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Lecture 5

PSYCH 3GG3 Lecture 5: Lecture 5
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Department
Psychology
Course
PSYCH 3GG3
Professor
Mel Rutherford
Semester
Fall

Description
Lecture 5 – September 15 Darwin's Discovery • Set sail in 1831 - collected many specimens • Published on the origin of species in 1859 • Sold out immediately - widely read and got a lot of attention, internationally known Gregor Mendel • Childhood tasks included gardening and beekeeping • Joined an abbey and became a monk • Discovered particulate inheritance, published in 1866 • Cited 3 times over the next 50 years, no one noticed, did not become known to the scientific community for decades The Modern Synthesis • The modern understanding that Mendel's particulate mechanism of inheritance was the heritable matter than Darwin's theory of natural selection relied upon Darwin's Problem: Blended Inheritance • Understood that offspring inherited something from their parents. But the understanding at the time was that offspring got a blending of the parents • But in this model, new mutations cannot take hold • If there is one tall tree that gets more light and has better fitness, blended selection averages this across the generations and the mutation will never take hold Mendel studied inheritance using pea plants • Look at pea plant with distinct, heritable traits: yellow or green, wrinkled or smooth, tall or short Mendel's critical experiment • Started with two plants that were bred true, tall only from tall and short only from short • In blended inheritance, all plants would be medium, but he got all tall plants in first generation and in second generation, got 3 tall and 1 short plant Mendel's conclusions • Whatever was inherited was particular • Each individual carried two copies of these particulate units of inheritance (gene) • Each parent gives one copy of the "gene" to its offspring • The gene given by one parent does not change the nature of the gene given by the other parent, but it can influence its expression (dominant and recessive) Some terminology Chromosomes - a single molecule comprising a very large DNA helix. A single chromosome may include thousands of genes • Coiled up tight in order to keep the DNA tidy Gene • Defining a gene is much harder to define than a chromosome as is it more of a construct rather than an object Length is not useful in defining what length of DNA is a gene • • Richard Darwin's definition of a gene: "a gene is a portion of chromosomal material that potentially lasts for enough generations to serve as a unit of natural selection " • Definition: a functional sequence of DNA that remains across a large number of generations, potentially for long enough for it to function as a significant unit of natural selection Allele - one possible form of a gene that may occupy a particular locus (location) on the chromosome - only becomes a gene when it is universal to the species • For about 1/3 of loci in humans, there is currently only one viable allele (or gene) - all humans have the same genes at about 1/3 of the loci - universal to the species
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