Sex Chromosome Cross Over May Occur More Often Than Previously Thought

Sex chromosomes undergo division like all other cells but something makes them stand out from other chromosomes. Sex chromosomes X and Y switch only pieces of themselves when they cross over. It is this phenomenon that is responsible for individual variations between different people, even siblings.

A recent study done at the Arizona State University was led by Melissa Wilson Sayres, assistant professor in the School of Life Sciences and member of the Biodesign Institute's Center for Evolution and Medicine. This study was then published in the early online edition of the journal Genetics. It found out that the process of crossing over occurs much more often than was previously thought. The study has helped answer crucial questions about the diversity of the human race and sex chromosomal disorders.

DNA Cross-Over Is Limited: Myth Busted

The research team analyzed the DNA sequences of X chromosomes taken from 26 unrelated females. They found out that the genetic diversity was far greater in a certain area of the sex chromosomes named PAR1 (the region of X chromosome that crosses over) as compared to the other regions of the X chromosome.

It was expected that this greater range of diversity in the PAR1 region of X chromosome would suddenly drop “like a cliff” upon transition with other regions. What the researchers observed was that this genetic diversity had a slow “rolling hill” pattern. This transition area was found to be quite fuzzy and might be responsible for various sex linked disorders.

Previously, it was thought that there is a strict recombination boundary that put a limit on the swapping between the X and Y. Contrary to the popular belief, the evolution of the human genome over millions of years resulted in bit by bit “inversion” of the Y chromosome. Over time, the sex determining region of the Y chromosome (SRY), that determines the gender of an individual, has come to lie right next to the boundary.

The close proximity of SRY to the boundary region can result in hopping of the SRY over to the X chromosome which increases the chances of sex linked disorders, for example, de la Chappelle syndrome (SRY positive XX males), Turner syndrome (a single X chromosome in females rather than XX chromosomes), Klinefelter Syndrome (males with an extra X chromosomes-XXY), Swyer Syndrome (the person is genetically male with a weak XY chromosomal pattern but develops ovaries too).

READ Women Think Skinny Equals Happiness

During the course of this study, the researchers found 24 additional genes located within PAR1 and numerous others near the PAR1 boundary. These genes are important regulators of bone growth and melatonin production. These genes are also profoundly associated with psychiatric disorders, including bipolar affective disorder

The Future Implications

This study has made the made the blurry lines of human sex chromosome crossing over even blurrier. This study has prompted further research about how this frequent cross over is contributing towards the prevalence of sex linked disorders in humans.

According to Melissa Wilson Sayres, understanding the evolution of the X and Y chromosomes is imperative in order to understand the differences in the genetics of sex determination.

First Happiness Genes Found

Human genome is one of the most deeply studied subjects. For years, scientists have been trying to identify genes that are responsible for controlling various moods and their intensity in humans. Recently, researchers have isolated certain genes that are linked to happiness. This discovery can be the answer to how various humans experience happiness and how the level of happiness is regulated.

This discovery was done in a large scale study carried out in Amsterdam by professors Meike Bartels and Philipp Koellinger in over 298,000 people and was later published in the journal Nature Genetics. The study was done in collaboration with the Social Science Genetic Association Consortium.

The Happy Genes

Previous studies done by obtaining data of twins and families from the Netherlands Twin Register and other sources indicate that happiness depends, to a large extent, on the genetic makeup of an individual. These studies were, however, limited by their sample size.

This study was the first and the largest of its kind and included 181 scientists from 145 institutes, including medical centers in Rotterdam, Groningen, Leiden and Utrecht, and the universities of Rotterdam and Groningen.

The study subjects were assessed for three phenotypes- subjective well-being, depressive symptoms and neuroticism. The studied resulted in isolation of three variants of the genes that explain why level of depression varies among different people. The location of these genes was also deemed important. Eleven regions on the human genome were found to be associated with different degrees of neuroticism. Three variants for subjective well-being and two for depressive symptoms were identified.

It was discovered that the happiness genes are mainly expressed in the central nervous system, the adrenal glands and the pancreas. This study shows that happiness and depression overlap to a great extent.

The Future Prospects

This study has paved way for further research on the individual difference in happiness levels and the role of these genes in controlling the degree of happiness. It has proved to be a breakthrough for finding genes that are responsible for monitoring various moods in humans and is expected to prompt further research about different moods.

This study has opened doors for research on one of the most prevalent diseases of modern times-depression- to find out about genes that regulate depression. Policy makers have now started focusing on individual wellbeing since happiness and wellbeing play a key role in the physical and mental health of a person.

READ Sexual dysfunction and trying to conceive

According to professor Meike Bartels, this study has proven to be a groundbreaking one as it has helped determine the genetics of happiness by discovering three variants of the happiness genes. But still, there are a lot more variants to be discovered and this study was just the stepping stone.

Finding the location of these variants will play a key role in understanding the individual differences between people. It will also help determine why different people experience different level of happiness. It will help unravel the Nature’s secrets and the interaction between nature and the man’s environment and the impact of this interaction on the happiness level.