Y chromosomes of gorillas could answer questions about male infertility

A new DNA-sequencing method has been developed, which has been used to determine the sequence of the gorilla Y chromosome.

The method is faster and cheaper than current sequencing techniques, and the researchers say that it could enhance the study of male infertility conditions and male-specific mutations.

The Y chromosome only makes up 1-2 percent of the genetic material in the cells of males and is extremely difficult to sequence. This is because of its small size and the fact that it is only present in a single copy whereas other chromosomes are found in pairs.

To reduce the difficulty in sequencing the researchers used a technique called 'flow sorting', which detects the chromosomes' size and genetic content and preferentially selects the Y chromosome for sequencing.

'Flow sorting increased the amount of the Y chromosome in our dataset to about 30 percent,' said lead author Professor Paul Medvedev, at Penn State University, Pennsylvania. Professor Medvedev and his team then used a computational technique called RecoverY to sort the data into Y and non-Y sequences based on the frequency of similar sequences.

Another reason why the Y chromosome is difficult to sequence is that it is composed of an unusually high proportion of repeated DNA sequences. The researchers therefore used a combination of two different sequencing technologies to determine the sequence of the Y chromosome.

The first method produced high quantities of short sequences of about 150 to 250 bases in length. Regions of overlap in these short sections of DNA were used to piece the sequences into longer sections. This short-sequence data was then compared with a second method which produces sequences of about 7000 bases.

The new approach was used to successfully sequence the Y chromosome of a male gorilla. The research also found that the Y chromosome of the gorilla is more similar to the human Y chromosome than to the chimpanzee Y chromosome.

'Our hypothesis is that this unusual similarity in the architecture of the Y chromosome between humans and gorillas might be driven by similar mating patterns,' Professor Kateryna Makova, study co-author at Penn State, told the Telegraph. 'For female chimpanzees, it is very common to mate with multiple males, but both human and gorilla females usually just mate with one male.'

Professor Makova believes that the findings could be important for research into male infertility.

'Some of these similar genes have been involved in male infertility in humans. So it is possible that some of the genes may be related to infertility disorders,' she said. 'This condition of infertility could be predating the split of humans and gorillas. We believe that, as a result, we certainly can provide additional information on the causes of infertility in some males.'

The new method may also aid conservation efforts as the ability to quickly and cheaply sequence the Y chromosome could help trace gorilla paternity and population migration within endangered species.

The study was published in the journal Genome Research.