Evolution and its genetic basis

Campbell and Reece, Chapter 22 - Descent with modification: A Darwinian view of life
and Chapter 23 - The evolution of populations
and Chapter 24 - The origin of the species
(also, I will jump about several chapters here)

Homology Limb TRANSPARENCY (Fig. 22.14)
Comparative anatomy, embryology, biochemistry, molecular biology
Homology - common descent
forelimbs:
bat (also pterodactyl, bird - fly)
whale (also seal - swim)
cat (also sheep - run)
human (also insectivore - grasp)

Divergent (vs. convergent evolution)
Phylogenetic tree TRANSPARENCY (Fig. 24.24) Horse evolution

TRANSPARENCY (Fig. 24.17) controversy
Gradual vs. sudden, gaps in fossil record, dramatic events

Drawings like this next one confuse the issue since butterflies (as if they were all from today's world) are drawn while the time line suggests that the ones at the bottom of the figure are obviously ancestral.

TRANSPARENCY (Fig. 24.6) speciation in the same area (sympatric) and in different areas (allopatric. There are also other isolating mechanisms.

STORY
Moths use sex attractant pheromones from female sensed by big feathery antennae in males.
These may be molecules like acetates, chains10 to 15 carbons long.
Two similar moths in same place (sympatric) do not mate, thus seem to be 2 species (Roelofs and Comeau, Science 165, 398-400, 1969).
One uses molecule cis around one double bond, the other trans.
For that to happen, one female would have to change pheromone used and a male at the same place and time would have to have a change in preference, an amazing jump (saltation).

Comparative anatomy, embryology, biochemistry, molecular biology
TRANSPARENCY (Table 22.1) - can use "molecular" (biochemical) data to get relationships (here amino acid differences in a part of hemoglobin).

TRANSPARENCY (Fig. 25.8) at the beginning of the semester, I did some hand waving about the relationship between phylogeny and taxonomy, and I do it again with this figure (professors are good at hand waving). While taxonomy and phylogeny are different, they are related in that more inclusive levels of taxonomy are related to a common ancester in phylogeny.

Remember (and it is so confusing that it is hard to remember) that lower on the diagram are ancestors, not "simple" organisms that are around today. One "left-over" that helps to confuse this issue is the old saying "Ontogeny recapitulates phylogeny." Gill pouches and tail suggest that people and birds go through a fish stage in their development.

Genetic basis of variability and selection
Remember, in the genetics outline, I said (and gave this quote from Mendel):
Mendel (knew about Darwin but Darwin did not know about Mendel)
"...this seems to be the one correct way of finally reaching the solution to a question whose significance for the evolutionary history of organic forms must not be underestimated."

TRANSPARENCY (Fig. 23.3B) The Hardy-Weinberg "theorem"
Hey, this looks like a punnet square for the F2 of a cross with one gene and two alleles, except here, we have added probabilities of the two alleles (p + q = 1) to get probabilities of the "4" genotypes (actually 3 since aA is the same as Aa)

"Adaptive significance," "selection pressures" and all those favorite jargons give the false impression that everything is the way it is because of "deliberate" outcomes of evolutionary processes. But all kinds of things got to be the way they are through "accidental" processes. (Furthermore, evolution cannot make an overall master plan but rather has to build on the successes and mistakes of the past.)

TRANSPARENCY (Fig. 23.4) Genetic drift The frequency of alleles might change by this seemingly accidental mechanism.

TRANSPARENCY (Fig. 23.5) The bottleneck effect. What if some catastrophe wiped out all but a few individuals? The population would likely lose a lot of its variability as shown in this figure.

Think about how the Hardy-Weinberg principle looks like a one-gene two-allele cross. Then remember how much ore complicated the F2 Punnet square looked for Mendel's second law than for his first. My gosh, what if there were more than 2 genes and 2 alleles? This is called polygenic inheritance.

TRANSPARENCY (Fig. 23.12) - selection depends on variability in population
This plot of Frequency as a function of some quantitative measurement of phenotype shows a normal distribution.
Artificial selection in experiments - Directional selection
Hirsch-Hadler maze to divide Drosophila into normal distribution
Selection for behavior (that was news at the time) - geotaxis or phototaxis.

METHODS

TRANSPARENCY (Fig. 25.13) There's a lot of work these days with DNA sequence, but similarities in certain stretches can only be made after adjusting for big changes (like gaps).

TRANSPARENCY (Fig. 25.UN1)Make a phylogenic tree using DNA

TRANSPARENCY (Fig. 25.17) Cladistics - compare how many differences there are with an outgroup.

SLU's Biology department well represented in evolution: Drs Aspinwall, Barber, Bernhardt, Mayden, and Wood.


Biology majors (BA and BS) in this department must take a course in evolution (BL A301).

This page was last updated 7/30/02

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