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There are many unknown facts and reasons behind male infertility. However, science is taking rapid strides in this field and the successful sequencing of the entire genome of individual sperm may prove to be a milestone in understanding male fertility.
In an important scientific breakthrough, scientists from Stanford University have been successful in determining the entire genome sequence of 91 human sperms of a single 40 years old man. His whole genome sequence (obtained from diploid cells) had already been studied previously. Comparing the genome sequence of the sperm with that obtained from the diploid cell provides a wonderful insight about the naturally occurring genetic variations in a single individual.

Almost all the cells of the human body contain a pair of 23 chromosomes and are therefore referred to as diploid cells. During the formation of sperms or eggs (male and female gametes respectively), a process of cell division, called as meiosis, takes place and as a result, the sperm or the egg contains only a single set of 23 chromosomes. They are therefore called as haploid cells. The fertilized embryo, formed as a result of the fusion of the sperm and egg, again contains a pair of 23 chromosomes.
During meiosis, a natural process called as recombination takes place which ensures that the embryo formed after fertilization contains a healthy blend of genes from all the four grandparents. During recombination, parts of the chromosome get shuffled and hence, the genetic sequence of each sperm varies slightly. Sibling variation can be attributed to the process of recombination.

The team of researchers, led by Stephen Quake from the Stanford School of Medicine’s Department of Bioengineering, was able to find out the entire genomic sequence of 91 sperms. They could analyze all the sites, from the possible 1.2 million positions in the DNA, where recombination took place. Apart from the “recombination hotspots” where re-combinations commonly take place, they were also able to find out that chromosomes in certain sperms recombined at totally unexpected places. The process of recombination, leading to genetic reshuffling, is unique to each sperm cell and leads to increased genetic diversity in children of the same parent. The researchers found 23 re-combinations in the sampled sperm, along with 25 to 36 new mutations. The mutations varied from small to as big as missing of a full chromosome. Such mutations can render a sperm incapable of fertilizing an egg and be an important cause behind male infertility.

The researchers feel that future research into the genomic sequencing of a sperm can help us to understand many other causes that may be leading to male infertility. The results of the present study have been published in the July 19 online issue of the journal ‘Cell.’
Continue reading after recommendations

  • “Genome-wide Single-Cell Analysis of Recombination Activity and De Novo Mutation Rates in Human Sperm”, by Stephen R. Quake et al, published in the July 20, 2012 issue of the journal Cell, accessed on August 19, 2012.
  • “Sperm sequencing could help fight infertility”, by Jessica Hamzelou, published in the July 19, 2012 issue of the NewScientist, accessed on August 19, 2012.
  • “Sequencing of Single Sperm Could Reveal New Infertility Causes”, by Katherine Harmon, published on July 19, 2012 at, accessed on August 19, 2012.
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