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Understanding the Y Chromosome

written by: Balachandar Radhakrishnan•edited by: Paul Arnold•updated: 5/8/2009

Among human beings the phenomenon of sex determination is the province of a special pair of chromosomes called the sex chromosomes. These are termed X & Y chromosomes. Let's take a look at the Y chromosome and understand it in more detail.

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    Brushing up the Basics

    As we know Homo sapiens or human beings are made from the information encoded in their genetic map which is written with DNA. This DNA is then converted into mRNA and then into protein to make the building blocks of the body. The information molecule, the DNA, is tightly packed into structures called chromosomes which are responsible for carrying over the information from the parent to the offspring. Humans have 23 pairs of chromosomes which contain all information required for the creation of an offspring. Out of the 23 pairs of chromosomes the sex chromosomes X & Y determine the sex of an embryo. If a child inherits XX, then it is a female, and if it inherits an X and a Y then it is a male.

    c7.15.X.Y 
    Source: http://www.bio.miami.edu
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    The Y Chromosome

    The Y chromosome has been sequenced and has provided valuable insights into sex determination and the evolution of human beings as a whole. The Y chromosome is made up of some 58 million base pairs and more than 95% of it is male specific. The Y chromosome makes up almost 2% of the total DNA in a cell. Scientists believe that the modern Y chromosome evolved from the autosomes and slowly specialized into functioning as a sex determining agent.

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    Sex Determination

    The Y chromosome contains around 70 to 200 genes that are mostly involved in sex determination and the development of the male reproductive system and sexual characteristics. For about the first 40 days after conception the gonads of male and female embryos are the same, the reproductive system is undifferentiated. It is the presence or the absence of the SRY gene (sex determining region of the Y chromosome) that determines which way the embryo will develop. The gene encodes a protein called the testis-determining factor.

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    The future of the Y Chromosome

    It has also been shown that regions of the Y chromosome are constantly being lost by either deletions or recombination which might - so some scientists believe - eventually wipe out the male species from the human race. Although such genetic happenings are common on the Y chromosome, scientists have also identified regions which contain palindromic sequences which seem to help the Y chromosome retain its active functions.

    The Y chromosome serves as an evolutionary tracker since it is mostly conserved and transmitted from male to male offspring, this helps us make phylogenetic studies and identification of ancestry.

    Recommended Reading:

    http://www.nature.com/nature/journal/v423/n6942/full/nature01722.html

    http://ghr.nlm.nih.gov/chromosome=Y