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Saturday, 24 July 2021

MCQs ll Molecular Basis of Inheritance - 2 ll Genetics ll NEET

MCQs ll Molecular Basis of Inheritance - 2 ll Genetics ll NEET 

 

Watch lectures on my you tube channel:  https://bit.ly/3Bzgc2k  

 

1. The point, at which polytene chromosome appear to be attached together, is called

(a) centromere

(b) chromomere

(c) chromocentre

(d) centriole.

Answer and Explanation: YouTube Lectures

1. (c): Chromocentre is junction point of the chromosomes in the polytene salivary glands of Drosophila larvae. Unlike the situation in other cells, the giant chromosomes of these cells persist through interphase, the two homologous copies of each chromosome are attached together throughout their lengths and all the chromosomes are joined together by a chromocentre.

2. In split genes, the coding sequences are called

(a) exons

(b) cistrons

(c) introns

(d) operons.

Answer and Explanation: YouTube Lectures

2. (a): Split gene are those genes that consist of continuous sequence of nucleotide (coding sequence) interrupted by intervening sequences. Most eukaryotic genes are split as are genes of some animal viruses. The continous coding sequences are called exons and the intervening non-coding sequences are called introns. These introns are not represented in mRNA transcribed from the gene and are not utilized for the synthesis of proteins.

3. The polytene chromosomes were discovered for the first time in

(a) Drosophila

(b) Musca domestica

(c) Chironomus

(d) Musca nebula.

Answer and Explanation:

3. (c): In salivary glands cells of Chironomus tantans giant chromosomes were observed by E.GBalbini for the first time in 1881. The availability of these chromosomes greatly helped in the study of Drosophila cytogenetics in which they were discovered later.

4. Each chromosome at the anaphase stage of a bone marrow cell in our body has

(a) two chromatids

(b) several chromatids

(c) no chromatids

(d) only one chromatid.

Answer and Explanation: YouTube Lectures

4. (d): A bone marrow cell is a somatic cell and therefore mitosis takes place in it. During mitosis anaphase chromosomes split at centromere. Sister chromatids seperate from each other, so that the two sister chromatids are separate structures and can now be called as chromosomes.

5. If the DNA codons are ATG ATG ATG and a cytosine base is inserted at the beginning, then which of the following will result?

(a) CAT GAT GATG

(b) a non-sense mutation

(c) C ATG ATG ATG

(d) CATGATGATG

Answer and Explanation: YouTube Lectures

5. (a): Nonsense mutation is a mutation which interconverts a nonsense to or from a sense-coding triplet, resulting in an abnormally foreshortened or elongated polypeptide chain. But in this example cytosine is added at the beginning so CAT GAT GATG. will result.

6. Barr body in mammals represents

(a) all the heterochromatin in male and female ceils

(b) the Y-chromosome in somatic cells of male

(c) all the heterochromatin in female cells

(d) one of the two X-chromosomes in somatic cells of females.

Answer and Explanation:

6. (d): Barr body is a condensed heterochromatic copy of the X chromosome, visible by staining the interphase nucleus of somatic cells of the homogametic sex, for example the human female. Named after M. Barr, these condensed chromosomes offer an easy way of determining the true genetic sex of individuals with intermediate secondary sexual characteristics. The total number of Barr bodies is always one less than the total number of X chromosomes present in the cell or the organism.

7. If the sequence of bases in DNA is ATTCGATG, then the sequence of bases in its transcript will be

(a) GUAGCUUA

(b) AUUCGAUG

(c) CAUCGAAU

(d) UAAGCUAC.

Answer:

(d) UAAGCUAC.

8. An environmental agent, which triggers transcription from an operon, is a

(a) depressor

(b) controlling element

(c) regulator

(d) inducer.

Answer:

(d) inducer

9. The lac operon is an example of YouTube Lectures

(a) repressible operon

(b) overlapping genes

(c) arabinose operon

(d) inducible operon.

Answer and Explanation:

9. (d): Lac operon (lactose operon). Genetic system of E.coli is responsible for the uptake and initial catabolism of lactose. The lac operon consists of three structural genes (lac Z, lac Y, lac A), lac Z codes for p- galactosidase which hydrolyses lactose to glucose and galactose. (lacY codes for lac permease, a membrane- bound protein constituent of the lactose transport system, lac A codes of thioglactoside transacetylase, an enzyme of uncertain metabolic function.

Bacteria growing in a lactose-free medium contain about five molecules of P-glactosidase per cell. The appearance of P-galactosidase is coordinated with the production of permease and transacetylase. On removing lactose from the medium enzyme synthesis stops.

Such enzymes whose synthesis can be induced by adding the substrate are known as inducible enzymes and the genetic systems responsible for the synthesis of such an enzyme are known as inducible operons.

10. The wild type E.coli cells are growing in normal medium with glucose. They are transferred to a medium containing only lactose as sugar. Which of the following changes take place?

(a) the lac operon is induced

(b) E.coli cells stop dividing

(c) the lac operon is repressed

(d) all operons are induced.

Answer and Explanation: YouTube Lectures

10. (a): When E.coli bacteria are transfered to medium containing lactose, then the lac opeon is indueed. The lac opeaon consists of 3 structural gene (lac Z, lac Y and lac A). It involves the synthesis of P-galactosidase enzyme in E.coli, which hydrolyses lactose into glucose and galactose.

 

Watch lectures on my you tube channel: https://bit.ly/3Bzgc2k 

 

11. Radio-tracer technique shows that DNA is in

(a) multi-helix stage

(b) single-helix stage

(c) double-helix stage

(d) none of these.

Answer and Explanation:

11. (c): Autoradiography is the study of labelled precursors like 3H by knowing the movement of radioactivity with the help of photographic films and emulsions at short intervals. 14C and 3H are incorporated in bases like thymidine, uridine and amino acids to study the structure of DNA and proteins. Radio tracer technique shows that DNA is in double helical form.

12. The codons causing chain termination are

(a) AGT, TAG, UGA

(b) UAG, UGA, UAA

(c) TAG TAA, TGA

(d) GAT, AAT, AGT.

Answer and Explanation:

12. (b): Nonsense codon also called stop codon, or termination codon are any of the three codons that do not code for an amino acid, but instead cause termination of protein synthesis. They are recognised by proteins called release factors which bind to the A site of the iebosome They are UGA, UAG, UAA, of which UAG is known as amber, UAA as ochre, and UGA as opal.


13. Which of the following serves as a terminal codon?

(a) UAG

(b) AGA

(c) AUG

(d) GCG.

Answer and Explanation: YouTube Lectures

13. (a): In eukaryotes, the termination of polypeptide chain during translation is brought about by the terminating codons. These are UAA, UAG and UGA and these are called as amber, ochre and opal respectively. These codons are also called as nonsense codons as they donot code for any amino acid. In phages and bacteria there may be many initiating and terminating codons and thus as many polypeptides are synthesized. AUG is the initiation codon. It codes for methionine amino acid.

14. Identify the one, which causes mutation

(a) cosmic rays

(b) hromosomes

(c) crossing over

(d) X-rays.

Answer and Explanation:

14. (d): Mutations can be artificially induced with the help of mutagenic agents which can be broadly classified into two groups, physical mutagens and chemical mutagens. Physical mutagens are mainly radiations, although change in pH value (acidity) or temperature shocks may also induce mutations.

Among ionizing radiations, more commonly X-rays, gamma rays, beta rays and neutrons are used for inducing mutations. X-rays are produced in a X-ray machine when energy charged particles like cathode rays (electrons) impinge on a suitable target like tungston.

15. Lampbrush Chromosomes are seen in which typical stage?

(a) mitotic metaphase

(b) meiotic prophase

(c) mitotic anaphase

(d) mitotic prophase.

Answer and Explanation:

15. (b): Lampbrush chromosomes (Ruckert, 1892) are large sized diplotene chromosome bivalents with a length of 400 – 1000 nm each and a total length of 5900 in Triturus (Salamander = Newt). A lampbrush chromosome is made of two homologous chromosomes held at several places by chiasmata. Each chromosome has an axis with alternate chromosomes held at several places by chiasmata.

Each chromosome has an axis with alternate chromomeres and interchromomeric areas. Many of the chromomeres give out lateral loops of various sizes which are thin in the region of origin and thick in the area where they are wound back into chromomeres. Loops possess a number of copies of the same gene and are meant for rapid transcription and production of materials like yolk. Hence, lampbrush chromosomes occur in oocytes.

16. Which of the following step of translation does not consume a high energy phosphate bond?

(a) peptidyl transferase reaction

(b) aminoacyl /-RNA binding to ,4-site

(c) translocation

(d) amino acid activation.

Answer and Explanation:

16. (a): Protein synthesis or translation consists of ribosomes, amino acids, mRNA, tRNAs and aminoacyl tRNA synthetases. The ribosomes have two binding sites namely aminoacyl site or A-site and peptide site or P- site. The starting amino acid methionine lies at the P- site of the ribosome.

The next incoming tRNA is called amino acyl tRNA, it is bound to A-site. A peptide bond is formed between COOH group of the t-RNA at P-site and NH2 group of aminoacyl t-RNA. This is facilitated by the enzyme peptidyl transferase and does not require high energy phosphate bonds.

17. The RNA that picks up specific amino acid from amino acid pool in the cytoplasm to ribosome during protein synthesis is called

(a) r-RNA

(b) RNA

(c) m-RNA

(d) t-RNA.

Answer and Explanation:

17. (d): Transfer RNA or tRNA help in transfer of amino acids to ribosomes mRNA complex to form the polypeptide chain. It has four key regions a carrier and recognition end, enzyme site and ribosome site. This recognition end has three anticodons with the help of which aminoacids are identified. r-RNA forms 67% of 70s ribosomes and 50% of 80s ribosomes.

mRNA carries the coded information from DNA for the synthesis of proteins.

18. DNA synthesis can be specifically measured by estimating the incorporation of radio-labelled

(a) thymidine

(b) deoxyribose sugar

(c) uracil

(d) adenine.

Answer and Explanation:

18. (a): Autoradiography is the study of labelled precursors like 3H by knowing the movement of radioactivity with the help of photographic films and emulsions at short intervals.

Radioactive material like tritiated thymidine which is formed by replacing normal hydrogen of thymidine with H3 (heavy isotope of hydrogen). Thymidine only is used for this purpose because RNA will not be labelled by this.

49. Genetic identity of a human male is determined by

(a) sex-chromosome

(b) cell organelles

(c) autosome

(d) nucleolus.

Answer and Explanation: YouTube Lectures

19. (a): Sex chromosomes are those chromosomes whose presence, absence or particular form determines the sex of the individual in unisexual or dioecious organisms, e.g., XX – XY. XY method (XX – XY). It occurs in mammals and many insects with females having homomorphic XX sex chromosomes and males possessing heteromorphic XY – chromosomes. In human being the Y-chromosome is straight and acrocentric (centromere subterminal near one end).

It is about 2 µm in length and is thus the shortest of all chromosomes. X- chromosome is 5.0 – 5.5 µm in length. It is metacentric (centromere in the middle). Despite differences in morphology, XY chromosomes synapse during zygotene. They have two parts, homologous and differential. Homologous regions of the two take part in synapsis.

20. Genes located at the same locus of chromosomes are called

(a) multiple alleles

(b) polygenes

(c) oncogenes

(d) none of these.

Answer and Explanation:

20. (a): Genes located on the same locus of chromosomes are called multiple alleles. They are produced due to repeated mutations of the same gene but in different directions. Multiple alleles being located on the same locus do not show crossing over.

 

Watch lectures on my you tube channel: https://bit.ly/3Bzgc2k 

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