Biology
Evolution
Major Mechanisms of Change
EvoDevo : A new branch of science that looks at ways species have evolved by mutating “master control genes.”
Introduction : In your study of genetics, you learned that genes code for our traits in the form of proteins. Some genes don’t make protein though. These genes control other groups of genes (a suite of genes) and are similar to a master switch that controls many other switches. They not only determine when during development the switch turns on or off but also how many times it turns on and off and how long it stays on before turning off. The next activities will let you examine a couple of examples of EvoDevo in action.
Choose from the following descriptions of master gene activity whenever you are asked to describe what is happening with the master gene. a) Turns on and off twice to repeat the process. b) Turns on high at the head end during development, then dials down the rate in the head and dials up the rate to the body at birth and as the child grows c) Turns on and delays the turn-off time compared to its ancestors d) Turns on during development but proceeds at a much slower rate than in ancestors.
Station #5 : Meter stick
Use the meter stick to determine your overall height. Then determine the height of your head only. Divide you head height by your body height. Record here. _______
These are the same measurements for a six-week old. ___cm head/ ___cm overall = _____
1. How do the two measurements compare?
Now, use the infant’s ratio and multiply it by your overall height.
2. How big would your head be if you had the same proportions as an infant?
Human infants have an antero-posterior gradient of growth. In other words, when they are born, babies have a big head relative to their bodies. As children get older, the growth rate of the head (anterior end) slows and the body (posterior end) catches up.
3. What is going on with the master gene to make this happen? Circle one. a) b) c) d)
Paedomorphosis: Evolving by retaining the juvenile features of ancestors.
Station #8 : Fetal and adult skulls of chimpanzee ( Pan troglodyte s) and human ( Homo sapien sapiens ).
Compare the skulls carefully.
4. Which skull(s) has(have) the most similar proportions or shape?
5. Which skull(s) is(are) most different?
6. Which adult, the chimp or the human, has a skull shape that is the same as the fetal skulls?
7. Using the concept of paedomorphosis, explain how humans could have evolved big brains.
8. What is going on with the master gene to make this happen? Circle one. a) b) c) d)
Mrs. Loyd
 cschmittloyd@waukeeschools.org
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Station: Desk Work
Mammals of all kinds have the same set of bones in their forelimbs: one bone, two bones, lots of blobs, and digits. The digits and other bones are various lengths. For example, the digits of a cat are very short while the digits of a bat are very long.
9. Look at the diagram and explain what is happening with the master gene to make this happen.
Circle one. a) b) c) d)
At one point in history, a major adaptation converted fins (used by fish) into a simple arrangement of one bone, two bones, lots of blobs, and digits (see Tiktaalik).
Once it had this skeletal arrangement, repeating the process at a point further down the body resulted in organisms that were four legged (see Acanthostega).
Scientists have called it a fish-amphibian.
This was the ancestor to all four-legged organisms (tetrapods).
10. Look at the diagram and explain what is happening with the master gene to make this happen.
Circle one. a) b) c) d)
Mrs. Loyd
 cschmittloyd@waukeeschools.org
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Biology
Evolution
Determining Relatedness
Using shared derived characteristics to build a phylogenetic tree
Introduction: Evolution is all about the unity and diversity in life. The unity is shown by organisms sharing a common ancestor while diversity is shown by the branching and variation of life. Darwin was the first to view the history of life as a tree, with multiple branches from a common ancestral trunk to the descendant species at the tips of the twigs. Biologists represent these patterns of descent with an evolutionary tree, although today they usually turn the trees sideways.
An evolutionary tree is based on the Darwinian concept that evolution proceeds when a new heritable trait develops in an organism and it is passed on to its descendants. Groups of organisms that share this new, or derived, trait are more closely related to each other than to groups that have only ancestral traits. Therefore, they should be closer on the tree.
For example, a backbone is a derived trait shared by many animals and does not distinguish mammals from other vertebrates but they all share an ancient common ancestor who “invented” backbones. Invertebrates are not closely related to mammals because they do not share this derived trait and the branching occurred so long ago.
Look at the chart and tree. It illustrates that the sequence in which shared derived characters appear can be used to construct a phylogenetic tree. The common ancestor is not shown. It would appear above “Hair” It would most resemble an Iguana.
Use the following character table to fill in the evolutionary (phylogenetic) tree. Model your tree after the one given above.
Use the organisms’ names on the right-hand side and the shared derived characters on each branch.
CHARACTERS SHARK
Vertebrae
Two pairs of limbs
X
BULL-
FROG
X
X
KANGA-
ROO
X
X
HUMAN
X
X
Mammary glands
Placenta
X X
X
Mrs. Loyd
 cschmittloyd@waukeeschools.org
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SETS
1
TRAITS
Dorsal Nerve Cord (notochord)
Kangaroo Lamprey
Rhesus
Monkey
ANIMALS
Bullfrog Human
Snapping
Turtle
Tuna (fish)
X X X X X X X
2
Paired Appendages,
Vertebral Column
X X X X X X
3 Paired Legs X X X X X
4
Amnion
(Amniotic sac)
X X X X
5 Mammary Glands X X X
6 Placenta X X
7
Canine teeth short,
Foramen magnum forward
X
Total of X’s  5 1 6 3 7 4 2
Instructions: Use the “set” numbers from the table (representing shared derived characters) to label each diamond. Then use the animal names from the table to label each arrowhead.
Mrs. Loyd
 cschmittloyd@waukeeschools.org
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