Genetic variation and selection
Genetic variation
Evolution needs genetics
Argument of Darwin and Wallace:
Reproductive ability + environmental restrictions --> struggle
for existence + heritable variations --> natural selection +
environmental changes --> evolution
Time schedule:
In time of Darwin genetics (1859) did not yet exist
Darwin made the right assumption: genetic variation emerges spontaneously and is
undirected
Mendel did his experiments
Mendel’s laws were rediscoverd (1900)
Darwin’s concept of natural selection (1920-1940) was integrated with the modern
idea of genetics
Terms:
Locus (=gene): position where trait is encoded (considering both
chromosomes)
Allele: one of several varieties of a gene – in diploid organisms every
individual has 2 alleles at a locus
Gene frequency/allele frequency: number of alleles of particular variety in
a population
Homozygote: 2 alleles at a locus in one individual are identical
Heterozygote: 2 alleles at a locus in one individual are different
Codominance: heterozygote with both dominant alleles, so both come into
expression
Polymorphism: occurrence of 2 or more different forms (phenotypes) in a
population of a species
Type of variations:
SNP: mutation with single nucleotide (±1 SNP per 100 bp)
Often used for genome-wide scans (GWAS) of genetic variation
associated with diseases
Most SNPs are neutral but some are medically relevant (e.g. LDL receptor)
o SNP in LDL (low density lipid) receptor. LDL support uptake of
cholesterol. So, mutation (SNP) lead to hypercholesterolemia
VNTRs: variable number of tandem repeats – with this you always have a large
number of heterozygotes
Microsatellite: short core (kern) sequence (STS: short tandem repeat)
Minisatellite: core sequence >100 bp
Usually uncoding
VNTR in a coding region: Polymorphism in D4 dopamine receptor (DRD4)
o Long DRD4 variants are associated with ADHD, inquisitiveness
(nieuwsgierigheid), religious inclination (neiging)
Long variatns of DRD4 have had evolutionary advantage
Null hypothesis for genetic variation:
Genetic variation
Evolution needs genetics
Argument of Darwin and Wallace:
Reproductive ability + environmental restrictions --> struggle
for existence + heritable variations --> natural selection +
environmental changes --> evolution
Time schedule:
In time of Darwin genetics (1859) did not yet exist
Darwin made the right assumption: genetic variation emerges spontaneously and is
undirected
Mendel did his experiments
Mendel’s laws were rediscoverd (1900)
Darwin’s concept of natural selection (1920-1940) was integrated with the modern
idea of genetics
Terms:
Locus (=gene): position where trait is encoded (considering both
chromosomes)
Allele: one of several varieties of a gene – in diploid organisms every
individual has 2 alleles at a locus
Gene frequency/allele frequency: number of alleles of particular variety in
a population
Homozygote: 2 alleles at a locus in one individual are identical
Heterozygote: 2 alleles at a locus in one individual are different
Codominance: heterozygote with both dominant alleles, so both come into
expression
Polymorphism: occurrence of 2 or more different forms (phenotypes) in a
population of a species
Type of variations:
SNP: mutation with single nucleotide (±1 SNP per 100 bp)
Often used for genome-wide scans (GWAS) of genetic variation
associated with diseases
Most SNPs are neutral but some are medically relevant (e.g. LDL receptor)
o SNP in LDL (low density lipid) receptor. LDL support uptake of
cholesterol. So, mutation (SNP) lead to hypercholesterolemia
VNTRs: variable number of tandem repeats – with this you always have a large
number of heterozygotes
Microsatellite: short core (kern) sequence (STS: short tandem repeat)
Minisatellite: core sequence >100 bp
Usually uncoding
VNTR in a coding region: Polymorphism in D4 dopamine receptor (DRD4)
o Long DRD4 variants are associated with ADHD, inquisitiveness
(nieuwsgierigheid), religious inclination (neiging)
Long variatns of DRD4 have had evolutionary advantage
Null hypothesis for genetic variation:
