Genetics as it applies to evolution, molecular biology, and medical aspects.

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Post by chousta » Sat Aug 23, 2008 7:14 am


just afew revision questions i need help with because i dont have any answers. in bold are my answers

1) Sex linkage of a gene
a) means that the phenotype is confined to one sex
b) involves only the Y chromosome
c) implies that the gene is on one of the sex chromosomes
d) means that colour blindness occurs only in women
e) is another term for sex limited


2) Loci A and B are unlinked. Two double heterozygotes are crossed. The proportion of
offspring with genotype Aa Bb is expected to be:
a) 1/2
b) 3/16
c) 1/4
d) 9/16
e) 1/6


3) Two genes are located 10 map units apart. The proportion of genotype AB/AB
individuals from a cross between two AB/ab individuals is
a) 0.2025
b) 0.1625
c) 0.768
d) 0.2125
e) 0.45

B, not sure though!

4) The recombination value is given by the ratio of numbers of
a) parentals /recombinants
b) recombinants /parentals
c) parentals / total
d) total / parentals
e) none of the above

E...isnt it recombinants/total?

5) An individual is heterozygous at two loci: A/a and B/b. This individual is test crossed
and 100 progeny from the test-cross are scored. Of these 42 show the phenotype AB, 38
show the phenotype ab and 11 show the phenotype aB.
The most likely map distance between the loci A/a and B/b is
a) 80 mu
b) 40 mu
c) 22 mu
d) 20 mu
e) 11 mu


6) A female fly of unknown genotype has long antennae and clear wings. These phenotypes
are dominant over short antennae and grey wings. The female is mated to a male with
short antennae and grey wings, and 200 offspring are produced. All of them have long
antennae and clear wings. What is the genotype of the female fly?
a) ss gg
b) Ss Gg
c) SS Gg
d) Ss GG
e) SS GG


7) A single plate of E. coli was replicated onto several plates which were later treated with
T1 phage. These plates grew phage resistant colonies appearing in the same position on
each replica plate. This indicates that :
a) the contact with T1 phage induces change that produces resistance.
b) T1 phage can mutate to a virulent form.
c) the mutations must have occurred after contact with T1 phage
d) the resistance to T1 phage pre-existed in the cultures.
e) mutation to T1 resistance is common.

D, because they showed up in in both plates and same places, it already has resistance. if they appeared on one plate and not the other then its a different story?

Cool Which of the following statements about gene mapping are TRUE
a) Hfr strains are useful for mapping genes which are separated by 1 min or less on the E. coli
b) Transduction is useful for determing the relative order of genes on the E. coli chromosome
that are separated by not more than 1 min.
c) Hfr conjugation and P1 transduction can only be used when the yeast strains are haploids
(i.e. not with diploids).
d) None of the above

9) Conjugation was performed with the following donor and recipient strains:
Donor: Hfr, thi, pro
Recipient: F-, thi, leu, arg, rpsL
Which of the following media would enable the selection of an arg+ exconjugant?
a) glucose, thiamine, arginine, streptomycin
b) glucose, thiamine, leucine, streptomycin
c) glucose, thiamine, proline
d) glucose, thiamine, leucine, arginine, streptomycin
e) glucose, thiamine, leucine, arginine, proline

no idea!

10) The F2 generation of a dihybrid cross between green-seeded, tall and yellow-seeded
dwarf pea plants produced offspring in the following numbers.
Green-seeded, tall 47 …………3
Yellow-seeded, dwarf 70 …………3
Green-seeded, dwarf 7 …………1
Yellow-seeded, tall 196 …………9
a) On the dotted lines above, write the expected numbers of each class if Mendel’s laws of
segregation and assortment hold.

b) Which alleles are dominant and which are recessive at the two loci?
dominant: tall, yellow
recessive:dwarf, green

c) Are alleles at each of the seed colour loci segregating normally? The 5% critical values
of the Chi-squared distribution are:
d.f. 1 2 3 4 5 6
χ2 3.84 5.99 7.82 9.49 11.07 12.59

no calculator but can do..

x^2=sigma (observed-expected)^2/epected


Posts: 38
Joined: Tue May 13, 2008 7:49 pm

Post by MisterATP » Sat Aug 23, 2008 5:08 pm

1. c)
2. d)
3. I don't understand question. ''genotype AB/AB'' <----- What does it mean?
4. I think you're right.
5. Right, but I don't like some interpretations (like phenotype aB) or slashes.
6. e) You don't need the meaning of symbols. Just try to remember when all offspring are the same phenotype when one parient is with dominant phenotype and other is with recessive.
7. I guess it is right.
8. I am not sure of other, but a) I think is right. I doubt just for time...
9. c) Exconjugant will have arg gene (arg+), so it no more needs arginine in the media. But as you see in b media isn't arginine also, but streptomycin is. Exconjugant hasn't gene of resistance for this antibiotic so it would die and no selection occured.
10. You can do this...;)

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