The total number of genes in humans is far less (<25000) than the previous estimate (up to 140000 gene). Comment.
The total number of genes is estimated at 25000 much lower than previous estimates of 140000 that had been based on extrapolations from gene-rich areas as opposed to a composite of gene-rich and gene-poor areas.
Almost all (99.9%) nucleotide bases are exactly the same in all people. Functions for over $50 \%$ discovered genes are not known yet. Scientist have identified about 1.4 million locations where single-base DNA difference (SNPs or Single Nucleotide Polymorphisms) occur in humans.
This information promises to revolutionise the processes of finding chromosomal locations for disease-associated sequence and tracing human history.
Now, sequencing of total genomes is getting less expensive day by day. Soon it may be affordable for a common man to get his genome sequenced. What in your opinion could be the advantage and disadvantage of this development?
Human genome helps to find out the complete genome sequence of the human. It has many advantages and disadvantages.
Some important advantages
It provides the knowledge of the effects of variations of DNA among individuals can revolutionise the ways to diagnose, treat and prevent many diseases that affect humans. It also provides clues to the understanding of human biology. It helps to find out the human evolution. Identification through DNA forensics is also possible.
Some important disadvantages
People might discover and untreatable genetic disease. People may abuse the knowledge obtained from the HGP. Problem can occur for the ownership of the genetic test result and the patenting of human genes and DNA. People believe that they are special and unique in their own ways and may wish to remain like that.
Would it be appropriate to use DNA probes such as VNTR in DNA fingerprinting of a bacteriophage?
Bacteriophage does not have repetitive sequences such as VNTRs in its genome, as its genome is very small and have all the coding sequence. DNA finger printing is not done for phages.
During in vitro synthesis of DNA, a researcher used 2', 3'-dideoxy cytidine triphosphate as raw nucleotide in place of $2^{\prime}$-deoxy cytidine. What would be the consequence?
Further polymerisation would not occur, as the $3^{\prime} \mathrm{OH}$ on sugar is not there to add a new nucleotide for forming ester bond.
That background information did Watson and Crick have made available for developing a model of DNA? What was their contribution?
Watson and Crick had the following informations which helped them to develop a model of DNA.
(i) Chargaff's Law suggesting $\mathrm{A}=\mathrm{T}$ and $\mathrm{C}=\mathrm{G}$
(ii) Wilkins and Rosalind Franklin's work on DNA crystal's X-ray diffraction studies about DNAs physical structure.
Watson and Crick proposed
(a) Pattern of complementary bases pair
(b) Semi-conservative replication
(c) Mutation through tautomerism