Genome sequencing of cats and their kittens has shown that the sperm of older tom cats has more mutations, just like that of older human males. This may show evidence of a universal phenomenon in male animals.
鈥淥ur results suggest that this paternal age effect is general to mammals, and indeed anything that is producing sperm,鈥� says Richard Wang at Indiana University in Bloomington.
Each human is typically born with about 50 to 60 small mutations 鈥� such as a change in a single DNA letter 鈥� not found in the body tissues of their parents. These 鈥渄e novo鈥� mutations arise as sperm and eggs form. In people, 80 per cent of de novo mutations come from the sperm of the father, and older fathers pass on more than younger ones.
Advertisement
鈥淭here are some studies that have linked the number of mutations and paternal age with autism, schizophrenia and a number of other neurodevelopmental disorders,鈥� says Wang.
There is some evidence this is also the case in other primates. To find out if it happens in other mammals, too, Wang and his colleagues sequenced the genomes of 11 parent-kitten trios. They found an average of 70 per cent of mutations came from the tom cats, and the older the tom, the more mutations it passed on to its kittens.
The mutation rate per DNA letter per year is five times as high in cats as in people, the team found. However, because cats have offspring at a much younger age than people do, each kitten had only around 15 de novo mutations, says Wang.
The reason the number of mutations increases with age is that sperm production requires continual cell division in the testes, which leads to an accumulation of small mutations. Egg production, by contrast, isn鈥檛 continual. However, because eggs remain stuck in the last stage of cell division, chromosomal abnormalities 鈥� very large-scale mutations 鈥� are much more likely to arise in eggs than sperm. This can lead to conditions such as Down鈥檚 syndrome.
Reference:
