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Genetics, Fall 2001
TEST 2, 11/12/01
Page 1
STUDENT NAME: ___________________________
Give a brief definition of the following terms (5 points each; only seven definitions count for
the grade):
1.
phenotype
2.
heterozygous
3.
codominance
4.
kinetochore
5.
interphase
6.
testcross
7.
X-linked
8.
centimorgan
Genetics, Fall 2001
TEST 2, 11/12/01
Page 2
Give brief answers to the following problems (5 points each; only eight answers count for the
grade):
1.
Name the four phases of mitosis. Describe the behavior of the chromosomes in
each of these phases.
2.
Name the two processes in meiosis that contribute to the new combination of
maternal and paternal genetic material. At which stages of meiosis do they occur?
3.
Describe the dominance/recessiveness relationships of the alleles in the ABO blood
system in humans.
4.
The A and B antigens of the ABO blood system are synthesized by adding specific
sugars to an oligosaccharide, the H-antigen, on the surface of red blood cells.
Individuals with the “Bombay” blood phenotype (named after the place where this
phenotype was discovered first) do not express the H-antigen, due to a recessive
mutation in a gene involved in the synthesis of this antigen. The genotype of these
individuals can be described as h/h, where h is the recessive mutant allele (and H the
corresponding normal allele).
What is the ABO blood type of an individual with the genotype h/h, A/A? What is the
blood type of an H/H, O/O individual? What is the blood type of a child of these two
individuals? What is the genotype of the child?
Genetics, Fall 2001
TEST 2, 11/12/01
Page 3
5.
In a particular breeding experiment, the F1 generation of true-breeding parents was
found to be phenotypically uniform. Mating individuals of the F1 generation with each
other yielded an F2 with 3 different phenotypes. The numbers of individuals in the
three phenotypic classes were 40, 50, and 70, respectively. Name a possible mode of
inheritance that can explain this F2 data. Support your hypothesis by performing a χ2test. Show all your calculations and explain the basis of your decision to accept your
hypothesis! A χ2-table can be found in the appendix on page 7.
6.
True-breeding flies with vestigial wings (gene symbol: vg) were crossed with truebreeding flies with brown eyes (gene symbol: bw), in order to determine the genetic
map distance between these two genes located on Drosophila chromosome 2.
Testcrossing the uniform wildtype F1 generation yielded the following offspring: 312
flies with vestigial wings, 165 wildtype flies, 338 flies with brown eyes, and 185 flies
with vestigial wings and brown eyes.
Are the mutant alleles in the F1 flies in cis or trans configuration? What is the map
distance between the vestigial and the brown gene? Show the genotypic
representation of the testcross and your calculations!
Genetics, Fall 2001
7.
TEST 2, 11/12/01
Page 4
Below you see different combinations of sex chromosomes in individuals; the number of
autosomes is normal in each case. What is the sex of the individuals, if they were
humans, or if they were flies? How many Barr bodies would you see in the cells of
these individuals?
Sex
Chromosomes
Drosophila
Human
Sex
Barr bodies
Sex
Barr Bodies
X0
XX
XY
XXY
8.
Below you see two stages of nuclear division in an organism that has 6
chromosomes (2n = 6). Which stages are shown?
9.
Below you see the electrophoretic analysis of blood samples for the presence of a
particular protein. The father of the analyzed family is homozygous for the fast
running form of the protein (1), the mother is homozygous for the slow running form
(2). Lane 3 shows the result for a mixture of blood from the father and the mother, and
lane 4 shows the blood of their heterozygous daughter.
Is the functional form of the protein a monomer or a dimer?
In lane 5, add the expected protein pattern in a blood sample of the heterozygous
daughter, if the gene were located on the X-chromosome.
Genetics, Fall 2001
TEST 2, 11/12/01
Page 5
Write a short essay on one out of the following two topics (25 points):
1.
A cross between true-breeding sweet pea plants with red flowers (genotype B/B,R/R)
and white flowers (genotype b/b,r/r) yields a uniform F1 generation with red flowers.
Self-fertilization of the F1 plants results in an F2 generation with red and white flowers in
a ratio of 9:7. Develop a Punnett square for the F2 generation and describe the mode
of inheritance. Develop a molecular model to explain the ratio of the F2 phenotypes
using your knowledge in gene expression.
Genetics, Fall 2001
2.
TEST 2, 11/12/01
Page 6
According to the one-gene-one-enzyme hypothesis a gene is a part of the genome
that controls the production of an enzyme. Discuss how this hypothesis is still useful in
understanding the phenomenon of incomplete dominance as it occurs, for instance, in
the inheritance of flower color in four o’clock plants. Include a molecular model!
Discuss aspects of gene function which are not covered by the one-gene-oneenzyme concept.
Genetics, Fall 2001
Appendix: χ2-Table
TEST 2, 11/12/01
Page 7