Gene expression in alligators suggests birds have thumbsOctober 4th, 2008 - 2:22 pm ICT by ANI
Washington, Oct 4 (ANI): By examining the expression of a particular gene in alligators, biologists have found that birds also have thumbs.
The research was conducted by Alexander Vargas and colleagues at Yale University, the University of Wisconsin-Madison and Yale Peabody Museum of Natural History.
Bird wings only have three fingers, having evolved from remote ancestors that, like humans and most reptiles, had five fingers.
Biologists have typically used embryology to identify the evolutionary origin (homology) of structures. The three fingers of the bird wing develop from cartilage condensations that are found in the same positions in the embryo as fingers two, three and four of humans.
However, the morphology of the fingers of early birds such as Archaeopteryx corresponds to that of fingers one, two and three in other reptiles (thumb, index and middle finger).
The fossil record clearly shows that fingers four and five (ring and pinky finger) were lost and reduced in the dinosaur ancestors of birds.
Further, the lack of expression of the HoxD-11 gene in the first finger of the wing makes it most similar to finger one (the thumb) of the mouse, consistent with comparative morphology.
However, the mouse is only distantly related to birds. Crocodilians, in turn, are birds closest living relatives.
To see whether the evidence from mouse HoxD-11 expression held up, Vargas and colleagues, working at the lab of Gunter Wagner at Yale, have examined the expression of this gene in alligators.
They found the expression to be, as in mice, absent only in finger one (the thumb).
Developmental and evolutionary biologists are familiar with the phenomenon of homeotic transformations, in which one structure begins to develop at a different position within the body.
A famous example is the case of the fruitfly mutant antennapaedia, which develops legs on its head instead of antennae.
The new work by Vargas et al. rekindles the hypothesis that a hometic frameshift occurred in the evolution of the bird wing, such that fingers one, two and three began to develop from the embryological positions of fingers two, three and four. (ANI)
- Genetic parasites changed pregnancy in mammals - Sep 27, 2011
- Gene loss could help explain evolution of limbs from fins - Jun 24, 2010
- Ring finger length linked to male libido - Sep 06, 2011
- Single gene acts as 'master organizer' of motor neurons in spinal cord - Sep 09, 2010
- New genes are as essential for life as ancient ones: Study - Dec 17, 2010
- Gene mutation behind brain size and shape identified - Apr 29, 2011
- Alligator found in a Brampton home backyard - May 24, 2012
- Searching for cannabis, British cops come across alligator - Jun 20, 2012
- New Evolution Theory Published In "Biology Letters" Questions Charles Darwin's Theory Of Evolution - Aug 25, 2010
- Primates better adapted to environmental changes - Dec 03, 2010
- Indian-origin researcher challenges Darwin's 'survival of the fittest' theory - Aug 24, 2010
- Neanderthals were more promiscuous than modern humans - Nov 03, 2010
- Scientists discover new mammal that lived 123 million years ago in China - Oct 09, 2009
- Alligator chomps off hand that fed it - Jul 30, 2012
- Ultraviolet pigment gives butterflies ability to identify own species - Feb 17, 2010
Tags: bird wing, bird wings, comparative morphology, dinosaur ancestors, early birds, evolutionary biologists, evolutionary origin, five fingers, fossil record, gene expression, gunter wagner, museum of natural history, peabody museum, peabody museum of natural history, pinky finger, three fingers, thumb index, university of wisconsin madison, yale peabody museum, yale university