It's hard to believe, given the great diversity of species, but all mammals in the world have come from a common ancestor that existed about 180 million years ago, and an international group of researchers has been able to reconstruct the genome of this animal using computer technology, which can help to understand the evolution of mammals and to preserve modern animals.
Definition of Cariotypes and Synthetic Relations
Previous studies of the evolution of mammal chromosomes have focused on placental or bagged mammals, which have led to a better understanding of some of the mechanisms that manage chromosomal transformations and their role in adaptation and formation, but many questions remain unanswered, in particular those relating to the preservation of large blocks of homologic synthesis and the distribution of break points, which is why researchers have taken up the reconstruction of the ancient cariotypes in mammalian philogenesis, including the cryotype of their common ancestor.
The gene blocks needed to develop the embryo
They used high-quality genomic sequences of 32 living species, representing 23 of the 26 known mammals — 19 plasma mammals, 3 bagged species, and 1 single-passed mammal.
These species included people, chimpanzees, vombats, rabbits, lamantins, livestock, rhinoceros, bats, pangolines, etc. The team also included the hen genomes and Chinese alligator for comparison, some of which were created by the Earth BioGenome project and other similar large-scale efforts to sequence the biodiversity genome.
Three different reference genomes representing the phylogenetically different superorders of mammals were used to estimate the deviation of reference data in reconstructed ancient cariotypes.
Reconstruction shows that the ancestor of all mammals probably had 19 pairs of autosomal chromosomes.
The team also identified 1,215 units of genes that constantly appear on the same chromosome and in the same order in all 32 genomes. These building blocks of all mammals' genomes contain genes that are needed to develop a normal embryo, said Damas.
Incredible stability over 300 million years
These synthetic segments are the fundamental building blocks of all mammals' genomes.
The nine smallest chromosomes are common to the common ancestor of all amniots, three of which have been retained by modern mammals. In other words, the ancestor of mammals had chromosomes with the same gene order as the chromosomes of modern birds. This discovery demonstrates "the amazing persistence of synths for about 320 million years of spinal evolution", the team notes.
The regions between blocks of conservative genes contained more repetitive sequences and were more exposed to the fractures of sequences, adjustments and duplications, which are the main drivers of the evolution of the genome.
Researchers have found that the difference between the chromosomes of mammalian ancestors and terium is the most recent common ancestor of the three lines represented in the reference genomes: its cariotype evolved from the cariotype of the ancestor of Teryans as a result of 124 chromosomal adjustments in 53 million years.
By tracking the chromosomes of the ancestors back in time from the common ancestor, researchers found that chromosomes' adjustment rates varied between mammalian lines; for example, in the line of gum animals, there was an accelerated transformation 66 million years ago when an asteroid struck dinosaurs and caused mammals to appear.
Thus, the results of this study will help to understand the genetic mechanisms that have allowed mammals to adapt and thrive on our planet over the past 180 million years.