Reproductive capacity is a fundamental trait of living things, and finding out how it has evolved and how it works at the genetic level is of great interest to evolutionary biologists. During the beginning of the development of an embryo, the cells divide into two main types, germ and somatic. Germline cells are housed in the reproductive organs and contain all the genetic information that is passed on to the next generation through gametes, while somatic cells make up the rest of the body. Biologists have discovered that, in some organisms, certain genes and repetitive DNA sequences are removed when cells are determined to be somatic, which means that not all cells in these organisms contain genomes with the same genetic content.
In some species the difference involves complete chromosomes that are restricted to the germ line, as is the case with zebra finches, where this chromosome has been called GRC (from the English “Germline-restricted Chromosome”). For the first time, an international team of researchers, in which members of the Genetics department of the University of Granada, has carried out a comprehensive genomic, transcriptomic and proteomic analysis of GRC in zebra finches. GRC is the largest chromosome in the genome of this species and constitutes more than 10 percent of its genome.
“GRC is a very strange chromosome. We found that some of their genes repeat dozens or even hundreds of times, while somatic cells only have one copy, “he says. Cormac Kinsella, one of the first authors of the study.
By identifying specific genes and comparing them with genomic data from other species, these researchers have been able to unravel the evolutionary history of GRC. Their results have shown that this chromosome originated tens of millions of years ago and is probably present in all songbird species, which account for half of bird species. They also think that GRC became an important factor in bird development because it contains many genes associated with the onset of embryonic development. Because it is not present in somatic cells, the expression of its genes only affects germline cells, thus protecting somatic cells from possible negative effects.
“Because we found expression of GRC gene content at RNA and protein levels, as well as evidence that natural selection acts on its genes, we hope this will be the starting point for new fascinating discoveries,” he says. Francisco Ruiz-Ruano, the other first author of the study and member of the University of Granada during its development.
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