Invasive Tumbleweed Demonstrates the Advantage of Extra Chromosomes

We don’t get Tumbleweed in this part of the world but for those of you who might see it as a nuisance, next time you see one….or maybe two tumbling across the road in harmony, then this research just might give you cause to look on in amazement and maybe bring some home with you. Worth keeping in mind is that nature loves diversity and only humans see it as broken.

The massive tumbleweed  Salsola ryanii is a species that was once thought to be going extinct. Researchers have found that this tumbleweed is more likely to expand into new regions, however, and is here to stay. This tumbleweed carries two copies of its parents’ chromosomes. While that’s been thought of as a biological advantage for plants, this work shows that the offspring can grow faster and larger than its parents. The findings have been reported in the journal AoB Plants.

Almost all mammals, including humans, are diploid organisms, which means they carry two sets of chromosomes; one set comes from the female parent, and one from the male. In humans, if an egg that mistakenly carries two sets of chromosomes is fertilized, the resulting zygote is unlikely to survive.

In plants, however, it’s far more common for organisms to carry more than two sets of chromosomes – called polyploidy. Many common domesticated crops like apples, peanuts, and wheat are polyploid. Polyploidy can easily occur when two parents have similar chromosomes or when there is a genome duplication event. It’s often been assumed to confer some biological benefit in plants, otherwise, polyploidy would be rejected and it wouldn’t be seen so often.

“Typically, when something is new, and it’s the only one of its kind, that’s a disadvantage. There’s nobody exactly like you to mate with,” explained study co-author Shana Welles, a graduate student at the time of this research who is currently a postdoctoral fellow at Chapman University.

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