Leader: Kirsten Karkow
Course: Biol 211 - Wilsey
Date: 3/25/2012
Worksheet 21
Supplemental Instruction
Iowa State University
Define the following terms.
Homologous Structures – structures that share a common ancestral origin. NOTE: don’t need to
have the same (current) function! Ex. – human arms, whale fins, and bat wings.
Analogous Structures – structures that correspond in function but don’t have the same
evolutionary origin. Ex. – bird wings (reptile origin) and bat wings (mammalian origin).
Vestigial Structures – structures that have been reduced from their ancestral form, and are no
longer functional. Ex. – gills and tails in human fetus, appendix, and manatee nails.
Provide an explanation of how the following support the Theory of Evolution:
1.
2.
3.
4.
5.
6.
7.
Biogeography – continental drift leads to species isolation, affects distribution
Human Selection – breeding leads to huge changes in species (artificial selection)
Fossils – fossil layers give a record of different species at different times
Comparative Anatomy – homologous structures are found in very different animals
Comparative Embryology – closely related organisms develop in a similar fashion
Molecular Biology – DNA is more similar between certain organisms
Convergent Evolution – unrelated species in similar environments evolve similarly
Fill in the blank.
Evolution occurs at the population level. Individuals don’t undergo evolution, they undergo
mutation, which the environment can select for, leading to evolution of the species.
The process by which the environment favors certain characteristics and therefore selects for
certain alleles is known as natural selection. Those organisms that better fit the environment
will exhibit greater survival and reproduction, resulting in more offspring with those “favorable”
adaptations. This leads to changes in gene frequencies (microevolution).
If enough isolation, mutation, and selection occurs in any given gene pool, a new species can be
formed. This is called macroevolution.
Define the following terms.
Gene Pool – the complete collection of all of the alleles of all of the individuals in a population.
Increases when a mutation is generated and survives. Decreases when an allele is lost.
Allele Frequency – a decimal measurement of how often an allele occurs in a gene pool.
Represented by p or q.
Genotypic Frequency – a decimal measurement of how often a genotype occurs in a gene pool.
Calculated as p2, 2pq, and q2 for populations that ARE NOT evolving.
Supplemental Instruction
1060 Hixson-Lied Student Success Center  294-6624  www.si.iastate.edu
Hardy-Weinberg Equilibrium – a principle stating that in a population that isn’t evolving, allelic
and genotypic frequencies will remain constant from generation to generation and will be given
by p + q = 1 and p2 + 2pq + q2 = 1.
Null Hypothesis – assumption that any deviations are due to chance alone (not selection).
Sample Frequency Questions:
The R allele codes for red flowers, while r codes for white flowers. Given that the allelic
frequency of R is .6, find the frequency of r and the genotypic frequencies of RR, Rr, and rr.
Assume the population is in Hardy-Weinburg equilibrium.
Frequency of R = p = .6
Frequnecy of r = q
p + q = 1 → .6 + q = 1 → q = .4
Frequency of RR = p2
Frequency of Rr = 2pq
Frequency of rr = q2
p2 = (.6)2 = .36
2pq = 2(.6)(.4) = .48
q2 = (.4)2 = .16
(.36 + .48 + .16 = 1)
If 98 out of 200 individuals in a population express the recessive phenotype, what percent of
the population would you predict to be heterozygous?
Recessive genotypic frequency = q2 = 98/200 = .49
Recessive allelic frequency = q = √(q2) = √(.49) = .7
Dominant allelic frequency = p = 1 – q = .3
Heterozygote genotypic frequency = 2pq = 2(.7)(.3) = .42
You would expect 42% to be heterozygous
(p + q = 1)
Assuming that the actual frequency of the heterozygote genotype in the above problem is 16%,
what can be concluded?
The population is not in Hardy-Weinburg equilibrium, so the null hypothesis is false.
Evolution is occurring. (There must be selective pressure against heterozygotes.)