Evolution and its genetic basis


Audesirk, Audesirk & Byers Selections from Chapters 14-16 & 18

Background and review

Figure 14-7
Homology Limb
Comparative anatomy, embryology, biochemistry, molecular biology
Homology - common descent
bat (also pterodactyl, bird - fly)
dolphin (also seal - swim)
dog (also sheep - run)
human (also shrew - grasp)

Figure 18-6
Divergent (vs. convergent evolution)
Phylogenetic tree
Eukaryote evolution

isolating mechanisms

Remember, species can reproduce

Figure 16-10
speciation in the same area (sympatric)

Figure 16-9
and in different areas (allopatric). There are also other .

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).

Divergent evolution

Figure 23-1
Comparative anatomy, embryology, biochemistry, molecular biology

Figure E18-1
can use "molecular" (biochemical) data to get relationships

Figure 14-11
also (cytochrome c sequence comparison between species)

Figure 24-1
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.

Figure 24-2
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.

Need to simplify by considering one gene

Box (a closer look) [p. 298, chapter 15]
The Hardy-Weinberg principle
(Orientation for next week's lab)

The Hardy-Weinberg principle describes the frequency of alleles if there is no change (a non-evolving population):
(1) large population
(2) no migration
(3) no net mutation
(4) random mating
(5) nonatural selection

I've redrawn Fig. 12-11 with p and q being the gamete probabilities in the population.
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)

Imagine you roll a die: Expectation - 1, 2, 3, 4, 5, and 6 each should occur 1/6 of the time. How deviant from that expectation would your outcome need to be for you to conclude that the die is "loaded?"

Restated with reference to our coverage of statistics and the scientific method, how far from expectation must the observed results be before you conclude that they show a real difference and not just chance, keeping in mind that you can never be absolutely certain?

In lab, we will simulate a sampling by selection and counting beads and thus doing the appropriate statistical test, called Chi-square

"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.)

Figure 15-5
Genetic drift
The frequency of alleles might change by this seemingly accidental mechanism.

Figure 15-7
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.

Figure 24-15c
Cheetah (very weak, genetically speaking, because of lack of heterozygosity in its genes)

Polygenic inheritance

Think about how the Hardy-Weinberg principle looks like a one-gene two-allele cross. Then remember how much more 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.

Figure 15-13
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."

Figure 15-13
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

Environment changes
variability important
what is adaptive at one time may not be at another time


Figure 14-11
There's a lot of work these days with DNA sequence,
Similarities in sequences of human and mouse cytochrome c

Figure E18-1
Make a phylogenic tree using DNA

Questions used in 2007 & 2008 elated to this outline

In a population of wild flowers, there is this frequency of flower color alleles: R (red, dominant) = 0.8, r (white, recessive) = 0.2. Which describes how the r allele might be eliminated if only a few individuals from each generation reproduce?
(a) the Hardy-Weinberg theorem
(b) selection pressure
(c) sympatric speciation
(d) sexual selection
*(e) genetic drift

Long ago, some wogglebugs blew over to an island (previously devoid of wogglebugs) from the mainland and now biologists cannot get mainland and island wogglebugs to interbreed. This is
(a) genetic drift.
(b) expected from the Hardy-Weinberg principle.
*(c) allopatric speciation.
(d) comparative embryology.
(e) the Punnett square.

What is the deal with the cheetah?
(a) It cannot produce fertile offspring.
*(b) It has low heterozygosity in its genes.
(c) Sex-attractant pheromone traps have been used to eliminate this pest.
(d) It has a notocord but not a vertebral column.
(e) It is an extinct ancestor to present lions and tigers.

In a population of omicrons, the frequency of alleles for brunette fur is 0.8 while the frequency for blond is 0.2. What is the proportion of heterozygotes?
(a) 0.8
(b) 0.64
*(c) 0.32
(d) 0.2
(e) 0.04

If the tallest guy and gal in the class got married and had kids and the shortest guy and gal in the class also got married and had kids, the first couple's kids might be taller than the other couple's because of
(a) the fact that ontogeny recapitulates phylogeny.
(b) sympatric speciation.
(c) the bottleneck effect.
*(d) polygenic inheritance.
(e) Mendel's second law.

Which of the following is NOT a condition of the Hardy-Weinberg Principle?
*A) Natural selection will occur.
B) No mutations occur.
C) No gene flow will occur.
D) All mating is random.
E) Individuals will not move into or out of the population.

A small population is likely to evolve because of ________, but this is not likely to be true for large populations.
A) artificial selection
*B) genetic drift
C) mutations
D) the Hardy-Weinberg Principle
E) natural selection

Imagine that a population of deer living on an island without any predators was threatened with overpopulation. Then wolves were imported. After a few years there were fewer deer, but their average running speed had increased. This is an example of
A) inheritance of acquired characteristics.
B) theraputic cloning.
C) genetic drift.
D) the Hardy-Weinberg principle.
*E) natural selection.

According to the Hardy-Weinberg Principle, if 3/4 of the alleles in the gene pool are A1 and 1/4 are A2, what fraction of individuals has genotype A1A2 in this population?
A) 1/4
*B) 3/8
C) 1/2
D) 1/16
E) none of the above

Natural selection acts on ________ to affect the evolution of ________.
*A) phenotypes; populations
B) genotypes; populations
C) genotypes; individuals
D) genotypes; mutations
E) phenotypes; individuals

The male peacock's beautiful tail is really a trade-off between
A) natural selection and genetic drift.
*B) sexual selection and natural selection.
C) the Punnett square and natural selection.
D) disruptive selection and natural selection.
E) the bottleneck effect and allopatric speciation.

The extreme loss of genetic diversity that has occurred in cheetah populations due to overhunting is the result of
A) the Hardy-Weinberg principle.
B) sympatric speciation.
*C) a population bottleneck.
D) pheromones.
E) natural selection.

Historically, most evidence for homology and the common ancestor was based on ________.
*A) comparative anatomy.
B) cytochrome c.
C) convergent evolution.
D) RNA base sequence.
E) polygenic inheritance.

Questions used in 2002 relating to this outline (and other outlines)

In a population of wild flower, there is this frequency of flower color alleles: R (red, dominant) = 0.8, r (white, recessive) = 0.2. Which describes how the r allele might be eliminated if only a few individuals from each generation reproduce?
(a) the Hardy-Weinberg theorem
(b) punctuated equilibrium
(c) sympatric speciation
(d) altruism
*(e) genetic drift

The term "allopatric" was used in the context of
(a) whether symbiosis benefits both parties.
*(b) the formation of new species when the parent population becomes geographically isolated.
(c) whether the organism provides its own nutrition or needs to feed on others.
(d) whether the organism requires O2.
(e) whether evolution was gradual or sudden.

When structures in two different species are evolved from a common ancestor, this is an example of
*(a) homology.
(b) coevolution.
(c) convergent evolution.
(d) sexual selection.
(e) altruism.

Suppose that the red flower allele is dominant to the white flower allele and that the frequency of the red allele in the population is 0.8 while the frequency of the white flower allele is 0.2. What proportion of plants will have red flowers?
(a) 0.2
(b) 0.5
(c) 0.64
(d) 0.8
*(e) 0.96

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