BL414 Genetics Spring 2006
Test 1 Key
February 8, 2006
150 pts. total, 15% of final grade
1) (2.5pts.) T or F: In the nineteenth century (1800’s), an ingenious monk
named Gregor Mendel figured out that genes are made up of doublehelical DNA.
False
2) (2.5pts.) T or F: A single gene may have effects on seemingly unrelated
traits in an organism such as pigmentation and amino acid metabolism.
True
3) (2.5pts.) T or F: Mid-twentieth century experiments involving the transfer
of genetic material into and out of bacteria and viruses gave firm evidence
that genes are comprised exclusively of DNA.
True
4) (2.5pts.) Name the process by which proteins are created according to a
sequence encoded on messenger RNA.___translation______
5) (2.5pts.) What organelle carries out this process?____ribosome ____
6) (2.5pts.) What specialized molecules act as linkers between amino acids
and the three-letter genetic code on the mRNA?____tRNA__________
7) (5pts.) What is the term for the complete set of proteins expressed in a
particular cell or organism?_______proteome___________
8) (2.5pts.) You are a human geneticist studying the gene for the human
disease PKU. You need to amplify DNA in the PKU gene locus from a
patient’s blood sample. What procedure would you use?
___PCR (polymerase chain reaction)_______
9) (2.5pts.) You need to insert the DNA sequence from your patient into a
bacterial plasmid. What enzymes would be useful for cutting the DNA?
_____restriction endonucleases or restriction enzymes_______
10) (10pts.) Describe the two ways in which a mutation affects the proper
functioning of a gene.
a) Loss of function: the protein is not expressed or is nonfunctional
b) Gain of function: the protein is overexpressed or expressed in a
dysfunctional form that negatively affects cellular processes
11) (5pts.) Male and female black Labrador retrievers are mated. Although the
allele for black coat color is dominant, the gene for yellow coat color is at a
different genetic locus. Of the resulting puppies, there are 20 with a black
coat, 5 with a yellow coat, and 3 with a chocolate coat. What is the term for
the gene interaction that produces the color distribution seen in this litter
of puppies?___________epistasis__________
12) (5pts.) A scientist has isolated new 26 mutations disrupting wing
development in fruit flies. He finds that 12 belong to one
complementation group and 14 belong to another complementation
group. How many genes has he discovered?______two___________
13) (5pts.) A C. elegans cell containing 12 chromosomes goes through meiosis.
How many chromosomes does each resulting daughter cell
have?____six_______
14) During what phase of meiosis does the structure shown below occur?
(5pts.) _____prophase I_________
 (5pts.) What is the name for the structure shown below?
_____bivalent_________
 (15pts.) Label A, B and C (5pts.each).
A: centromere, B: chromatid, C: chiasma
15) (10pts.) What stage are the cells shown below in? (5pts. each)
a._____metaphase_________
b._______anaphase_______
16) (5pts.) How does meiosis account for the principle of independent
assortment discovered by Mendel? Explain.
“Genes on different chromosomes undergo independent
assortment because nonhomologous chromosomes align at
random on the metaphase plate in meiosis I. “
17) (35pts.) The following chart shows the results of different matings
between gourd plants that had either yellow or white flowers or either
smooth or bumpy gourds. The gourd plant is diploid.
Parent phenotypes
a)
b)
c)
d)
e)
Yellow smooth x yellow smooth
Yellow smooth x white smooth
Yellow bumpy x yellow bumpy
White smooth x white smooth
Yellow smooth x yellow bumpy
Yellow
smooth
94
89
0
0
40
Offspring phenotypes
White
Yellow
White
smooth bumpy bumpy
32
28
11
92
31
27
0
36
11
45
0
16
0
38
0
 (5pts.) Determine the dominant trait, or allele, for each gene.
Yellow and smooth
 (30 pts. plus bonus) Indicate the genotypes of both of the parents for
each of the different crosses below: (Decide on a letter to represent
each gene – put the gene for yellow vs. white flowers first.)
a) (7.5pts.)Yellow smooth
YySs
x
x
yellow smooth
YySs
b) (7.5pts.)Yellow smooth
YySs
x
x
white smooth
yySs
c) (7.5pts.)Yellow bumpy
Yyss
x
x
yellow bumpy
Yyss
d) (7.5pts.)White smooth
yySs
x
x
white smooth
yySs
e) (Bonus- 10 pts.) Yellow smooth
YYSs
Or
YySs
Or
YYSs
x
x
x
x
yellow bumpy
Yyss
YYss
YYss
19) (25pts. plus bonus) The pedigree below shows individuals who are affected with MRMC
syndrome, a disease that causes mental retardation and diminished motor control with an
average age of onset at 3 years.
I.
1.
2.
II.
2.
1.
III.
1.
3.
2.
4.
3.
4.
5.
5.
6.
7.
a) (5pts.) What is the mode of transmission of the MRMC gene? (Recessive or
dominant)?____recessive_____
b) (5pts.) Does this disease gene appear to be sex-linked or autosomal?
___sex-linked____
c) (5pts.) Which individuals in the pedigree are definitely carriers of the MRMC gene?
(You can mark them directly on the pedigree or list them here.)
I-1 and II-4
d) (10pts.) What is the probability that individual III-3 is a carrier of the MRMC gene?
½ or 50% because she has a ½ chance of receiving the recessive allele from her
mother who is a carrier and therefore heterozygous. She cannot receive the
recessive allele from her father because he does not have it – since the gene is
X-linked and he is not affected, his copy of the gene must be the normal allele.
e) (Bonus - 10pts.) What is the probability that individual III-3 will give birth to a child
who will be affected with the disease? (Assume that her mate has no family history
of the disease.)
3 events must occur to have the outcome of a child that is affected:
a) III-3 must be a carrier (1/2 or 50% chance)
b) Her child is a boy (1/2 or 50% chance)
c) The child receives the recessive allele from his mother who is
heterozygous (1/2 or 50% chance)
All three events have to occur for the given outcome so we multiply the chances for the
individual events together:
½ * ½ * ½ = 1/8 or 0.125 or 12.5% chance