'Weird' shift in falcon genomes in line with mammals

A study led by researchers from New York University Abu Dhabi (NYUAD), UAE, has sequenced the genomes of eight falcons – peregrines, gyrfalcons, saker falcons, lanner falcon and the common kestrel – to advance understanding of how this culturally prized group of birds evolved, which could shed light on the genomic evolution of mammals.

While the majority of bird species have around 41 pairs of chromosomes, falcons only have around 25 pairs. Falcons also have much less variety in the size of their chromosomes and no small chromosomes. It is thought that smaller chromosomes – called microchromosomes – fused with larger chromosomes millions of years ago. 

Mammals are similar in that they have relatively few chromosomes and no small ones. “There are some weird things happening in mammal genomes and some people say it's because all these chromosomes got lost 300 million years ago,” says Justin Wilcox, from NYUAD. “I wanted to see if that was happening in falcons after they lost their chromosomes.”

One of these ‘weird things’ is a shift over time in the ratio of the amino acid pairs – adenine, thymine, guanine and cytosine – that form the backbone of DNA in mammalian genomes towards more adenosine and thymine, and less guanine and cytosine. The study saw a similar shift in falcons, but not in other birds.

The genomic analysis suggested that this loss of guanine and cytosine was most evident in chromosome sections that contained the fused microchromosomes, and in regions of the chromosome involved in a process called DNA methylation, which is vital for regulating gene activity.

The newly sequenced genomes will provide a treasure trove of data for researchers seeking to understand genome organisation ,and how it compares between different groupings of animals, says Alexander Suh, a biologist at Uppsala University in Sweden, who was not involved in the study. 

“When we look at very discrete patterns, like the standard bird and the standard mammal, how did it get to that point,” Suh says. “The falcons are a nice starting point to think about those terms.” 

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