Variation
Betsy Beeson
Amy Ledebuhr
Definitions/ Review
 Variation: The processes of mutation and recombination that give rise to many
characteristics among the members of a population or species.
 Phenotype: characteristic in a individual organism or group that you can
physically see.
 Genotype: the genetic constitution of an individual organism or a group of
organism that is alike at one or more loci.
 Locus: a site on a chromosome that a gene occupies.
 Allele: a form of a gene distinguished from other alleles by its effects on the
phenotype.
 Haplotype: one of the sequences of a gen or DNA segment
Types of Variation
 Genetic Variation
o Three types
 Mutations
 Change in DNA, single mutation can cause huge
differences
 Gene Flow
 The movement of a gene from one population to another.
 Sex
 Introduce new gene combinations into a population
o These are present at birth
o Color differences caused from alleles
 See page 190 and 191 of our test Snow goose and African swallow
tail
~ Can you think of any other species that show genetic variation?

Environmental Variation/ Maternal Effects
o Maternal Effects- refers to the effects the mother has on her offspring but
are not inherited from her
 Amount of composition of yolk in egg
 Maternal care she provides
 Physiological conditions while caring eggs
o Color change due to the environment the species lives in.
 See page 190 of text figure 9.1 (B) Willow ptarmigan
~ Other species that show environmental variation?
Hardy-Weinberg
 Says that the alleles for a given species next generation are chosen randomly and
independently of each other.
 Assumptions of the Hardy-Weinberg Principle
o Mating is random
o The population is infinitely large
o Genes are not added from outside population
o Genes do not mutate from one allelic state to another
o All individuals have equal probabilities of survival and reproduction
 Two alleles A and a with two frequency p and q
Punnett square for Hardy–Weinberg
equilibrium
Females
A (p)
a (q)
A (p)
AA (p²)
Aa (pq)
a (q)
Aa (pq)
aa (q²)
Males

Three possible genotypic types can result
o F(AA)=P2
o F(Aa)= 2pq
o F(aa)=q2

Assumptions of the Hardy-Weinberg Principle
o Mating is random
o The population is infinitely large
o Genes are not added from outside population
o Genes do not mutate from one allelic state to another
o All individuals have equal probabilities of survival and reproduction
Inbreeding / no variation
 Is the mating of closely related individuals and results in inbreeding depression;
the decline in components of fitness, survival and fecundity of a population.
 This is a larger problem in smaller populations and zoo’s
o The adder snake from Sweden
 With no help
 Fewer the 40 individuals
 Highly homozygous
 Females had small litter sizes
 Offspring were deformed or stillborn
 20 new males introduced for 4 mating season and removed
 The population increased dramatically
 Survival increased
o Inbreeding Testing on Lab mice
 None have as long of a life span as out-bred mice
 Typically become extinct after 5 to 10 generations
 Health problems
 Tumors in 29% males and 55% females
 Small kidneys
 Low weights
 Extra feet or toe bones
Geographic Variation
 Patterns:
o Sympatric: populations that have overlapping geographic distributions
such that they occupy the same area and can frequently encounter each
other
o Parapatric: Populations with adjacent but non-overlapping geographic
ranges that come into contact.
o Allopatric: populations with separated distributions
~Examples of species





Example: Darwin had the idea of species variation when he was on the Beagle in
1831. He was told that it was possible to determine which island a given species
of giant tortoise came from by the shape of its shell. He then began focusing on
the island’s birds (The Galapagos finches)
*All finches or all different species?
Example: Alfred Wallace printed a paper in 1864 taking note on the geological
variation of Malayan butterflies. He noted that local varieties were often found on
islands and pointed out the impossibility of drawing a sharp line between varieties
(which pattern is this??)
Adaptive Geographic Variation
 Bergmann’s Rule: positive relationship between body size and latitude.
 Allen’s Rule: populations of birds and mammals in colder climates tend to have
shorter appendages
 Gloger’s Rule: animal populations in more arid environments are paler in color.
o Example: the author of Darwinian Dynamics basically explains how after a
species migrates to an area, only the fittest survive because the organisms with
the “lower quality” genes die off. (Michod, 2007)
~Examples of these?



Geographic variation among humans
 Linnaeus had a few basic races. Caucasian was at the top followed by Mongolian,
American, Malay, and Ethiopian and each was more degenerative than the last as
a justification for their exploitation of Africans as slaves.
 “Homo sapiens is a single biological species. There exist no biological barriers to
interbreeding among human populations, and even the cultural barriers that do
exist often break down” (Futuyma, 2005).
o -Physical characteristics: skin color, hair texture, shape of incisors, and
stature have been used by various authors to define anywhere from 3 to
more than 60 “races.”
Back to the debate…
 Among Africans, Congo pygmies are the shortest of humans, and Masai are
among the tallest.
 What do you call these then? Species? Sub species? Races?
Reference
Bowler, Peter J. Evolution: the History of an Idea. 3rd ed. London: University of
California P, 2003.
Futuyma, Douglas J. Evolution. Sunderland: Sinauer Associates, 2005. 189-224.
Hamilton, W.D. 1996. Narrow Roads of Gene Land. Freeman and Sons
Michod, Richard E. 1999. Darwinian Dynamics: Evolutionary Transitions in Fitness and
Individuality. Princeton.