MadSci Network: Botany

Re: Do all plants have the same number of chromosomes?

Date: Sun Feb 15 20:03:53 2004
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1076889680.Bt

No, chromosome numbers vary widely among plant species. Arabidopsis thaliana, 
a model plant for genetic research, has just five chromosomes (2n=10). It is 
the first plant species to have all its chromosomes, or genome, sequenced. 

One of the highest chromosome numbers is 2n=240 in adder's tongue fern 
(Ophioglossum vulgatum). The lowest number known for a plant species is 2n=4 
in Shinners slender goldenweed
(Machaeranthera gracilis or Haplopappus gracilis).  

Many plant species and especially cultivated plant species are polyploid, 
meaning they have more than two sets of chromosomes. Tetraploid (4n), 
hexaploid (6n) and even octaploid (8n) species exist.

One way chromosome numbers increase is crossing of different species followed 
by spontaneous doubling. This is thought to be a mechanism in the origin of 
breadwheat, which has 42 chromosomes designated AABBCC. Einkorn wheat has 14 
chromosomes designated AA. Emmer wheat has 28 chromosomes designated AABB. 
Botanists looked for wild plants with 14 chromosomes and found several 
goatgrasses that could have supplied the BB and CC chromosomes. Then they 
crossed the goatgrasses with Einkorn and Emmer and were able to obtain 
breadwheat after doubling the chromosome number. 

Chromosome numbers can decrease by accidental loss of a chromosome(s) or 
merging of two chromosomes into one. Crepis species started with 6 chromosomes 
but species evolved with 5, 4 or 3 chromosomes. 


Arabidopsis thaliana

Chromosome Numbers of Selected Organisms

Karyotypes: Chromosome Numbers, Chromosome Shapes, and Phylogenetic 

Botanical Society of America's Statement on Evolution

Re: how do plants avoid fertilizing other plant species

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