Transcript Lecture 16 (3-4-11)

Phenotypic variation in the GAB character
A. sexlineata: reproduces sexually
Recombination of homologous chromosomes
A. tesselata: reproduces parthenogenetically
Recombination of sister chromosomes
Therefore, source of variation in GAB is not
recombination.
Conchas: GPI variation
GPI ac: low counts
ancestral
GPI ab: high counts
Variation among 18 killifishes for phosphoglucomutase
Alleles
Patterns of Geographic Variation
• Arrangement of phenotypic variation in natural
populations
• Some populations recognized as subspecies
• A biological race = a subspecies.
• Phenotypically diagnosable populations occupying
allopatric subdivisions of the range of a species.
• Subspecies have accumulated different allelic
variation (via mutation).
• Therefore, they express different fixed
characteristics.
Example of subspecies
Recognizable subspecies would have to be allopatric.
Colaptes auratus auratus
Colaptes auratus cafer
One problem: discordant character variation
Parapatric distributions with
intergradation at
boundaries
• Second problem: subspecies may be nothing more
than slices of clinal variation
• Cline = a character gradient
• E.g. human race concept.
• There is no satisfactory biological definition of a
human race!
• Misconception: there are character states unique to
particular groups of humans
• The characters traditionally used are quantitative
characters with continuous variation.
“Racial” characters are
quantitative characters
continuous characters
e.g. skin color
Phenotypic expression
in and among populations
generally fits a normal
distribution
A common “racial” characteristic is skin color.
These groups easy to identify because of non-overlapping variation.
Gaps
685 nm
Clinal variation
Skin color in 22 human populations
Samples of males
Mean +/- one standard deviation
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There IS geographic structuring of allele frequencies.
Genetic distance map
42 native human populations
Distances based on frequencies of 120 different alleles
Closer proximity in graph = greater genetic similarity
Genetic similarity is related to geographic distances among the groups.
• PPPPPopu
Population
differences