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● Microsatellites − These are repetitive DNA sequences.

Observations from HGP

● Human genome contains 3 × 10​(3164.7 million) nucleotide bases.

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● An average gene consists of 3000 bases. However, the size of genes
varies. Largest gene is dystrophin (2.4 m bases).
● Total number of genes in human genome − 30,000

● Over 50% of the discovered genes have unknown functions.
● Less than 2% of genome is coding.

● Large portion of genome consists of repeating sequences.
● Repetitive sequences have no coding function. They are repeated over

hundred to thousand times. They may have a role in evolution,
chromosome structure, and dynamics.

● Chromosome with most genes − Chromosome 1 (2968)
Chromosome with fewest genes − Chromosomes Y (231)
● SNPs (single nucleotide polymorphism) occur at about 1.4 million

locations in human DNA. They are believed to have significance in
explaining diseases and evolutionary history of human beings.

DNA Fingerprinting

Introduction

● DNA fingerprinting is a method for comparing the DNA sequences of
any two individuals.

● 99.9% of the base sequences in all human beings are identical. It is
the remaining 0.1% that makes every individual unique.

● It is a really difficult and time­consuming task to sequence and

compare all 3 × 10​bases in two individuals. So, instead of
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considering the entire genome, certain specific regions called repetitive
DNA sequences are used for comparative study.

Basis of DNA Fingerprinting

● Repetitive DNA is separated from bulk genomic DNA since it appears

as a distinct peak during density gradient centrifugation.
● Major peak: Formed by bulk DNA