Test 1, Fall 2007
Part One. Short Answers
Answer 5 of the following 6 questions completely in the space provided. You must show all work in order to
receive full credit for the question. Make sure to define all gene symbols, and to indicate allele dominance
relationships in your definitions.
Name___________________________________
1) An unaffected man whose father expresses a recessive trait marries an unaffected woman with a brother
expressing the same recessive trait. The man's mother, youger brother and sister are all unaffected. The
woman's parents are both unaffected.
a)
Draw the pedigree of this family in the space below, indicating all genotypes.
b) What is the probability that the newlyweds' first child will express the trait?
c)
What is the probability that the newlyweds will have two heterozygous children?
2) A true-breeding red snapdragon was crossed to a true-breeding white snapdragon. The F1 progeny were
red. When the F1 were selfed, the following F2 progeny were observed:
Total
1850 red
670 pink
831 white
3351
(a) Using your own clearly defined genetic symbols, give the appropriate parental, F1 ,and F2 genotypes in
order to explain the above results.
(b) What phenotypic ratio would be expected from a testcross of an F1 snapdragon?
(c) Suppose the white phenotype is now lethal. What phenotypic ratio would be expected from a cross
between F1 individuals?
3) The following coat colors are known to be determined by alleles at one locus in horses:
palomino
cremello
chestnut
= golden coat with lighter mane and tail
= almost white
= brown
The following table gives ratios obtained in matings of the above varieties:
Cross
1
2
3
Parents
cremello x cremello
chestnut x chestnut
cremello x chestnut
Offspring
all cremello
all chestnut
all palomino
4
palomino x palomino
1/4 = chestnut
1/2 = palomino
1/4 = cremello
Assign gene symbols for the genetic control of coat color on the basis of these data.
Diagram the last two matings, giving the genotypes of all individuals.
4) Normal diploid somatic (body) cells of the mosquito, Culex pipiens, contain six chromosomes (two copies
each of three chromosomes, that are designated by the capital letters A, B and C). Assign the symbols
,
, and
to the three homologous chromosomal pairs. The "m" superscript indicates that
the homologue is maternally derived, while the "p" indicates a paternally derived homologue.
(a) In each of the nuclei below, draw the expected configuration of all chromosomes, making sure to label
each homolog using the symbols defined above,
Mitotic Metaphase
Metaphase of Meiosis I
Metaphase of Meiosis II
(b) The stage at which "sister chromatids go to opposite poles" immediately follows which of the above
stage(s) (more than one answer can be correct)?
(c) Assuming that all nuclear DNA is restricted to chromosomes and that the amount of nuclear DNA
essentially doubles during the S phase of interphase, how much nuclear DNA would be present in each
nucleus listed above? Note: assume that the G1 nucleus (just prior to S phase) of a mosquito cell contains 3.0
X 10-12 grams of DNA.
5) In the house mouse coat color is genetically controlled. The results of a series of matings involving
yellow, tan, black and blackish-tan are shown. Give a complete genetic explanation of these results,
including the genotypes of all individuals.
Cross
Parents
Offspring
1
yellow x yellow
391 yellow : 132 black
2
tan x yellow
214 tan : 210 yellow
3
yellow x yellow
284 yellow : 108 tan
4
yellow x yellow
306 yellow: 110 blackish-tan
5
blackish-tan x blackish-tan
110 black: 210 blackish-tan:101 tan
6
blackish x tan
all blackish-tan
7
black x blackish-tan
141 black: 144 blackish-tan
6) Two plants are crossed; their genotypes are A/A;B/b;C/c and a/a;B/b;c/c. What
phenotypic ratio would be expected among the progeny of this cross, given the following
conditions: Assume that allele A codes for color with A being green and a being white; the B allele codes for pod size
with B being big and b being small; and allele C codes for wrinkled leaves with C being wrinkled and c being smooth.
a) All three genes display complete dominance.
b) All three genes display incomplete dominance, with the Aa, Bb and Cc phenotypes of pale green, medium, and
crinkled, respectively.
Part 2: All students must answer this question. You and your lab partner decide to test several members of
the Borden family, who are depicted in the pedigree below, for the presence of an RFLP associated with high
susceptibility to MODI-1 Type 2 Diabetes (the trait depicted in the pedigree). Each family member's DNA
was digested with Eco RI, run out on an agarose gel using standard procedures, and Southern blotted.
Finally, a DNA probe was used to assay for the presence or absence of a marker gene (A) known to be very
closely linked to the MODI-1 susceptibility gene. Answer all of the questions on the next page based on the
resulting data:
Figure 1. The Borden Family Pedigree
II-1 II-2 II-3 II-4 III-2 III-4 III-5 III-6 III-7
III-8
Figure 2. RFLP analysis of Borden family DNA. The
identity of each family member in the analysis is
indicated by the pedigree number above each well.
a) Is this trait inherited as a dominant or as a recessive allele? Explain
b) Is this trait autosomal or X-linked? Explain
c)
Write the genotypes of each family member on the pedigree above.
d) Which of the two molecular alleles - A' or A'' - is linked to the MODI-1 susceptibility allele? Explain.
e) What is an RFLP?
f) Individuals III-4 and III-5 come to you wanting to know what the probability is that their children will
carry the MODI-1 allele. What do you tell them? Make sure you address any issues involved in using
linked markers for genetic testing, rather than the gene itself.