Lesson #7 Chromosome Changes
AGRO 315 Genetics
Questions due Monday, February 27, 2012, 11:59pm
1.. Go to the on-line Karyotyping activity and then complete this question (find link on
Blackboard Lesson / Week #7 folder)
Match the patient with the chromosomal disorder.
Patient A_____
Patient B_____
Patient C ____
1. Klinefelters Syndrome
2. Turner’s Syndrome
3. Down’s Syndrome (non dysjunction type)
4. Down’s Syndrome (translocation type)
5. Trisomy 13 Syndrome
6. Normal karyotype (no obvious disorder)
2.. What are the three “morphological” features of a chromosome that a cytogeneticist
would use to perform the karyotype analysis you just completed?
___ length
___ presence of a specific gene on the chromosome
____ presence of a mutant allele on the chromosome ____centromere position
____ ability of the chromosome to cause a specific disorder ___ ‘banding’ pattern
3.
a. On the discussion board, describe how nondisjunction can result in each of the
syndromes above. Talk about the stage(s) of meiosis where non-disjunction could
occur and the end product of each scenario (what would the resultant gametes look
like).
b. If your sibling is shown to be a carrier of a 15/21 translocation that they inherited from
one of your parents, what is the chance that YOU are also a carrier of this same 15/21
translocation?
4. The diagram below shows some of the chromosomes in a Simmental bull who carries a
14/20 translocation. Assume chromosome 14 is not paired with any other chromosome in
this diagram.
a
a
A
A
b
b
B
Unpaired chromosome #14
B
Answer questions on the next page based on this diagram.
.a. What stage of cell division is depicted with the chromosomes above?
.b. In cattle 2N = 60. The number of chromosomes NOT depicted above is_______
c. Why does the bull have a normal phenotype (no syndrome)
d. What is the number of chromosomes this bull would have in its somatic cells.
e. Why does mitosis works fine but meiosis only “works” sometimes (semi sterile)
f. How could this bull could produce an offspring with a 2N=58 (hint if mated with…)
g. Why would cows or bulls with 2N=58 would be completely fertile?
5. View the cattle evolution presentation before answering this realistic but hypothetical
question.
.a. Assume that you are a USDA beef cattle geneticist and you are assigned to study
genetic resistance to a disease in cattle. No cattle breed or individual currently has
adequate genetic resistance to this disease. However, Asian animals that are “cattle-like”
have genetic resistance. You hypothesize that breeding to one of these may help produce
cattle that are genetically resistant.
a. Based on the karyotypes shown, which would make the best candidate to test this
hypothesis?
Circle one:
Banteng
Murrah Buffalo
b. Explain why you made the choice above.
Swamp Buffalo
6. Go to the cattle evolution presentation, then answer the question.
a. Assume you are an evolutionary biologist and very interested in understanding
the evolutionary history of Cattle, Banteng, Murrah Buffalo and Swamp Buffalo.
You propose the Evolutionary path of Bovid species below as your hypothesis.
Fill in the a, b and c with Banteng , Murrah Buffalo and Swamp Buffalo in the
appropriate space.
Bovid Evolutionary Genetics
a.________
and
Mutations and Selection
Ancestor
e ns
Fiv atio
c
s lo
n
Tra
2N = 60
Cattle
2N = 60
One
More
Translocation
b. ________
2N= ______
c. ________
2N= ______
7. a. A breeder/geneticists could test their hypothesis in question #6 in ______ years.
b. How would an evolutionary biologist ‘test’ the hypothesis above?
8. Draw a picture that would show how you could use FISH to compare cattle
chromosomes with the chromosomes of the other Bovid species and test your
evolutionary hypothesis of “translocation driven speciation.”
9. Mules are produced from crosses between female horses (Equus caballus, 2n= 64) and
male donkeys (Equus asinus, 2n= 62). A mule karyotype is shown below.
Metacentric / Submetacentric
Acrocentric
Telocentric
a. How many chromosomes should a mule have? _______
b. How many chromosomes would a trisomic donkey have?______
c. How many chromosomes would a monosomic horse have?________
d. How can you tell from the chromosome morphology that this karyotype is from a
mule and not a monosomic horse or trisomic donkey?
e. Would this be a female or male mule __________
f. Why are mules normally sterile?
f. Occasionally, fertile mules have been discovered. One possible explanation for their
fertility is that they are chimeric. They have the somatic cells of a mule but would have
the germline cells of a horse. Propose two experiments or procedures that could be
performed to test this hypothesis and the predicted results of each experiment.
10. Ringtail Possums have been captured from remote regions of Australia and brought
to zoos. Sometimes, males and females from different regions are mated and their
offspring are sterile. Use the karyotype below of two different Ringtail possums to
explain why. Describe how FISH could be used to test the hypothesis of two
translocations driving the evolution of a new Ringtail Possum species.
Polyploidy
11. Use the discussion board to order the karyotype diagrams (which will be
provided) and explain the evolution of bread wheat.
Cultivated Alfalfa
Diploid Alfalfa
The diagram below
shows the proposed cytogenetic history of bread wheat, which is an
2n = 16
______ diagrams to demonstrate
ploid
allohexaploid. Your TA will ask you to use a set 2n
of =karyotype
how cytogenetic evidence was used to assemble this evolutionary explanation.
Diploid T. monococcum
2n = 14
X
Diploid T. searsiii
2n = 14
Sterile hybrid
T. Turgidium
Diploid T. tauschii
2n = 14
X
2n =___
_________ploid Emmer Wheat
2n = ____
2n =___
Sterile hybrid
__________ploid T. aestivum
Bread Wheat
2n = ______
12. The cultivated watermelon Citrullus lanatusa is a diploid (2n = 22= somatic cell
number) but some people prefer to eat seedless watermelons. Answer the following
questions about making seedless watermelon
a. Seeds of a diploid variety called ‘Charleston Gray’ were treated with the chemical
colchicine. Some of the offspring of the plants derived from these seeds were tetraploid.
Cholchicine must…..
____interfere with DNA replication
____interfere with spindle fiber function
b. How many chromosomes are in the somatic cells of these tetraploids?________
Now these tetraploids are used as females and diploid ‘Sugar baby’ plants are used as
males in a cross.
c. How many chromosomes are in the somatic cells of the hybrids produced by the cross
described?
d. The offspring produced are…. ___ diploid ___ triploid ____ tetraploid
e. These offspring do not make viable seeds. Explain why.
f. What kind of cell division is occurring properly in these sterile offspring?__________
13. Triticale is a polyploid species that was produced intentionally by humans. Rye is a
diploid (2n = 14) and it was crossed with tetraploid wheat to produce a sterile hybrid.
a. How many chromosomes are in the somatic cells of this sterile hybrid?______
Treating the sterile hybrid with colchine allows for the formation of a few seeds that
could grow into a new fertile species (Triticale)
b. Triticale is a __autotetraploid
autohexaploid ____allohexaploid ___allohexplaoid
14. Two commercial Roundup Ready events are available in soybean.
a. Event X
on chromsome
#3?
Which is the best
Location for the
RR transgene in
soybean?
RR
more ovules/ovary
development
allele
b. Event Q
on chromosome
#13?
lower seed
weight allele
RR
Explain your choice.
15. a. Contrast a cross over with a translocation:
b. Contrast a translocation with a transgene: