BIO 370 Lecture Notes - Lecture 3: Blending Inheritance, Mendelian Inheritance, Start Codon
Lecture 3:
Early formal ideas on inheritance:
• Work of Joseph Kolreuter, supported theory of blending inheritance.
• First experimental study of inheritance.
• Bred tobacco plants, found offspring usually intermediate b/w parents.
Blending inheritance: factors dictating heredity are blended together from one generation to the
next. Both parents make equal contribution to offsprings’ traits.
• Evolution made people think blended traits could change over generations typically
through acquired inheritance (Lamarckian).
o Problem for variationists** because not all traits will be shown?
• Reduces diversity, can’t explain re-emergence of traits, there was no good alternative to
this theory.
Mendel’s laws: focused on traits for preliminary experiments seemed to show were inherited
independently of one another.
• Creating a pure-bred lineage: crossed 2 true-breeding homozygotes (F1), gets self
fertilized to create F2 generation (3/4 1st parent, ¼ 2nd parent). Factors were inherited
randomly from each parent, meaning that one had to segregate independently from the
other.
• Akam’s razor: simplest explanation is the best = Mendel used this rule, determined there
were only two factors that determined this instead of 4. Factors randomly segregated.
o Re-emergence of traits proved blending inheritance wrong, which would’ve not
explained how lost traits later re-emerged.
• Law of independent assortment: allele passed down to next generation at 1 locus is
independent of which allele is passed down to the next generation at another locus.
o Applies for genes on different chromosomes (unlinked loci), NOT for linked loci.
• Mendel: hereditary determinants of phenotype were particulate, may blend but they
themselves remain distinct, can be separated again in future reproduction.
DNA: changes in DNA sequences and how those are expressed underlie process of evolution.
• Nucleotides: pair bonding b/w bases is due to non-covalent H-bonds.
o Purines: 2 rings, adenine, guanine.
o Pyrimidines: 1 ring, thymine, cytosine.
• Prokaryotic chromosome structure: round, repetitive sequence.
• Eukaryotic chromosome: composed of 2 chromatids, each end has 5’ end with terminal
phosphate group and 3’ end with terminal hydroxyl group.
• Transcription: DNA double strand unzips, unwound, copied in RNA (complimentary +
antiparallel fashion) after RNA polymerase binds promoter to begin transcription.
• Splicing: removing introns.
• Translation: RNA made can become rRNA (protein production), tRNA (transport amino
acids to ribosomes), miRNA (gene regulation), or mRNA (specifies which amino acid to
link together and make protein)
o Ribosome attaches mRNA, moves in 3’ direction, reaches start codon, pairs
appropriate tRNA with the next codon each linked by peptidyl transferase.
• Post-translational modifications.
• Genetic code is redundant.
• Loci: position of a gene.
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Document Summary
Early formal ideas on inheritance: work of joseph kolreuter, supported theory of blending inheritance, first experimental study of inheritance, bred tobacco plants, found offspring usually intermediate b/w parents. Blending inheritance: factors dictating heredity are blended together from one generation to the next. Random mutations more likely to be deleterious, but important because variation. Undirected, random, shows that evolution is not progressive, as opposed to acquired inheritance: effects on fitness: most mutations are either neutral or deleterious. Bimodal distribution: higher level changes: chromosomal rearrangements (deletion, multiplication, merging, splitting) creates heritable changes in prokaryotic genome and shuffles further in eukaryotic genomes, transition mutation: purine purine, pyrimidine pyrimidine. Maintain spacing, regardless of mismatched h-bonds: transversion mutation: purine pyrimidine, pyrimidine purine. Occurs more than transition because they"re typically repaired. Distorts helix, but easier for repairs: synonymous (silent) mutation: base change that doesn"t alter amino acid of codon. More likely to get if base change in 3rd position of codon.
