Evolutionary Genetics Theory of Genetics – Blending Inheritance – Lamarckian – Pangenesis • Mendel Studied Peas

11/3/2012

Darwin and Genetics

• Darwin studied snapdragons – Came up with a incoherent Evolutionary Genetics theory of genetics – Blending inheritance – Lamarckian – Pangenesis • Mendel studied peas

Gregor Mendel Genetics Review

• Austrian monk • Gene • Did experiments from 1856 – 1863 • Locus • Published his finding in obscure journal • Allele • Mendel’s laws rediscovered in 1900 • Genotype – Mendel given credit • Phenotype • Rise of biometricians • Homozygous – Focus on variation • Heterozygous – Downplayed Mendel • Dominant • Reconciliation during the Modern Synthesis • Recessive – Polygenic inheritance

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Mendel’s Laws Mendel’s importance to evolution

• Law of Segregation • Particulate inheritance – For each trait there is a gene with two copies – Collapse of blending (alleles) – Blending would make natural selection untenable – Alleles separate during gamete production • Law of Independent Assortment – Loci are independent – Doesn’t work if genes are linked

DNA DNA vs. RNA

• Polymer of nucleotides • DNA • Deoxyribose, base, phosphate group – double helix • Pyrimidines (cytosine [C], and thymine [T]) – Relatively stable • Purines (adenine [A], guanine [T]) • RNA – • Antiparallel strands held together by H bonds Single strand – Unstable • A –T (two H bonds), C – G (three H bonds) • Few RNA-based lifeforms

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DNA to Proteins DNA to Proteins

• Portion of DNA unzips • mRNA contains sequences that are removed – An RNA transcript is produced – Intervening sequences (introns) – Complementary base pairing except uracil (U) for – Exons remain and are spliced together T – Exon splicing can be variable – Messenger RNA (mRNA) – Ribosomal RNA (rRNA) – Transfer RNA (tRNA) – microRNA

mRNA to Protein Genetic variability

• Codons • Crossing over • 3rd position wobble – Creates new combinations of alleles at different loci

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Mutations Mutations • Silent or synonymous mutations • Ultimate source of variability • Missense mutations • Nonsense • Base substitution – Transitions • One purine to another • One pyrimidine to another – Transversions • Purine to a pyrimidine • Pyrimidine to purine

Mutations: Insertions, Deletions, Gene Duplications

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Human-chimpanzee

MPE 2009. A molecular phylogenetic survey of caprimulgiform nightbirds illustrates the utility of non-coding sequences.

Fig. 4. Best estimate phylogeny based on Aneuploidy combined analysis of cytochrome b and c-myc. Topology is the majority rule consensus tree from the combined ML • The result of nondisjunction bootstrap analyses (i.e., nodes with support below 50% are collapsed). Numbers above branches are ML bootstrap values

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Polyploidy

A triploid cytotype of Echinodorus tennellus. Aquatic Botany 2004.

Mutations are random Mutations and fitness

• Mutations are random! • Generally classified as • Mutations are random! – Beneficial • Mutations are random! – Neutral – Deleterious • However fitness is a continuous trait • The frequency of each type of mutation depends on the context

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Mutation and Fitness

• The frequency of each type of mutation depends on the context • In general, most are deleterious or neutral • In stable environment, beneficial mutations are rarer • In changing environment, greater probability of having beneficial mutations – Could be the same mutation that would be deleterious in a stable environment!!!