week 3 Analogy and Homology
1.) Homologous traits
A. Briefly describe the two different species that
possess the homologous trait.
The two species that possess a homologous trait are
a dolphin and human. The trait they share is a similar bone structure in the
pectoral fin and human arm that consists of the humerus, ulna, and phalanges.
B. Describe the homologous trait of each species,
focusing on the differences in structure and function of the trait. Why do these homologous traits exhibit
differences between the two species? Make
sure your explanation is clear and complete.
Although they have similar structures, they do
not have the same function. Dolphins’ pectoral fins are used to steer them
through water and for balance. While humans arms are used for things such as
lifting and climbing. Another difference between the two is the bone structure,
fins have a compact structure while human arms have a longer and more spread
out structure.
The common ancestor of the dolphin and human is an
amphibian. The ancestor possessed this trait because they have the same
five-digit limb structure.
D. Provide an image of each species in this
comparison:
2.) Analogous traits
A. Briefly describe the two different species that
possess the analogous trait.
A butterfly,
who is an insect, possess the analogous trait of a bird. They are both have
wings which allow them to fly.
B. Describe the analogous trait of each species,
focusing on the similarities in structure and function of the trait. Clearly explain why these analogous traits
exhibit similarities between the two species.
The two species do not share the exact same
structure because the butterfly’s wings are made up of veins and scales while
birds wings are made up of feathers. Although the structure is not exact, they
share the function of flying because of the shared trait of wings.
C. All pairs of organisms share some common ancestor
if you go back far enough in time. Did
the common ancestor of these two species possess this analogous trait? Why or why not?
The common ancestor of the bird and butterfly was a
reptile. The common ancestor did not possess the analogous trait because it did
not have wings and was unable to fly.
D. Provide an image of each species in this
comparison.
Your images aren't visible. You need to upload them into the post, not just post the link. If you need help with this, there is a "Help" page on the course blog or you can email me.
ReplyDeleteThe opening prompt for both sections specifically ask for descriptions, not just identifications, of your two species. Expand and provide your readers with a better foundation of understanding for these comparisons.
Are the structures of the dolphin fin and the human arm the same?
http://1.bp.blogspot.com/-s1bQopgKHLg/UPZI_S07M8I/AAAAAAAAAAk/RO3uGaSBweA/s1600/dolphin_human_forelimb_300w.jpg
The bones have the same name and share a common origin, but the structure is most definitely NOT the same and this needed to be part of the discussion. The bones have changes in both humans and in dolphins from that common quadrupedal terrestrial mammalian ancestor and that is due to functional differences. Yes, there are functions are different. How does that impact their structural differences? This is another reason why the images needed to be visible, to show your reader these structural differences.
Since both dolphins and humans are mammals, do we really need to go back to amphibians to find a common ancestor? Wouldn't the common ancestor just be an archaic mammal? And we know from the fossil record that early mammals possessed the archaic skeletal limb structure and passed it on to these two descendants. That's what we need to know to confirm homology.
The second section of the analogy section asked you to focus on the similarities in structure and function, but you focus most of your effort on differences. We are trying to understand how functional/environmental pressures can produce similar solutions without a common genetic ancestry.
No, you have to go back much, much farther to find the common ancestor between a bird and a butterfly. It is difficult to guess at what the common ancestor of the bird and butterfly looked like some 100's of millions of years ago... it may have possessed wings or it may not have, but fortunately, we don't need to know that to confirm that these traits are analogous. While it is possible that the butterfly inherited its wings from that common ancestor, what about the bird? We know quite a bit about bird and bird-wing evolution. Birds evolved wings as they split from reptiles, and this occurred long, long after the split with that common ancestor with the butterfly. This means bird wing evolution occurred independently from that common ancestor with the butterfly. That is sufficient to confirm that these are not the product of common descent and are indeed analogous.