BILD 3 Chapter Notes - Chapter 9: Noncoding Dna, Allele Frequency, Genetic Drift
BILD3 Reading Notes 10/24/18
Chapter 23: The evolution of populations
- The smallest unit of evolution
o Evolution only affects population, not individuals
o Microevolution: change in allele frequencies in population over generations
▪ Natural selection, genetic drift, and gene flow change allele frequencies
▪ Only natural selection consistently improves degree to which organisms are well
suited for life in their environment
- 23.1: genetic variation makes evolution possible
o genetic variation
▪ differences among individuals in the composition of their genes or other DNA
sequences
▪ variation can be continuous or binary. If continuous, usually affected by many genes
▪ genetic variation at the whole-gene level (gene variability) can be quantified as the
average % of loci that are heterozygous
▪ nucleotide variability: genetic variation measured at the molecular level of DNA
• little results in phenotypic variation due to introns and exons, and the
redundancy of codons
▪ some phenotypic variation doesn’t result from genetic differences (nonheritable
variation)
o sources of genetic variation
▪ formation of new alleles: by mutation
• some harmful alleles are recessive and hidden from selection through
generations in heterozygous individuals (heterozygote protection). Maintains
pool of alleles not favored under present conditions, but could be beneficial if
environment changes
• neutral variation: mutations in noncoding DNA regions, or redundancy in genetic
code
• only mutations in gametes can be passed down to offspring
▪ altering gene number or position
• translocation of part of one chromosome to another could link genes
• duplication: meiosis errors
• slippage during DNA replication
• transposable elements
▪ rapid reproduction: can quickly generate genetic variation
▪ sexual reproduction: unique combination of alleles from parents
• shuffles existing alleles to produce individual genotypes
• shuffling occurs through crossing over, independent assortment of
chromosomes, and fertilization
- 23.3: natural selection, genetic drift, and gene flow can alter allele frequencies in a
population
o natural selection