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1MO3_Chapter 14.docx

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Jon Stone

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Human Genetic Variation
Human Variation
Humans vary in many different ways
Physical appearance (skin color, height)
Skills, preferences
Variation in human disease
Humans Variation vs Plant Variation
It is very helpful to control parent mating and to separate groups of offspring and grow them in known conditions.
In short-lived, model organisms, we can start with lines that are homozygous (also called pure-breeding or true-breeding). With peas,
Mendel could self them for generations to ensure they were true breeding. Can’t do this with humans.
Variation in Traits Influenced by Single Genes
Genetic variation
o Ex: Sickle-cell anemia
Specific Language Impairment (SLI)
o Runs in families
o Pattern of inheritance consistent with dominant allele at single locus
FOXP2 gene
Causes of Genetic Variation within Groups
Selectionmutation balance
o If gene freq. of PKU allele is 0.001, freq. of babies with PKU is 0.000001
Balanced polymorphism
o Heterozygous individuals have highest fitness
Variation in Complex Phenotypic Traits
Many traits influenced by many different genes
o Ex: Bell-curve distribution
o Heritability
o Environment affect covariation
Variation in Complex Phenotypic Traits
Twin studies
o Monozygotic
o Dizygotic
Genetic traits should be more similar in monozygotic twins than dizygotic
Causes of Genetic Variation among Groups
Natural selection in different environments
o Sickle-cell anemia
o High frequency for “S” allele in regions with malaria
o Higher fitness in S allele carriers with malaria
Genetic drift and founder effects
Culture creates natural selection
Lactose tolerance
o Northern Europe and northern Africa
o ingle, dominant gene
Two mutations in different populations
Genetic Mismatches for Current Environment- Speculation
o Genetic basis
o Insulin regulates uptake of sugar in cells
o NIDD would have helped build fat reserves during times of plenty
Genetic Variation: Lactose Tolerance
Lactase persistence
~6,000 years ago
o Bones of cattle
o Pottery with milk residues
o Early weaning of calves from isotopes
o Lactase persistent allele not present yet
Detecting Selection in the Genome
Selective sweeps
o Crossing over means large sections of DNA carried together with selected allele
o Haplotypes
o SNPs
Genetic Variation among Groups: Height
Variation in height
o Natural selection
o Body size increases in cold climates
o Environmental factors
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