Genetics

1
INTERACTIVE MULTIPLE CHOICE QUESTIONS
Genetics
The answers are provided. Explanations of why the
alternatives are unsatisfactory are also offered
2
These multiple choice questions are similar to
the ones set by the GCSE and IGCSE Examination
Boards except that, in some cases, there may be
more than one acceptable answer
For this reason, even if you select a correct
answer at your first attempt, it is worth looking
at all the alternatives (a)
to see if there is a better answer and
(b) to see
why some of the alternatives are unacceptable
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Question 1
A fathers blood group is AB the mothers is
O. Which of the following blood groups could
appear in their offspring?
4
Yes
The fathers genome must be iAiB The mothers
genome will be iOiO
The combination iAiO is possible and will be
expressed as group A because iA is the dominant
allele
5
Yes
The fathers genome must be iAiB The mothers
genome will be iOiO
The combination iBiO is possible and will be
expressed as group B because iB is the dominant
allele
6
No
The fathers genome must be iAiB The mothers
genome will be iOiO
The offspring will all inherit either iA or iB
from their father and iO from their mother. Their
genomes will be either iAiO (expressed as group
A) or iBiO (expressed as Group B. Group AB is
not possible
7
No
The fathers genome must be iAiB The mothers
genome will be iOiO
The offspring will all inherit either iA or iB
from their father and iO from their mother. Their
genomes will be either iAiO or iBiO. The alleles
iA and iB are both dominant to iO so group O is
not possible
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Question 2
A pure-breeding male black mouse is mated with a
female brown mouse and they produce a litter of
12. The allele for black fur is dominant to the
allele to brown fur.
What is the expected distribution of colour and
sex in their litter?
9
No
The pure-breeding males genome must be BB and
the brown mouses genome must be bb. The allele
for black fur is dominant over the brown allele.
Therefore all the offspring will be black (Bb)
gametes
Black male
Brown female
B
B
b
Bb
Bb
b
bB
bB
10
No
As explained in the previous slide, the allele
for black fur is dominant to the brown allele, so
there can be no brown mice in the litter from
this cross
11
Yes
Inheritance of colour is explained in the first
answer. The male mouse carries the X and Y
chromosomes. The female mouse carries two X
chromosomes. At meiosis, only one of each
chromosome pair goes to the gametes.
gametes
Black male
Brown female
BX
BY
bX
BbXX
BbXY
bX
bBXX
bBXY
12
No
Certainly all 12 mice will be black as explained
in the first answer, but the sex is inherited as
explained in the third answer, so the expectation
is that there will be 6 males and 6 females in
the litter
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Question 3
A male heterozygous black mouse (Bb) is mated
with a female heterozygous black mouse (Bb) and
the litter consists of 12 pups. B is the allele
for the black colour. The allele for brown colour
is b. The dominant allele is B.
Which of these ratios is closest to the
expected ratio for the distribution of colour
among the offspring?
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Not very close
From the Punned square you can see that the
expected ratio is 3 black (BB or Bb) to 1 brown
(bb)
B
b
gametes
BB
Bb
B
b
Bb
bb
These are only the chance combinations. It would
be possible to produce 12 black pups, since
black is the dominant allele but this is not
close to the expected ratio
15
Not very close
From the Punnett square you can see that the
expected ratio is 3 black (BB or Bb) to 1 brown
(bb)
B
b
gametes
BB
Bb
B
b
Bb
bb
These are only the chance combinations. It would
be possible to produce 6 black and 6 brown pups
but this is not very close to the expected ratio
of 93
16
Close but
From the Punnett square you can see that the
expected ratio is 3 black (BB or Bb) to 1 brown
(bb)
B
b
gametes
BB
Bb
B
b
Bb
bb
These are only the chance combinations.
A combination of 4 black to 8
brown is close to the expected ratio of 39 but
since black is the dominant allele it seems to be
the wrong way round
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The closest
From the Punnett square you can see that the
expected ratio is 3 black (BB or Bb) to 1 brown
(bb)
B
b
gametes
BB
Bb
B
b
Bb
bb
These are only the chance combinations.
A combination of 8 black
to 4 brown is closest to the expected ratio of 93
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Question 4
The diagrams represent stages in cell division by
mitosis. (only one chromosome is represented).
What is the correct sequence of events?
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No
The chromosomes shorten and thicken (b) after
they have appeared in the nucleus (b). Similarly
at the end of cell division, the chromosomes
extend and become less visible (d) after the cell
divides (e)
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Yes
This is the correct sequence
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No
The cell does not start to divide (d) until the
chromatids have separated (c). Also, cell
constriction (e) precedes cell division (d)
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No
Cell division (d) does not take place until the
chromatids have appeared (b) and separated (c).
Also, cell constriction (e) precedes cell
division (d)
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Question 5
The process of cell division by meiosis takes
place only
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No
Although the cells in the basal layer of skin
divide rapidly, it is by mitosis
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No
Cells in the red bone marrow divide rapidly to
produce red and white blood cells, but this is by
mitosis
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Yes
The cells in the reproductive organs which
produce gametes will undergo a meiotic division
and produce haploid gametes
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No
The lymphocytes are capable of dividing rapidly
to produce clones of cells but this involves only
mitosis
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Question 6
In a DNA molecule, which of the molecules listed
below pairs with adenine?
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Yes
30
No
Guanine pairs with cytosine
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No
Valine is an amino acid and not an organic base
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No
Cytosine pairs with guanine
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Question 7
If L is the allele for long hair and l is the
allele for short hair, B is the allele for
black hair and b is the allele for white hair,
S is the allele for straight hair and s is the
allele for curly hair
What will be the phenotype for a small dog with
the genotype LLBbss?
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No
The allele for black fur is dominant to the
allele for white fur
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No
The dog carries both dominant alleles for long
hair
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No
The dog is heterozygous for the colour gene, but
the allele for black fur is dominant to the
allele for white fur
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Yes
The dog is homozygous recessive for the curly
allele, homozygous dominant for hair length and
heterozygous for the colour gene but the black
allele is dominant
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Question 8
Bacteria can be genetically modified to produce
human insulin. The steps involve
(a) cutting out the insulin gene from human DNA
with restriction enzymes,
(b) extracting plasmids from the bacterium,
(c) returning the modified plasmid to the
bacterium,
(d) inserting the insulin gene into the plasmid,
(e) cutting open the plasmid with the same
restriction enzyme
Which of the following is the correct sequence?
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No
The plasmids cannot be cut open (e) until they
are extracted from the bacterium (b)
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No
The insulin gene must be inserted in the plasmid
(d) before it is returned to the bacterium (c)
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Yes
This is the correct sequence b, a, e, d, c would
also be acceptable because the restriction enzyme
can cut the plasmid DNA and human DNA in any order
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No
The plasmid DNA must be opened (e) before the
insulin gene can be inserted (d)
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Question 9
Before natural selection can take place in an
animal, there has to be either
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Yes
A gene mutation which caused a change in the
organism could be subject to natural selection
45
No
A change of habitat might favour a variation
resulting from a genetic change, such as a
mutation, but selection could not result from an
organism simply changing its habitat
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Yes
A new combination of genes could produce a
variation that had a selective advantage
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No
A climate change might favour some variants in a
population but could not, itself, produce those
variants. There has to be a genetic change for
the climate change to act upon
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Question 10
Which of the following can be inherited?
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Yes
Cystic fibrosis is caused by a gene mutation. The
gene controls the movement of salts and water
into and out of the cells. The mutated form of
the gene causes thick mucus to be secreted by the
lungs, airways and pancreas, plus many other
symptoms.
The mutated gene is
recessive to the normal gene..

50
No
AIDS is caused by a virus, the human
immunodeficiency virus (HIV). The virus is
transmitted by sexual intercourse or by infected
syringe needles.
An infected mother may pass the disease on to her
baby, so the disease may, superficially, appear
to be inherited
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Yes
Sickle cell anaemia is caused by a mutation in a
gene controlling the composition of haemoglobin.
This mutation causes the red cells to become
distorted in low oxygen concentrations and so
block small blood vessels. The
mutated gene is recessive to the normal gene
52
No
Tuberculosis is an infectious disease caused by a
bacterium Mycobacterium tuberculosis. The
bacteria are carried in the air.
In
most cases, the disease affects the lungs.
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End of questions
End show