Changing the number of chromosomes can take millions of generations to happen in nature, and now, scientists have been able to make these changes in lab mice in a blink of an eye.
The new technique using stem cells and gene editing is a major accomplishment and one that the team is hoping will reveal more about how the rearrangement of chromosomes can affect the way that animals evolve over time.
It's in the cells' chromosomes that we find our genes, which are passed on from one generation to the next.
Humans and mice have the same number of chromosomes. Sex cells are an exception.
Stem cells that are unfertilized are the best to start with. Lack of an additional set of chromosomes provided by a sperm cell deprives the cells of an important step in negotiating which genes in which chromosomes will be marked active to do the job of building a body
Engineers trying to restructure large chunks of the genome were stymied by this process.
The information about which genes should be active disappears in haploid stem cells, limiting their pluripotency and genetic engineering.
There were three naturally imprinted regions that were missing. The researchers fused two medium-sized chromosomes and two large chromosomes in two different orientations, resulting in three different arrangements.
Although breeding was slower than normal, the fusion of chromosomes 4 and 5 was the most successful.
The offspring from the fusion of chromosomes 4 and 5 were more anxious than the offspring from the 1 and 2 fusion.
The researchers say that the drops in fertility are due to how the chromosomes separate after alignment. It shows how important chromosomal rearrangement is to reproductive isolation.
After more than 100 years of artificial breeding, the laboratory house mouse has retained a standard 40-chromosome karyotype.
Karyotype changes are common over long time scales. Rodents have more than 3 rearrangements per million years.
Our own ancestors have had rare leaps in chromosomal rearrangement help direct their evolutionary path. Chimpanzees have chymosomes fused into one in their genomes.
Changes can happen once every few hundred thousand years. There are signs that the genetic edits made in the lab could have a dramatic effect on the animals.
It's still early days, but it's possible that there could be an opportunity to correct chromosomes in humans. Children's leukemia can be caused by chromosomal fusions and relocations.
According to Li, the chromosomal rearrangement event is the driving force behind species evolution and important for reproductive isolation.
The research has appeared in a journal.
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