Mention salient features of human genome.
 

Salient Features of Human Genome

Some of the salient observations drawn from human genome project are as follows:
$(i)$ The human genome contains $3164.7$ million nucleotide bases.
$(ii)$ The average gene consists of $3000$ bases, but sizes vary greatly, with the largest known human gene being dystrophin at $2.4$ million bases.
$(iii)$ The total number of genes is estimated at $30,000-$ much lower than previous estimates of $80,000$ to $1,40,000$ genes. Almost all ( $99.9$ per cent) nucleotide bases are exactly the same in all people.
$(iv)$ The functions are unknown for over $50$ per cent of discovered genes.
$(v)$ Less than $2$ per cent of the genome codes for proteins.
$(vi)$ Repeated sequences make up very large portion of the human genome.
$(vii)$ Repetitive sequences are stretches of $DNA$ sequences that are repeated many times, sometimes hundred to thousand times. They are thought to have no direct coding functions, but they shed light on chromosome structure, dynamics and evolution.
$(viii)$ Chromosome $1$ has most genes $(2968)$, and the $Y$ has the fewest $(231)$.
$(ix)$ Scientists have identified about $1.4$ million locations where singlebase $DNA$ differences ($SNPs-$ single nucleotide polymorphism, pronounced as ‘snips’) occur in humans. This information promises to revolutionise the processes of finding chromosomal locations for disease associated sequences and tracing human history.