Ch 6. Molecular Basis of Inheritance (Stack 4)

Question 1

Mention the four levels at which regulation of gene expression can be exerted in eukaryotes

Answer 1

1. transcriptional level (formation of primary transcript)
2. processing level (regulation of splicing)
3. transport of mRNA from nucleus to the cytoplasm
4. translational level.

Question 2

Mention the role of repressor and inducer in regulation of gene expression

Answer 2

• The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon.
• In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and transcription proceeds.

Question 3

How does the Lac-operon function in the absence of inducer (lactose) in the medium?

Answer 3

The repressor of the operon is synthesised (all-the-time - constitutively) from the i gene. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon.

Question 4

What are expressed sequence tags?

Answer 4

1. All the genes that are expressed as RNA

Question 5

Define sequence annotation

Answer 5

Assigning the different regions in the DNA sequence with functions is termed as sequence annotation.

Question 6

Mention a common vector used for the amplification of DNA fragments during the sequencing of human genome

Answer 6

Bacterial artificial chromosome (BAC) and Yeast artificial chromosome

Question 7

Which is the largest known human gene?

Answer 7

Dystrophingene

Question 8

Which chromosome in humans has the largest number of genes?

Answer 8

Chromosome 1

Question 9

Which chromosome in humans has the least number of genes?

Answer 9

Chromosome Y

Question 10

With reference to Human Genome Project, what do SNPs refer to?

Answer 10

Single nucleotide polymorphism

Question 11

What is single nucleotide polymorphism

Answer 11

The locations where single base DNA differences are seen in human genome

Question 12

Mention any two goals of Human Genome Project

Answer 12

1. Identify all the approximately 20,000-25,000 genes in human DNA
2. Determine the sequences of the 3 billion chemical base pairs that make up human DNA

Question 13

Mention the two approaches with respect to the methodology of sequencing DNA in Human Genome Project.

Answer 13

• One approach focused on identifying all the genes that are expressed as RNA (referred to as Expressed Sequence Tags (ESTs).
• The other took the blind approach of simply sequencing the whole set of genome that contained all the coding and non-coding sequence, and later assigning different regions in the sequence with functions (a term referred to as Sequence Annotation).

Question 15

Mention two salient features of human genome

Answer 15

1. The human genome contains 3164.7 million nucleotide bases.
2. The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases.

Question 16

What is repetitive DNA?

Answer 16

Small stretch of DNA sequences which are repeated many times

Question 17

What is satellite DNA

Answer 17

The type of repetitive DNA which appears as small peaks after density gradient centrifugation is called satellite DNA

Question 18

Define DNA polymorphism

Answer 18

The inheritable mutations observed in a population at high frequency is called DNA polymorphism

Question 19

Expand VNTR.

Answer 19

Variable number of tandem repeats

Question 20

What is a VNTR probe or DNA probe?

Answer 20

A short segment of artificially synthesised, radio labelled DNA complementary to the VNTR regions.

Question 21

’ Restriction endonucleases are important tools in DNA finger printing technique’. Justify

Answer 21

RENs helps in fragmentation of DNA during DNA fingerprinting

Question 22

Why gel electrophoresis is an important step in DNA fingerprinting

Answer 22

1. Because , it helps in separation of fragments of different size

Question 23

Mention one application of DNA fingerprinting

Answer 23

Solving paternity disputes

Question 24

List out three applications of DNA fingerprinting

Answer 24

• Solving paternity disputes
• Solving crime cases by identifying the culprit
• Determining population and genetic diversities.

Question 25

List the steps of DNA finger printing technique

Answer 25

1. isolation of DNA,
2. digestion of DNA by restriction endonucleases,
3. separation of DNA fragments by electrophoresis,
4. transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon,
5. hybridisation using labelled VNTR probe, and
6. detection of hybridised DNA fragments by autoradiography.