The Complete Human Genome

Subject: Science & Tech

Section: Biotechnology

Context- Two decades after most of the human genome was mapped, scientists have now filled in the gaps that remained.

Concept-

Nearly two decades ago, when scientists published the map of the human genome for the first time, it was hailed as a breakthrough.
That was incomplete, however: about 8% of the human DNA was left unsequenced.
Now, in a series of papers published in Science, a large team has accounted for that 8%, completing the picture of the human genome for the first time.

What was missing:

The genetic sequence made available in 2003 from the Human Genome Project, an international collaboration between 1990 and 2003, contained information from a region of the human genome known as the euchromatin. Here, the chromosome is rich in genes, and the DNA encodes for protein.
The 8% that was left out was in the area called heterochromatin. This is a smaller portion of the genome, and does not produce protein.
Now, the fully sequenced genome is the result of the efforts of a global collaboration called the Telomere-2-Telomere (T2T) project.
What’s in the 8%

What does genome-mapping tell us?

According to the Human Genome Project, there are estimated to be over 20,500 human genes.
- Genome refers to an organism’s complete set of DNA, which includes all its genes and mapping these genes simply means finding out the location of these genes in a chromosome.
In humans, each cell consists of 23 pairs of chromosomes for a total of 46 chromosomes, which means that for 23 pairs of chromosomes in each cell, there are roughly 20,500 genes located on them.
Some of the genes are lined up in a row on each chromosome, while others are lined up quite close to one another and this arrangement might affect the way they are inherited.
For example, if the genes are placed sufficiently close together, there is a probability that they get inherited as a pair.
Genome mapping, therefore, essentially means figuring out the location of a specific gene on a particular region of the chromosome and also determining the location of and relative distances between other genes on that chromosome.

Significance of Genome Mapping:

A complete human genome makes it easier to study genetic variation between individuals or between populations.
Genome mapping enables scientists to gather evidence if a disease transmitted from the parent to the child is linked to one or more genes.
Mapping also helps in determining the particular chromosome which contains that gene and the location of that gene in the chromosome.
According to the National Human Genome Research Institute (NHGRI), genome maps have been used to find out genes that are responsible for relatively rare, single-gene inherited disorders such as cystic fibrosis and Duchenne muscular dystrophy.
Genetic maps may also point out scientists to the genes that play a role in more common disorders and diseases such as asthma, cancer and heart disease among others.

Human Genome Project:

In 1990, with support from the US and widespread international collaboration and cooperation, the $3 billion dollar Human Genome Project was launched.
The project aimed to determine the sequence of the human genome within 15 years.
Human genome project (HGP) got successfully completed in the year 2003 by sequencing the almost entire human genome (except 8%) of 3.3 billion base pairs.