According to the latest research, female's eggs are able to select sperm with the best genes to ensure the healthiest offspring. Semen does not appear to have the same ability to detect bad genes, this shows that fertilisation is not random and specific pairings between certain eggs and sperm are more common than others. Researchers bred female mice carrying one normal and one mutant copy of a gene that increased the chance of getting testicular cancer.
The resulting offspring followed Mendel's rules and there was a random dispersal of the mutated form among offspring. Researchers reversed the breeding- gave males the mutant copy of the cancer gene while the females had the normal version. Only 27 per cent of the offspring had the mutant variant, compared to the 75 per cent. Researchers found no evidence the mutated mice embryos were dying shortly after fertilisation, rather they were never fertilised.
The rate of metabolism folic acid - which is an important signalling molecule - is different in sperm and eggs. Research has revealed that these molecules play an important role in fertilisation. Changes in these signals may impact how much sperm and egg are attracted to one another. When sperm from multiple males arrive at an egg concurrently, eggs are able to choose the sperm whose recognition proteins are best suited for healthy fertilization. This selection process can spur the evolution of new recognition proteins, eventually resulting in reproductive isolation and, in some cases, the creation of new species altogether.
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