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Human Molecular Genetics
Assignment 2 (Week 2) with Answers
Q1. Identify the mode of inheritance of the phenotype in this pedigree
a. Autosomal recessive
b. autosomal dominant
c. X-linked recessive
d. X-linked dominant
Answer: B
Dominant because the disease manifests in all generations and autosomal because both male
& females are affected
Q2: Identify the mode of inheritance of the phenotype in this pedigree
a. Autosomal recessive
b. autosomal dominant
c. X-linked recessive
d. X-linked dominant
Answer: A, autosomal recessive
Autosomal because both male & female are affected and recessive because the disease does
not manifest in all generations – normally affected’s parents are unaffected as they are likely
to be carrier. However a marriage between two affected individuals results in the segregation
of the recessive alleles to all in the next generation and hence all their children are affected.
Q3: Based on the genotype given for the individual II-3, what would be her phenotype?
Assume it is a late onset phenotype.
a. She will develop the phenotype as she ages.
b. She is a carrier, and will not develop the phenotype
c. She is homozygous for the wild-type allele, and hence she will not develop the phenotype
d. The genotype given is not informative enough to conclude the risk.
Answer: c – will remain unaffected
The disease results from a mutation of on the gene A and not B. Hence II-3 which does not
contain the allele for A gene is normal
Q4: What two enzymes are needed to produce recombinant DNA?
a. endonuclease, transcriptase
b. DNA polymerase, topoisomerase
c. transcriptase, ligase
d. restriction enzyme, ligase
Answer: d
Restriction enzyme is required to create sticky or blunt complementary ends for the insert and
vector which then H-bond and their ends are sealed together by creating a phosphodiester
bond using the enzyme ligase
Q5. If a circular piece of DNA has three sites for a particular restriction enzyme, into how
many fragments will that restriction enzyme cut the DNA?
a. 3
b. 4
c. 5
d. 6
Answer: a
Q6: Shown below is the DNA finger printing pattern obtained for the DNA extracted from a
mother, her child, and the two males, each one claiming to be the biological father of the
child. Based on your understanding on the principles of DNA finger printing, identify the
person who is NOT likely to be the biological father of the child.
a. Male 1
b. Male 2
c. Neither of them can be the biological father of the child
d. The DNA profile is not good enough to predict the biological father
Answer: B
The DNA fingerprinting profile shows bands for highly repetitive regions of the genome.
Since every individual inherits one copy of these repeats from father and one from mother,
the similarity in inheritance pattern between the child and claiming fathers is being analyzed.
Here, every band of the child that is missing in the mother’s profile could be matched to a
band of the Male1, but not to Male 2. Therefore Male 2 does not seem to be the biological
father of the child.
Q7. Read the following steps and answer the question given below:
I. Transform bacteria with recombinant DNA molecule
II. Cut the plasmid DNA vector using restriction enzymes
III. Extract plasmid DNA vector from bacterial cells
IV. Hydrogen-bond the plasmid DNA vector to non-plasmid DNA fragment
V. Use ligase to join plasmid DNA vector to the non-plasmid DNA
From the list above, which of the following is the most logical sequence of steps for making a
recombinant DNA, that is inserting a foreign DNA into a plasmid vector and then introducing
the plasmid into a bacterium?
a. IV, V, I, II, III
b. III, II, IV, V, I
c. III, IV, V, I, II
d. II, III, V, IV, I
Answer: b
Self explanatory.
Q8: The following pedigree concerns the autosomal recessive disease known as Lafora
disease (LD). The couple marked “A” and “B” are planning to have a baby but are concerned
about the baby having LD. What is the probability of the first child having LD?
a. 0
b. 1/4
c. 1/12
d. 1/16
Answer: c, 1/12
Only when both A &B are carriers for the disease causing gene, their child would manifest
the disease since LD is autosomal recessive. The chance of A being a carrier is 2/3. Chance
of B being carrier is 1/2. And chance of their child being homozygous recessive is 1/4. Hence
2/3 x ½ x 1/4 = 1/12, as shown above. Thus there is 1/12 chance of the child having LD
Q9: The Auro (cast: Amitabh) character in the movie Paa was affected with a dominant
genetic disorder known as Hutchinson-Gilford Progeria Syndrome. Though it is a genetic
disorder, thus caused by a gene defect, neither the father nor the mother (cast: Abhishek and
Vidya respectively) of Auro was affected with this disorder. Their family had no previous
history of this disorder either. Which one of the following statements could most likely
explain this phenomenon? Assume none other than Auro developed progeria in the family.
a. It is a dominant disorder; though one of Auro’s parents carried the defective gene, he/she
did not develop the disorder.
b. It is a recessive disorder; however the affected should receive the defective gene from both
parents; thus both parents were heterozygous carrier yet did not show the phenotype.
c. The cause could be a germ line mutation, meaning, one of the germ cells of the one of the
parents had a defect in the gene
d. The germ-line specific mutation should have come from the mother, since sperms do not
transmit mutant genes.
Answer: c: germ line de novo mutation
Although Progeria is a dominant disorder, neither of the parents is affected. This could be due
to a mutation occurring in their gametes at the time of division.
Q10: A pedigree is shown below involving seven different alleles at an RFLP locus. The
electrophoretic gel shows the distinctive positions of eight fragments (1-8). The genotype
(RFLP pattern) for the parents in the second generation (II-1 and II-2) is masked. Which
alleles should each of the parents (II-1 and II-2) have on the basis of the grandparents’ and
children’s genotypes? Father: _____________ / Mother: _____________
a. 2, 5 / 3, 4
b. 2, 4 / 3, 8
c. 5, 6, 2 / 4, 8
d. 5, 6, 1 / 1, 8
Answer: C.
Either Marker 2 or markers 5 and 6 shows-up in each individual of the third generation, who
are decedents of parents 1 & 2 of first generation. Also, either marker 4 or 8 appears in each
individual of the third generation, inherited from parents 3 & 4 of first generation. Hence,
alleles inherited through II-1 should be 5, 6, 2 and that through II-2 should be 4, 8.