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Why is Neanderthal Genetic material Found in only Small amount in Genomes of Modern Humans?

The scientists estimated that these gene variations were able to persist in Neanderthals because Neanderthals had a much smaller population size than humans

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FILE - A model of an adult Neanderthal male head and shoulders by artist John Gurche on display in the Hall of Human Origins in the Smithsonian Museum of Natural History in Washington, D.C. VOA

New York, November 9, 2016: Neanderthal genetic material is found in only small amount in the genomes of modern humans because, after inter-breeding, natural selection removed large numbers of weakly deleterious Neanderthal gene variants, says a study.

Humans and Neanderthals inter-bred tens of thousands of years ago, but today, Neanderthal DNA makes up only one to four per cent of the genomes of modern non-African people.

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“For a while now we have known that humans and Neanderthals hybridised. Many Europeans and Asians – along with other non-African populations – are the descendants of those hybrids,” said Ivan Juric from the University of California, Davis in the US.

“Previous work has also shown that, following hybridisation, many Neanderthal gene variants were lost from the modern human population due to selection. We wanted to better understand the causes of this loss,” Juric noted.

To understand how modern humans lost their Neanderthal genetic material and how humans and Neanderthals remained distinct, the researchers developed a novel method for estimating the average strength of natural selection against Neanderthal genetic material.

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They found that natural selection removed many Neanderthal alleles from the genome that might have had mildly negative effects.

The scientists estimated that these gene variations were able to persist in Neanderthals because Neanderthals had a much smaller population size than humans.

Once transferred into the human genome, however, these alleles became subject to natural selection, which was more effective in the larger human populations and has removed these gene variants over time.

“Our results are compatible with a scenario where the Neanderthal genome accumulated many weakly deleterious variants, because selection was not effective in the small Neanderthal populations. Those variants entered the human population after hybridisation,” Juric said.

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“Once in the larger human population, those deleterious variants were slowly purged by natural selection,” Juric noted.

These findings, published in the journal PLOS Genetics, shed new light on the role of population size on losing or maintaining Neanderthal ancestry in humans. (IANS)

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Genetic Variations Influence Risk of Developing Cancer: Study

Study found that variations in the regions that regulate the expression of oncogenes and tumour suppressor genes affect cancer risk

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Cancer
While minor genetic changes only have a small impact on Cancer risk, the variations analysed in this study are numerous and common in the population. Pixabay

Shedding new light on why some people develop cancer while others do not, a new study has found that a person’s risk of developing cancer is affected by Genetic variations in regions of DNA that do not code for proteins, previously dismissed as “junk DNA”.

This study, published in the British Journal of Cancer, shows that inherited cancer risk is not only affected by mutations in key cancer genes, but that variations in the DNA that controls the expression of these genes can also drive the disease.

The researchers believe that understanding how non-coding DNA affects the development of this disease could one day improve genetic screening for cancer risk.

And in the future, this could lead to new prevention strategies, or help doctors diagnose the disease earlier, when it is more likely to be treated successfully.

“What we found surprised us as it had never been reported before — our results show that small genetic variations work collectively to subtly shift the activity of genes that drive cancer,” said lead researcher of the study John Quackenbush, Professor at Harvard T.H. Chan School of Public Health in the US.

Genetic
Shedding new light on why some people develop Cancer while others do not, a new study has found that a person’s risk of developing cancer is affected by genetic variations in regions of DNA that do not code for proteins, previously dismissed as “junk DNA”. Pixabay

“We hope that this approach could one day save lives by helping to identify people at risk of cancer, as well as other complex diseases,” Quackenbush said.

The researchers investigated 846 genetic changes within non-coding stretches of DNA, identified by previous studies as affecting cancer risk.

These Single Nucleotide Polymorphisms (SNPs) are particular positions in the human genome where a single letter of the genetic code varies between people.

Unlike mutations in coding DNA, such as BRCA, that are rare but significantly raise a person’s risk of developing cancer, non-coding SNPs are relatively common in the population but only slightly increase cancer risk.

The team analysed whether there was a correlation between the presence of a particular SNP and the expression of particular genes.

In total, they looked at over six million genetic variants across 13 different body tissues.

Genetic
The researchers believe that understanding how non-coding DNA affects the development of this disease could one day improve genetic screening for cancer risk. Pixabay

They found that variations in the regions that regulate the expression of oncogenes and tumour suppressor genes affect cancer risk.

The study also revealed that these cancer-risk SNPs tend to be specifically located in regions that regulate the immune system and tissue-specific processes — highlighting the importance of these cellular processes to the development of cancer.

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“While minor genetic changes only have a small impact on cancer risk, the variations analysed in this study are numerous and common in the population,” said Emily Farthing, senior research information manager at British charity Cancer Research UK. (IANS)