males
are sterile. The answer is A. Refer to page 568 of text (9th edition).
Part C – The third X chromosome from the female also does not pair, so
possible gametes are females, XX and males, XY. Refer to page 568 of text
(9th edition),