Songbirds have an unusual extra chromosome

Scientists have discovered that songbirds have an extra chromosome in their germ cells.

By Lewis White

May 9, 2019 at 7:00 pm

A new study, involving scientists from the Royal Veterinary College (RVC) in England and the Institute of Cytology and Genetics (ICG) in Russia, has found that all songbirds have an additional chromosome in their germ cells, unlike other avian species.

Somatic (or normal) cells have two copies of each chromosome, whereas germ cells (cells that become a sperm and an egg), typically have the same set of chromosomes as a somatic but only one copy of each.

The additional chromosome found in the germ cells of songbirds has been named the Germline Restricted Chromosome (GRC) and is not presented in their somatic cells.

Songbirds are the largest group of birds, meaning that nearly 6,000 of the 10,000 existing avian species have the GRC.

The GRC is transmitted to offspring from mothers and is discarded from all somatic cells of the offspring in the early stages of development. Males have the GRC but do not pass it on and it is removed from the germ cell before it becomes sperm.

The first GRC was reported in zebra finch more than 20 years ago, but it was considered a genetic oddity until this study.

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