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GENETICS 310
EXAM III
April 26, 2011
I. A plant heterozygous for genes D and H that are 20 map units apart is self-pollinated.
A) Give the genotypes of the plant if it is in:
D 20 H/d
1) coupling
h
2) repulsion D
20
h/d
H
B) Give the expected frequencies of the gametes for each case.
1) coupling
2) repulsion
DH
Dh
dH
dh
40%
10%
10%
40%
DH
Dh
dH
dh
10%
40%
40%
10%
C) Give the expected frequency of double homozygous recessives in the progeny expected in
each case:
1) coupling 0.4 X0.4 = 16%
2) repulsion 0.1 X 0.1 = 1%
II. Check all correct responses for each syndrome listed:
Turner: # of chromosomes: 45 x
46 47
sex: M
Fertile: Y
N x
Height: tall
Klinefelter: # of chromosomes: 45
Fertile: Y
N x
46
47 x
Height: tall x short
Jacob: # of chromosomes: 45
Fertile: Y x
short x
N
46
47 x
Fertile: Y x N
Height: tall
46
1 x
2
47 x
short
Fertile: Y
sex: M x
N x
1
2 x 3
female
F x
# of X’s: 0
1
46 x 47
47 XX +21
# of Y’s: 0
1 x 2
1
1 x 2
1
3 x
sex: M
1 x 2
2 x
3
# of Y’s: 0 x 1
2
2
3
# of Y’s: 0
Write the standard karyotypic designation for a “Downs” syndrome
Male 47 XY +21
2
F
sex: M
# of X’s: 0
# of Y’s: 0 x
1 x
sex: M x F
# of X’s: 0
Testicular feminization: # of chromosomes: 45
# of Y’s: 0
# of X’s: 0
# of X’s: 0
Height: tall x short
TriploX: # of chromosomes: 45
F x
F x
3
2
III. A) Recalling that in birds the female is the heterogametic sex and knowing that barred
feathers is a sex-linked recessive gene on the Z chromosome, show the genotypes of the parents
and predict the ratios (include sex) in the following crosses:
Barred female by homozygous plain male: ZbW female X ZBZB male
All female progeny are ZBW (plain) and all males are ZBZb (plain)
Plain female by barred male: ZBW female X ZbZb male
All female progeny are ZbW (barred) and all males are ZBZb (plain)
Plain female by heterozygous male: ZBW female by ZBZb male
Progeny 1 ZBZB : 1 ZBZb male, both plain : 1ZBW female (plain) : 1 ZbW female (barred)
B) Mahogany in Ayrshire cattle is dominant over red in males but recessive in females. What
term describes this pattern of inheritance?
Sex-influenced
Give a legend to show how red/mahogany coat is inherited and show the genotypes of the
parents of the crosses indicated below.
Legend:
Genotype
Females
Bulls
M”M”
Mahogany
Mahogony
M” M
Red
Mahogany
MM
Red
Red
Cross 1. red ♀♀ by mahogany ♂♂  3 red ♀: 1 mahogany ♀: 3 mahogany ♂: 1 red ♂
Genotype of: cows
M”M
bulls
M”M
Cross 2. red ♀♀ by mahogany ♂♂  all ♀ calves red, all ♂ calves mahogany
Genotype of: cows
MM
bulls
M”M”
C. A plant with male sterile cytoplasm [S] is male fertile if a dominant restorer nuclear gene (Rf)
is present, whereas fertile [F] cytoplasm does not need the restorer. Predict the male fertility of
the progeny taken from the female in the following crosses:
a) [S] rf/rf ♀ X [S] Rf/Rf ♂ ALL MALE FERTILE
b) [S] rf/rf ♀ X [S] Rf/rf ♂ ½ MALE FERTILE
c) [S] rf/rf ♀ X [F] rf/rf ♂
ALL MALE STERILE
d) Is there a risk if all next generation seed is produced from these females? Explain.
Yes, since all have the exact same cytoplasmic genes, they could all be susceptible to the
same disease as happened in corn
IV. RFLP analysis of a mother heterozygous for hemophilia, her normal husband, two normal
daughters and an in-utero male fetus gave the following pattern (size controls not shown).
Dad Mom Daughter 1
Daughter 2
male fetus
Show the hemophilia
genotypes below each
individual.
XHY
XHXh
XHXH
XHXh
XhY
V. Using O for oncogene, T for tumor suppressor, R for retrovirus and D for DNA repair, tell
which is/are associated with the following:
T
Retinoblastoma
D
Xeroderma pigmentosum
D
R, O
Chicken sarcomas
O
turn on cell division
R
p53
HIV
VI. True or false
F Humans have more DNA per genome than all other species
F
The C-value paradox questions why organisms have different numbers of chromosomes
F DNA in eukaryotic chromosomes is wrapped around balls of histone proteins
T The DNA in human mitochondria does not attach to histones
T Mammalian DNA includes non-coding highly repeated sequences
F Mitochondrial DNA codes for all proteins found in the organelle
VII. Calculate the gene frequencies for the following populations:
a) A cell surface antigen is inherited in a codominant form. Of 1,000 persons tested, 40 were A'A',
320 were A'A and 640 were AA.
F(A) = (640 x 2 + 320)/ 2000 = 1600/2000 = 0.8
F(A’) = (40 X 2 + 320 )/ 2000 = 400/2000 = 0.2
F(A) =
0.8
F(A') =
0.2
b) In some parts of Africa, 4% of the children are born with sickle cell anemia. What is your best
estimate of the frequency of:
sq rt of
4/100 = 2/10
the Hb-S allele?
0.2
the Hb-A allele?
0.8
the % heterozygotes 32
What assumption was used to make these calculations?
Random mating
VIII. Check the boxes as appropriate for the following fetures/aberrations:
Feature/effect
Alternate versus adjacent segregation affects
fertility of heterozygotes
Deletion
Duplication Inversion Translocation
X
X
X
Not generally a problem if homozygous
Meisois I configuration
X
X
X
X
X
Contributes to evolution of genes or species
X
May be para- or pericentric
X
Can lead to high frequencies of trisomy 21
Homozygotes likely to show phenotypic
effect
X
X
Can effect male fertility more than female
Meisois I configuration
X
X
IX. Short answer questions
1) If a normal rice leaf cell has 24 chromosomes, how many would be found in a plant that is a:
Triploid? 36
2)What does PCR stand for?
Trisomic 25
Tetraploid
48
Polymerase Chain Reaction
3) Why is it easier to diagnose sickle-cell anemia in fetal cell samples than cystic fibrosis?
All SCA cases have the same single base change in their DNA which changes a restriction site;
in CF, there are many different changes in a very large gene to contend with.
4) Using the letters A and B to represent whole genomes, show the difference between an
autopolyploid and an allopolyploid: auto
AAAA
allo
AABB
5) Give an example of a plant that is propagated as a triploid
banana
.
6) Give an example of a trinucleotide repeat genetic disease
Huntingtons
7) What technique is used to produce DNA fingerprints? RFLP, Southern Hybrid or VNTRs
8) What is a Barr body?
Condensed, inactivated X chromosome
9) An example of a disease resulting from faulty genomic imprinting is?
Prader -Willi
10) What ‘forces’ can change gene frequency? Migration, mutation, drift and selection