Date: 06/10/2022

Relevance: GS-3: Science and Technology- developments and their applications and effects in everyday life.

Key Phrases: Human Evolution, Stages of Evolution of Human, Genome and Genome Sequencing, Neanderthals, hominins, Noble prize in Physiology

Context:

• The 2022 Nobel Prize for Physiology has been awarded to Swedish geneticist Svante Pääbo for his research in the field of genomes of extinct hominins and human evolution.

Background

• The prize was announced by the Royal Swedish Academy of Sciences in Stockholm.
• Dr Svante Pääbo’s discoveries show that archaic gene sequences from our extinct relatives influence the physiology of present-day humans.
  • For example the Denisovan version of the gene EPAS1, which confers an advantage for survival at high altitudes and is common among Tibetans.
  • Other examples are Neanderthal genes that affect our immune response to different types of infections

All about Svante Pääbo’s research

• Dr. Pääbo’s groundbreaking research attempts to answer questions about human evolution.
• He sequenced the genome of Neanderthal, a species of humans that existed on the earth and went extinct around 30,000 years ago.
• He also discovered Denisova – a previously-unknown hominin. (Hominins are extinct members of the human lineage.)
• Dr. Pääbo’s research led him to the conclusion that “gene transfer had occurred from these now extinct hominins to Homo sapiens following the migration out of Africa around 70,000 years ago”.
• This ancient gene flow has significant physiological relevance for present-day humans.

What is Genome?

• A genome is all the genetic matter in an organism.
• It is defined as an organism’s complete set of Deoxyribose Nucleic Acid (DNA), including all of its genes.
• In humans, a copy of the entire genome contains more than 3 billion DNA base pairs.
• Chromosomes
  • In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes.
  • Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
  • In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46.
  • Twenty-two of these pairs, called autosomes, look the same in both males and females.
  • The 23rd pair, the sex chromosomes, differ between males and females. Females have two copies of the X chromosome, while males have one X and one Y chromosome.

Challenges and problems

• The idea of studying the DNA of Neanderthals was not an easy task because DNA tends to degrade and become chemically modified.
• It is highly fragmented and may lead to full contamination from microbes like fungi and bacteria
• Since Neanderthals became extinct 30,000 years ago, only trace amounts of their DNA would have been left in fossils
• Amplifying and Sequencing of DNA is not easy especially in places like India and Africa because the ancient DNA is not preserved well in tropical weather conditions.

Distinguishing the Neanderthals

• Dr. Pääbo first studied mitochondrial DNA from Neanderthals because Mitochondria have their own DNA.
• Although the mitochondrial genome is small and only contains a fraction of genetic information in the cell, it is present in thousands of copies.
  • This increases the chance of its successful genome sequencing.
• Dr. Pääbo was successful in sequencing a part of mitochondrial DNA from a 40,000-year-old bone.
• A comparison of this with contemporary humans and chimpanzees showed that Neanderthals were genetically distinct.

Establishing distinctions with the present human species

• DNA sequences from Neanderthals were also found to be more similar to sequences from contemporary humans originating from Europe or Asia than to contemporary humans originating from Africa.
  • It suggested interbreeding between Neanderthals and Homo sapiens during their coexistence.
• Dr. Pääboon’s 2010 draft sequence of the Neanderthal genome outlined his team’s analysis of 21 Neanderthal bones from Vindija Caves in Croatia.
• Bone powder from these specimens was analyzed and three bones were selected for further analysis.
• Nine DNA extracts were prepared from the three bones factoring the DNA and microbial contamination before continuing with the investigation.
• Five present-day human genomes from different regions – South Africa, West Africa, Papua New Guinea, China and France were sequenced and analyzed against the Neanderthal genome derived from the experiment.
  • It was noted that the divergence of the Neanderthal genome to the human reference genome was greater than for any of the present-day human genomes that had been analyzed.

Finding the Denisova

• In 2008, Dr. Pääbo’s team sequenced the DNA from an “exceptionally well-preserved", 40,000-year-old fragment from a finger bone found in the Denisova cave in Siberia.
• This DNA sequence turned out to be unique – different from all-known sequences from Neanderthals and present-day humans.
• Comparisons with DNA sequences of contemporary humans from different parts of the world carried out
• This also suggested gene flow between them and the unknown hominin Denisova.

Significance

• Dr. Pääbo’s research established a new scientific disciple called paleogenomics (study and analysis of genes of ancient or extinct organisms)
• Dr Paabo’s conceptual breakthrough is of paramount importance in understanding human evolution.
• At the same time, his technological breakthrough is notable because it is not easy to amplify and sequence ancient DNA.
• This research has helped in furthering the recognition of evolutionary biology and paleogenomics.

Conclusion

• The current research by Dr. Pääbo is a great leap forward which may open many doors in the field of genetics and human evolution.
• It remains to be seen if the renewed interest in the field will lead to better funding and subsequently more opportunities for researchers.

Source: The Hindu

Mains Question:

Q. “Archaic gene sequences from extinct relatives influence the physiology of present-day humans.” In view of the statement, explain the concept of Genome and genome sequencing. How is it significant for the human race? (250 words).