|
|
|
 |
|
|
Genomics at the Museum
The Real Bluegrass
Dr. Lynn Gillespie is using DNA to study the relationships
of different plants species to one another.
Dr. Lynn Gillespie, Annie Archambault and colleague Rob Soreng
of the Smithsonian Institution, Washington D.C., are studying
plants of the genus Poa, a type of grass commonly
known as bluegrass. There are more than 500 species of Poa
around the world. In Canada, there are more than 40 species,
such as the native Arctic bluegrass (Poa arctica)
and the cultivated Kentucky bluegrass (Poa pratensis)
of your lawn. They have sampled the DNA of numerous species
of Poa and related genera to examine their relationships.
By sequencing the same section of the chloroplast DNA (cpDNA)
in the different plants, they were able to detect mutations
represented by differences in single bases in the sequence,
or by deletions of small pieces of it.
|
|
| |
 |
|
| |
Plant cell drawing.
In a plant cell, DNA can be found in the nucleus, and in two
of its organelles,
the mitochondrion and the chloroplast. The chloroplast DNA
is smaller and simpler than nuclear DNA, making it a widely
used molecule in plant systematic studies. |
|
| |
|
|
|
| |
|
|
Numerous differences represent a high accumulation
of mutations, and suggest that species might have separated
a long time ago, and therefore might be classified in
different genera. Smaller differences distinguish species
within the same genus.
| |
 |
|
| |
 Poa arctica.
|
|
| |
|
|
|
C
|
C
|
G
|
A
|
G
|
A
|
G
|
T
|
T
|
|
|
|
G
|
G
|
T
|
T
|
C
|
A
|
A
|
| |
 |
|
| |
Poa abbreviata.
|
|
| |
|
|
|
C
|
G
|
G
|
T
|
G
|
A
|
A
|
T
|
T
|
C
|
T
|
T
|
G
|
A
|
T
|
C
|
C
|
A
|
A
|
| |
 |
|
| |
Poa glauca.
|
|
|
C
|
A
|
G
|
T
|
G
|
A
|
A
|
T
|
A
|
C
|
T
|
T
|
G
|
A
|
T
|
C
|
C
|
A
|
A
|
As you can see by comparing the sequences above, Poa
abbreviata and Poa glauca are closely
related, as two first cousins are, while Poa arctica
is a distant cousin.
Poa evolutionary tree
This is the evolutionary tree for a representative
sample of the genus Poa. An evolutionary tree
shows the relationships of different species to one
another. Lineages that diverge near the base of the
evolutionary tree are distantly related (see blue vs
red lineage). Species that group together at the top
of the evolutionary tree are closely related (in green).
The Pucciphippsia Story
Pucciphippsia, a tiny Arctic grass,
was only collected twice in the Canadian Arctic
in the 1920s and the 1950s. For many years, researchers
had not been able to locate this grass until Lynn
spotted it again in 1999 and 2000 at several different
locations in the Arctic. This plant had been classified
alternatively as a member of the genus Phippsia
and the genus Puccinellia, or as a hybrid
between the two genera. By examining the DNA of
the plant's chloroplasts, Lynn was able to confirm
that it was in fact a hybrid between Phippsia
algida and Puccinellia vahliana,
hence the name Pucciphippsia.
|
| |
 |
|
| |
Lynn Gillespie pressing plants on Axel Heiberg
Island.
Lynn Gillespie is a Botanist in the Research
Services at the Canadian Museum of Nature.
She specializes in the flora of the Canadian
Arctic and in the molecular systematics
of vascular plants. |
|
| |
|
|
|
| By comparing the banding patterns of the three
plants obtained by cpDNA restricted fragment analysis,
we see that Pucciphippsia plants can
have either the Puccinellia or the Phippsia
cpDNA banding pattern. Since cpDNA is inherited
only from the maternal parent, this shows that
both genera contribute to the genetic make-up
of Pucciphippsia.
|
| |
|
|
| |
 |
|
| |
DNA banding pattern.
|
|
|
|
|
|
|
|
|
|
