Download Sample questions - I Exam

GENETICS (BIO S325)
SUMMER 2006
Sample questions - I Exam
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1.
Which of the following choices describes the most likely pattern of inheritance of
a trait shown in the given pedigree?
(a)
(b)
(c)
(d)
(e)
(f)
Autosomal dominant
Autosomal recessive
Cytoplasmic inheritance
X-linked recessive
Y-linked
X-linked dominant
2.
The mouse autosomal genes B and S are linked and 38 map units apart. Mice with
genotypes B S/B S and b s/b s are crossed and the F1 is testcrossed to b s/b s. The
proportion of mice with the genotype B-S- in the testcross progeny will be
3.
A dihybrid plant in trans conformation is testcrossed to a plant with the genotype
ab/ab. In 28% of the cells undergoing meiosis, no chiasmata is observed between
the linked genes A and B; in 72% of the cells, there is one chiasma between the
two genes. What proportion of the progeny from the cross will be ab/ab?
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4.
In a testcross of an individual, heterozygous for each of three linked genes, the
most frequent classes of progeny were A B c / a b c and a b C / a b c, and the least
frequent classes were A B C / a b c and a b c / a b c.
(a)
What is the genotype of the trihybrid?
(b)
5.
What is the order of the genes?
Imagine a diploid sexually reproducing organism, Diploidus sexualis, that
contains three pairs of chromosomes. This organism is unusual in that no
recombination between homologous chromosomes occurs during meiosis.
(a)
Assuming that the chromosomes are distributed independently during
meiosis, how many different types of sperm or egg cells can a single
individual of this species produce?
(b)
What is the likelihood that two siblings of this species will be genetically
identical?
6.
Indicate whether the following is TRUE for meiosis, mitosis, both, or neither.
(a)
Formation of a bivalent
(b)
Products are genetically identical
(c)
Chromosomes condense
(d)
All paternal chromosomes segregate to one cell
(e)
Involves DNA replication
7.
For each of the following sentences, fill in the blanks with the best word or phrase
selected from the list below. Not all words or phrases will be used; each word or
phrase should be used only once.
In eucaryotic __________________, DNA is complexed with proteins to
form __________________. The paternal and maternal copies of human
Chromosome 1 are __________________, whereas the paternal copy of
Chromosome 1 and the maternal copy of Chromosome 3 are
__________________. Cytogeneticists can determine large-scale
chromosomal abnormalities by looking at a patient’s karyotype. Fluorescent
molecules can be used to paint a chromosome by virtue of DNA
__________________, and thereby to identify each chromosome using
microscopy.
chromosomes
hybridization
extended
condensation
homologous
bands
kinetochore
nonhomologous
chromatin
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8.
A tall pea plant with axial flowers was crossed to a dwarf plant with
terminal flowers and the following offspring were obtained: 27 tall plants
with axial flowers; 23 tall plants with terminal flowers; 28 dwarf plants
with axial flowers; and 25 dwarf plants with terminal flowers. Tall plants
and axial flowers are dominant phenotypes. Using the symbols T and t for
plant height, and A and a for flower position, give the genotypes of the
two parents in this cross.
9.
A sex-linked recessive allele c produces a red-green colorblindness in humans. A
normal woman whose father was colorblind marries a colorblind man.
(a)
What genotypes are possible for the mother of the colorblind man?
(b)
10.
What are the chances that the first child from this marriage will be a
colorblind boy?
A couple discovers that they both had an uncle who died of Tay-Sachs disease.
What is the probability of their producing a child with Tay-Sachs disease?
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11.
In corn (Zea mays), the genetic map of part of chromosome 4 is as follows, where
w, s, and e represent recessive mutant alleles affecting the color and shape of the
pollen:
w
s
e
10 m.u
If the following cross is made
w+s+e+/w+s+e+
20 m.u.
x
wse/wse
and the F1 is testcrossed to wse/wse, and if it is assumed that there is no
interference in this region of the chromosome, the proportion of progeny with the
following genotypes will be:
12.
13.
(a)
w+s+e+/ wse
(b)
w+s e / wse
(c)
w+s+e/ wse
(d)
w+s e+/ wse
(a)
Explain why large recombination frequency values are less accurate
measures of map distance than smaller ones.
(b)
During an experiment involving two genes you determine that the
recombination frequency (RF) between the two genes is close to 50%.
What can you conclude about the linkage relationship of the two genes
that you are studying?
Genes a, b, and c are present on a single chromosome in the order given and the
distances between genes a and b are 20 map units and between b and c are 16 map
units. In a trihybird testcross, 16 double recombinants were obtained in a total of
1000 progeny. Calculate the interference observed in this cross.
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14.
A diploid plant has a chromosome content of 2n = 8. Diagrammed below are
individaul cells of a tetrahybrid plant (A/a; B/b; C/c; D/d). In each case mention
if the diagram represents a cell in mitosis, meiosis I, meiosis II, or not possible.
Each line represents a chromatid.
(a)
A
B
C
D
a
b
c
d
a
b
c
d
A
B
C
D
B
A
(b)
B
b
A
a
(c)
C
d
A
b
C
d
C
a
c
D
b
15.
d
c
b
B
(e)
d
A
A
(d)
D
C
c
b
a
D
C
d
A
a
B
b
C
c
D
d
A
a
B
b
C
c
D
d
In humans, males are the heterogametic sex with an X and Y chromosome in each
somatic cell. During the formation of gametes, each daughter cell receives either
an X or a Y chromosome. Considering that the X and Y chromosomes are
different in size and the genes that they carry, how do they pair during meiosis to
be segregated equally among daughter cells?
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16.
What are the progressive levels of packing of DNA in eukaryotic chromosomes?
Mention the major structure observed at each stage of packaging and where
known, the dimensions of the structure and the proteins involved in packing.
17.
Which ONE of the following statements is true with respect to haploid and diploid
life cycles?
(a) Meiosis is simpler in haploid organisms, owing to unpaired chromosomes.
(b) Zygotes differentiate directly into meiotic products in haploids without
intervening meiotic divisions.
(c) Somatic nuclei of haploids have the gametic chromosome number.
(d) Somatic nuclei of diploids have the gametic chromosome number.
(e) Somatic nuclei of haploids have the zygotic chromosome number.
18.
The human genome is comprised of 23 pairs of chromosomes found in nearly
every cell in the body. Answer the quantitative questions below by choosing one
of the numbers in the following list:
23
46
19.
69
92
(a)
How many centromeres are in each cell?
(b)
How many telomeres per cell?
(c)
How many replication origins per cell?
>200
>109
Evidence suggests that the replication of DNA packaged into heterochromatin
occurs later than the replication of other chromosomal DNA. What is the simplest
possible explanation for this phenomenon?
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20.
In humans, the ability to taste the chemical phenylthiocarbamide (PTC) is
attributed to the dominant allele of a gene, denoted T, located on chromosome 7.
The recessive allele of this gene is designated t. Individuals with the genotypes
T/T and T/t are tasters of PTC, and those with the genotype t/t are nontasters.
From 204 matings of heterozygous tasters with nontasters, 258 taster and 278
nontaster progeny were observed. Perform a chi-square test to determine if the
observed results fit the Mendelian expectation of equal segregation (1:1) of alleles
during the formation of gametes.
(a) Determine the chi-square value from the given data.
(b) What are the degrees of freedom in this example?
(c) Determine the approximate probability (P value) from the given table.
(d) Based on the P value, is the hypothesis accepted or rejected?
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