Big chromosome discovery in larks

This video is about skylarks singing in Belarus.

From Lund University in Sweden:

Record-size sex chromosome found in two bird species

December 4, 2019

Researchers in Sweden and the UK have discovered the largest known avian sex chromosome. The giant chromosome was created when four chromosomes fused together into one, and has been found in two species of lark.

“This was an unexpected discovery, as birds are generally considered to have very stable genetic material with well-preserved chromosomes,” explains Bengt Hansson, professor at Lund University in Sweden.

In a new study, the researchers charted the genome of several species of lark, a songbird family in which all members have unusually large sex chromosomes. The record-size chromosome is found in both the Eurasian skylark, a species that is common in Europe, Asia and North Africa, and the Raso lark, a species only found on the small island of Raso in Cape Verde.

This 8 May 2018 video, in Portuguese with English subtitles, says about itself:

A new home for the Raso Lark

The Raso Lark (Alauda razae) is confined to the small Raso islet on Cape Verde and it is one of the most threatened birds in the world. Its small population was once reduced to less than 100 birds worldwide! To increase its chances of survival Biosfera 1 joined SPEA and DNA and, with the support of the MAVA Foundation, translocated 37 birds to the neighbour island of Santa Luzia.

The translocation was successful and now we wait for the first breeding signs of this new population.

The Lund University article continues:

“The genetic material in the larks’ sex chromosome has also been used to form sex chromosomes in mammals, fish, frogs, lizards and turtles. This indicates that certain parts of the genome have a greater tendency to develop into sex chromosomes than others,” says Bengt Hansson.

Why the two species have the largest sex chromosome of all birds is unclear, but the result could be disastrous lead to problems for female larks in the future. Studies of different sex chromosome systems have shown that the sex-limited chromosome, for example the Y chromosome in humans, usually breaks down over time and loses functional genes.

“Among birds, the females have a corresponding W chromosome in which we see the same breakdown pattern. As three times more genetic material is linked to the sex chromosomes of these larks compared to other birds, this could cause problems for many genes,” says Hanna Sigeman, doctoral student at the Department of Biology, Lund University.

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