“The laboratory house mouse has maintained a standard 40-chromosome karyotype—or the full picture of an organism’s chromosomes—after more than 100 years of artificial breeding,” said Li Zhikun, a researcher at CAS’s Institute of Zoology.
“Over longer time scales, however, karyotype changes caused by chromosome rearrangements are common. Rodents have 3.2 to 3.5 rearrangements per million years, whereas primates have 1.6,” added Li, co-first author of the study.
The mouse, known as Xiao Zhu, or “Little Bamboo,” was the world’s first mammal with fully reprogrammed genes, according to the South China Morning Post.
The study claims to have provided important insight into how chromosomal rearrangements may affect evolution by showing that chromosome-level engineering is possible in mammals and by effectively deriving a laboratory house mouse with a novel and sustainable karyotype.
According to Li, such small changes can have a big impact. Humans and gorillas are separated by 1.6 changes in primates. Gorillas have two distinct chromosomes, whereas humans have two fused chromosomes, and a translocation between ancestor human chromosomes resulted in two distinct chromosomes in gorillas.
Individually, fusions or translocations can result in missing or extra chromosomes, as well as diseases like childhood leukemia.
While the chromosomes’ consistent reliability is useful for understanding how things work on a short time scale, Li believes that the ability to engineer changes could inform genetic understanding over millennia, including how to correct misaligned or malformed chromosomes.