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Winter 2015 – BIO207H5S – Pre-Tutorial Quizzes 6 to 8 (with Answers)
Pre-Tutorial Quiz #6:
1.) An individual has the following pair of homologous chromosomes (the ‘*’ represent the centromeres):
E F G H * I J K L M//e f g h * i l k j m. What kind of chromosomal abnormality is present in this individual?
d.) Pericentric Inversion
e.) Paracentric Inversion
2.) Suppose you decided to create a genetic cross by using the individual with the abnormal chromosome pair
from Question 1 and testcrossing to an individual with two normal homologs (i.e., both homologs are in
alphabetical order) resulting in 100 viable offspring. If K and J are 20 map units apart, how many of the viable
offspring (with no deletions or duplications) will be kkjj?
f.) ALL of the offspring.
3.) You have four Drosophila lines, each carrying a deletion (1 – 4 shown below) in a different area on one copy
of chromosome 2. The other copy (the normal chromosome with no deletions) of chromosome 2 contains
only mutant alleles with recessive phenotypes. Remember, these deletions are only found on one
homologue. The other homologue contains mutant alleles with recessive phenotypes for the genes found
in the area of the deletion:
alleles a, b, c, d, and e are known to be in the region of the
deletions, but their order is unknown. When the Drosophila
carrying the deletions are phenotypically analyzed, the following
results are obtained (summarized in the table below). In this
table, a minus means the deletion is missing the corresponding WT allele (i.e., the deletion uncovers the
recessive phenotype), and a plus sign indicates that the corresponding WT allele is still present. Use these
data to determine the order of the genes.
4.) In Drosophila, vestigial (partly formed) wings (vg) are recessive to normal long wings (vg+), and the gene for
this trait is autosomal. The gene for the white eye trait (w) is on the X chromosome (red eyes are w+). You
decide to setup a genetic cross and produce an F1 generation by crossing a homozygous white-eyed, long-
winged female fly to a homozygous red-eyed, vestigial-winged male. To continue with the experiment, you
set-up a second cross using two of the F1 flies. Suppose you select an F1 female that undergoes non-
disjunction of the sex chromosomes in meiosis I when producing her all eggs and cross her to an F1 male.
What would be the observed phenotypic ratio of the F2 females?
a.) ½ red-eyed, long winged: ½ red-eyed, vestigial winged.
b.) 3/8 white-eyed, long winged: 1/8 red-eyed, vestigial winged.
c.) 3/8 red-eyed, long winged: 1/8 red-eyed, vestigial winged.
d.) 9/16 white-eyed, vestigial winged: 7/16 red-eyed, long-winged.
e.) ¼ white-eyed, vestigial winged: ½ white-eyed, long-winged: ¼ red-eyed, vestigial winged.
5.) An alien organism has sex chromosomes similar to humans (XX = normal female, XY = normal male). A
particular male with the abnormal karyotype XYY mates with a normal XX female. If the probability of non-
disjunction of the X-chromosomes in the normal female is 2% during meiosis I and 3% during meiosis II, what
is the probability that this couple will have a child with the normal complement of sex chromosomes?
Assume that non-disjunction CANNOT happen during both MI and MII of a single meiosis event. Assume
normal segregation of the Y chromosomes during gametogenesis in the male (i.e., the Y’s get split up).
Assume that all sex chromosome combinations in the offspring are viable.
Pre-Tutorial Quiz #7:
1.) In a certain plant, leaf size is determined by four independently assorting genes acting additively. Alleles D,
E, F, G each add 4cm to leaf length and alleles D’, E’, F’ and G’ each adds 2cm to the leaf length. Suppose you
decide to cross a pure-breeding plant with leaves 32cm in length to a pure-breeding plant with leaves 16cm
in length. What is the observed length of the leaves in F1 plants?
2.) Let’s suppose you testcross an F1 plant (from Question 1). What proportion of the F2 plants will have leaves
16cm in length?