Scientists find easy way to separate male and female SPERM

Sperm can ‘EASILY’ be separated into male and female as scientists warn the ‘concerning’ breakthrough could lead to a gel for at-home sex selection

  • Method was enveloped and proven on mice at the University of Japan 
  • The process could theoretically be applied to all mammals – even humans 
  • Allows X-chromosome carrying sperm to be slowed down and separated  
  • Experts say it is still in very early stages and poses disconcerting social issues and an ‘ethical minefield’  for potential sex-based discrimination in babies

Scientists have discovered a way to distinguish between male and female sperm, fuelling concerns of potential at-home kits and gels to determine the sex of a foetus.

Researchers at the University of Japan tested their sex-sorting method, which determines whether sperm carries an X or Y chromosome, on mice. 

The proof-of-concept experiment slows down X-bearing chromosomes – which would produce a female – and the different sex sperms can then be separated.  

It has restarted a debate around ‘designer babies’ with the process potentially one day being used to aid parents having a child of a specific sex based on social biases. 

‘I am concerned about the social impact of this,’ Alireza Fazeli of Tartu University in Estonia told the New Scientist.

‘It’s so simple. You could start to do it in your bedroom. Nobody would be able to stop you from doing it.’  

Scientists develop simple way to manipulate sex of offspring. The proof-of-concept experiment slows down X-bearing chromosomes – which would produce a female – and the different sex sperms can then be separated (stock)


Humans have two sex chromosomes, the X and the Y. 

These are carried in the sperm, with each sperm normally carrying one or the other. 

Generally, an X chromosome carrying sperm will produce a female and the Y chromosome sperm will produce a male.  

In humans, the 22 other pairs of chromosomes – the autosomes – are identical.   

The single chromosomes are inside sperm heads which fertilise eggs. 

All eggs have an X chromosome, making the sperm the sole determining factor of biological sex. 

Sperm is roughly half X and half Y chromosome carrying.   

Professor Allan Pacey, professor of Andrology at the University of Sheffield and former chairman of the British Fertility Society, said: ‘To date, the experiments have only been performed on the sperm from laboratory mice and we don’t know if this effect would be seen in the sperm from other animals, such as cattle (where producing more females is important for dairy herds) or in humans where would be parents may desire a child of a specific sex (although that is currently unlawful in the UK). 

‘However, the data does suggest that sperm are far more complex cells than we’ve previously been aware of and that we still have a lot more to learn about them.’ 

Most cells from male mammals contain both an X and a Y chromosome, but during sperm development (spermatogenesis) they are segregated into different cells.

This means an individual sperm will carry either one or the other, with an X chromosome giving rise to daughters and a Y chromosome to sons.

Researchers say that unlike the Y chromosome, which carries very few genes, the X chromosome carries many, some of which remain active in the maturing sperm.

This provides a theoretical basis for distinguishing the two, the research published in the journal PLOS Biology sets out. 

The study was performed in mice, but the technique is likely to be widely applicable to other mammals as well, including humans. 

Dr Peter Ellis, lecturer in Molecular Biology and Reproduction, University of Kent School of Biosciences, said: ‘It potentially allows for routine sex selection in any such species – however, I repeat that this is only conjecture at present and remains to be tested. 

‘Routine sex skewing in livestock animals would be a major boon with dramatic benefits for animal welfare in many species. 

‘Sex skewing in humans would be an ethical minefield with the potential for unpredictable and disruptive social consequences.’

Professor Masayuki Shimada, a co-author of the study, said: ‘The differential expression of receptor genes by the two sex chromosomes provides the basis for a novel and potentially highly useful method for separating X and Y sperm and we have already succeeded the selectively production of male or female in cattle and pigs by this method.

The method was developed on mice at the University of Japan where researchers created a simple way to determine between sperm bearing either an X or Y chromosome (stock)

‘Nonetheless, use of this method in human reproductive technology is speculative at the moment, and involves significant ethical issues unaffected by the utility of this new technique.’  

The researchers found 492 genes are active in only X-bearing sperm and 18 receptors that were good candidates for manipulating the sperm. 

They then focused on a pair of receptors and found that a chemical that bound to them slowed sperm motility without impairing either fertilisation ability or viability.

IT was found that this was due to impaired energy production within the sperm, causing them to slow down.   

Mouse sperm treated with the chemical, followed by in vitro fertilisation with the fastest swimmers, led to litters that were 90 per cent male.

When the slower swimmers were used instead, the litters were 81 per cent female.

Scientists say that while other procedures that can be used to separate X and Y sperm, they are cumbersome, expensive, and risk damaging the DNA of the sperm. 

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