AIIMS AIPMT MCAT JIPMER Molecular Basis of Genetics MCQs

1. ABO blood groups in humans are controlled by the gene /. It has three alleles – /*, /’ and /. Since there are three different alleles, six different genotypes are possible. How many phenotypes can occur?
(a) Three (b) One (c) Four (d) Two.
2. Which of the following disorders are caused due to recessive autosomal mutations?
(a) Turner’s syndrome and sickle cell anaemia
(b) Edward’s syndrome and Down’s syndrome
(c) Cystic fibrosis and phenylketonuria
(d) Alzheimer’s disease and Huntington’s chorea.
3. A test cross is carried out to
(a) determine the genotype of a dominant phenotype
(b) predict whether two traits are linked
(c) assess the number of alleles of a gene
(d) determine whether two species or varieties will breed successfully.
4. Some of the dominant traits studied by Mendel were
(a) round seed shape, constricted pod shape and axial flower position
(b) green pod colour, inflated pod shape and axial flower position
(c) yellow seed colour, violet flower colour and yellow pod colour
(d) axial flower position, green pod colour and green seed colour.
5. Which one of the following conditions correctly describes the manner of determining the sex?
(a) Homozygous sex chromosomes (ZZ) determine female sex in birds.
(b) XO type of sex chromosomes determine male sex in grasshopper.
(c) XO condition in humans as found in Turner’s syndrome, determines female sex.
(d) Homozygous sex chromosomes (XX) produce male in Drosophila.
6. Which one of the following is not a part of a transcription unit in DNA?
(a) The inducer (b) A terminator
(c) A promoter (d) The structural gene.
7. Albinism is known to be due to an autosomal recessive mutation. The first child of a couple with normal skin pigmentation was an albino. What is the probability that their second child will also be an albino?
(a) 50% (b) 75% (c) 100% (d) 25%.
8. The number of codons that code amino acids is
(a) 16 (b) 31 (c) 61 (d) 64.
9. The lac operon is turned on when allolactose molecules bind to
(a) promoter site (b) operator site
(c) mRNA (d) repressor protein.
10. Which of the following situation will be fatal to first foetus?
(a) if Rh+ man marries Rh+ woman
(b) if Rh- man marries Rh+ woman
(c) if Rh+ man marries Rh- woman
(d) if Rh- man marries Rh- woman.
11. What would be the percentage of thymine in a double stranded DNA sample which contains 20% cytosine of the total bases?
(a) 10% (b) 20% (c) 30% (d) 40%.
12. Select the correct statement regarding protein synthesis.
(a) When the small subunit of the ribosome encounters an mRNA the process of translation begins.
(b) Peptidase catalyzes the formation of peptide bond.
(c) UTRs are present between the start codon and stop codon.
(d) At the end of translation the release factor binds to the initiation codon.
13. Which among the following codons does not have /RNAs?
(a) Start codon (b) AUG
(c) GGG (d) Stop codon.
14. To which of the following factors, RNA polymerase binds transiently to initiate transcription?
(a) Rho (b) Beta (c) Gamma (d) Sigma.
15. Barr bodies are seen in
(a) somatic cells of normal human female
(b) germ cells of normal human female
(c) somatic cells of normal human male
(d) somatic cells of supermale.
16. The end of fragments of DNA molecule are sticky due to
(a) free methylation (b) endonuclease
(c) unpaired bases (d) calcium ions.
17. Histone octamer contains
(a) eight types of histones
(b) eight histones of four different types
(c) five histones
(d) six types of histones.
18. Methyl guanosine triphosphate is associated with
(a) point mutation (b) tautomerism
(c) capping (d) Okazaki fragments.
19. Match the enzyme in column I with its function in column II and select the correct option.

120. Locations or sites in the human DNA where single base DNA differences occurs are called
(a) repetitive DNA (b) VNTR
(c) SNP (d) SSCP.

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