IIT JAM Biotechnology Mock Test 3 - IIT JAM MCQ

Prokaryotic chromosome is made up of supercoiled DNA wrapped with non-histone proteins called nucleoid. In eukaryotes, DNA is wrapped around basic histone proteins to form chromatin fibres.

Ribososmes are ribonucleoproteins, which consist of 2 components: RNA and proteins. In prokaryotes, ribosomes consist of 23S rRNA, 16S rRNA, 5S rRNA and ribosomal proteins. While in eukaryotes they consist of the 18S rRNA, 28S rRNA, 5S rRNA and 5.8S rRNA and ribosomal proteins.

Telomerase, also called terminal transferase, is a ribonucleoprotein that adds species-dependent telomeric repeat sequences to the 3' end of chromosomes to prevent telomere shortening. A telomere is a region of repetitive sequences at each end of eukaryotic chromosomes in most eukaryotes.

Protein coding genes in prokaryotes are polycistronic (multiple genes under a common promoter), have a single replication origin and a single transcription start at promoter region. Thus, none of the given options are true.

The genes that are carried on the Y chromosome are called holandric genes. Holandric genes can only be passed by males onto their sons; they code for ‘maleness’ but sometimes cause rare conditions like hypertrichosis pinnae and color blindness.

Three or more alternative forms of a gene (alleles) that can occupy the same locus is the condition of multiple alleles. However, only two of the alleles can be present in a single organism. For example, the ABO system of blood groups is controlled by three alleles (i^A, i^B, i^O).

Linkage group, in genetics, refers to all of the genes on a single chromosome. They are inherited as a group; that is, during cell division they act and move as a unit rather than independently. In human beings, each of the 23 pairs of homologous chromosome represent one linkage group.

Monosomy is the condition of having a diploid chromosome complement in which one chromosome lacks its homologous partner that is 2n-1. Turner syndrome is the best example with genome 45, X0.

Trophoblast is the layer of cells encircling the blastocoel and the inner cell mass. The latter gives rise to the embryo. The cells of the trophoblast form the placenta and foetal membrane

Ectoderm, mesoderm and endoderm are the three germ layers that give rise to specific tissues, organs and organ systems. Gonads, muscles, dermis, kidneys etc. develop from mesoderm. Ectoderm produces epidermis, glands, nervous system etc. Pancreas, lining of urinary bladder etc develop from endoderm.

In bacteria, DNA polymerase III is the main replicating polymerase which synthesises leading as well as lagging strand. After the synthesis is complete, primers from the okazaki fragments (in lagging strand) are removed by DNA polymerase I, which consists of 3’-5’exouclease activity.

5’ UTR (5’ untranslated region) is the region of mRNA immediately upstream of the initiation codon or translation start site. This region is transcribed into mRNA transcript but does not code any amino acid in the corresponding protein.

Sno-RNA (small nucleolar RNA) has a role in processing and chemical modification of ribosomal RNAs.  5’ capping of RNA with 7-methyl guanosine helps in ribosome recognition of mRNA to initiate translation.DNA polymerase binds at OriC to initiate DNA replication. Transcription attenuation is a regulatory mechanism associated with tryptophan operon, whereby transcription of structural genes of tryptophan operon are controlled.

All the statements mentioned in the question are correct except statement c. Chargaff’s laws do not apply to ssDNA and RNA and hence for ssDNA, the amount of A is not necessarily equal to T; amount of G is not necessarily always equal to C. But for dsDNA the amount of A is always equal to T; amount of G is always equal to C. Therefore in an organism (A+T)/(C+G)=variable, but (A+G)/(C+T)=1.0.

All the characteristics mentioned in the question i.e. semi conservative replication, inducible operons, leading and lagging stands apply to prokaryotic cells except poly-A tail. Poly-A tail, is a post-transcriptional modification exclusive to eukaryotic mRNA

When the cations are added to DNA solution, the melting temperature (Tm) of DNA increase. The reason for this is that cations have positive charge, which bind to the negative phosphate backbone of DNA, thereby shielding the negative charge, due to which DNA double helix is stabilized and its Tm increases.

Bacterial lac operon consists of three structural genes involved in transport and utilization of lactose, under the control of a common promoter.In the schematic of lac operon given in the statement; P is the promoter, lacI-repressor, O is operator which is the binding site of repressor protein, product of lac I gene.Z, Y and A form the structural genes that encode beta galactosidase, permease and transacetylase enzymes respectively.

Tryptophan operon consists of 5 structural genes involved in the tryptophan synthesis, under the control of single promoter. It can be regulated by two mechanisms: (a) Tryptophan repressor ;(b) Attenuation. In addition to, regulation by the trp repressor, attenuation is also a mechanism for reducing expression of the trp operon when levels of tryptophan are high. However, rather than blocking initiation of transcription, attenuation prevents completion of transcription.

9:3 :4 ratio depicts that it is the case of recessive epistasis interaction.

Gene Ac an modify the yellow precursor into brown.
Gene B can modify the brown colour into black.

Tliat means gene A is in homozygous recessive epistatic state over gene B.

In recessive epistasis the recessive alleles at one locus (aa) mask the phenotypic expression of other gene locus (BB, Bb or bb) such epistasis is called recessive epistasis. The alleles of ‘B’ locus express themselves only when epistatic locus ‘A’ has dominant allele like AA or Aa. The phenotypic ratio is 9: 3: 4 (instead of 9:3:3:1).

AAbb (white or colourless flower) x aaBB (white or colourless flower)
→ So. it is the case of complimentary gene interaction in which two genes A and B control the pigment colour of the flowers of sweet pea.
So. when mutation is present in one of alleles of both genes then complementation occurs and purple pigmentation is produced.

Non-disjunction at second division produces both normal and aneuploid gametes.

In a three point test cross, the most abundant progenies represent the parental genotypes, while the rarest progenies are the product of the double cross over between the genes. So comparing the two genotypes the gene order can be explained as  A-C-B.

Genes that are close to point of the origin (O) transfer first to the recipient cells, so highest frequency in the populations.

The Hardy–Weinberg equation for three alleles, p, q and r respectively is represented by  P+ Q+ R = 1. Then the frequencies of the genotypes are given by
(P + Q + R)² = P² + Q² + R² + 2PQ + 2PR + 2PQ = 1

Triticale is  aman made improved variety of wheat.  An allopolyploid, obtain from the cross between tetraploid wheat and a diploid rye plant that obtained a hexaploid wheat triticale.

Dorsal most vegetal endodermal cells  consist of Nieuwkoop’s centre which induce the dorsal most mesodermal cells to form dorsal lip of blastopore

PTTH is secreted by neuro-secretory cells of brain and stores into Corpora cadiacum, which releases it at some appropriate time.

Grey crescent is the area just opposite to the site of entry of sperm into ovum. It marks the future dorsal side of the embryo.

Embro sac which consist of 7 haploid cells and 8 nuclei represents the female gametophyte generation in angiosperm plant.