Phenotypic variation in the GAB character

A. sexlineata: reproduces sexuallyRecombination of homologous chromosomes

A. tesselata: reproduces parthenogeneticallyRecombination of sister chromosomes

Therefore, source of variation in GAB is notrecombination.

Conchas: GPI variationGPI ac: low countsancestral

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 subspeciesRecognizable subspecies would have to be allopatric.

Colaptes auratus caferColaptes auratus auratus

One problem: discordant character variation

Parapatric distributions withintergradation 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 arequantitative characterscontinuous characterse.g. skin color

Phenotypic expressionin and among populationsgenerally fits a normal distribution

A common “racial” characteristic is skin color.

These groups easy to identify because of non-overlapping variation.

Gaps

685 nm

Skin color in 22 human populationsSamples of malesMean +/- one standard deviation

Clinal variation

• 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 Populationdifferences