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Lecture 2

HMB265H1 Lecture Notes - Lecture 2: Product Rule, F1 Hybrid, Chromosome


Department
Human Biology
Course Code
HMB265H1
Professor
Stephen Wright
Lecture
2

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Lecture 2
-sliding scale for phenotypes like Down’s syndrome or Phenylkatonuria (PKU) has a strong
genetic basis and not a major role for environment but heart disease etc are in the middle,
there are both genetic and environmental components or even multiple genetic components
due to more than one or two genes other extreme is like scurvy where it is purely
environmental due to lack of vitamin C
-organisms tend to resemble their relatives
-pre-mendelian understanding of genetics individuals with favourable traits chosen for breeding
(ex: cattle and crops)implies basic understanding by our ancestors of variable, heritable traits
-mendel examined traits individually, rather than simply considering whole organism controlled
experiments with careful recording and counting (something Darwin did as well,
numerical)chose a good “model” organism (peas)
-good genetic model organism rapid generation time (so you can look at multiple generations)
easy to grow/breed (ex: elephants aren’t good, fruitflies are)can examine large numbers of
offspring (results of genetics are probalistic, there is not one certain outcome, law of large
numbers) can self-fertilize (for plants, not animals)
-usefulness of self-fertilization quick and easy to make pure-breeding /inbred lines, genetically
homogeneous lines that show the same characteristics, generation after generation pure-
breeding=selfed peas that looked the same after many generations (homozygous for trait of
interest) inbred lines in animals but its more of brother and sister mating than selfing
-cross-and self-fertilization in plants mendel could cross pollinate, take pollen from one flower
and put it to another stigma, important to remove anthers of that target flowers so it didn’t self
fertilize, needed a control cross and can also self, from taking pollen from sane plant and
deposited on the stigma
-another reason why peas are good possess a number of “simple” discrete variable traits that
can be clearly recorded probably Mendel didn’t know at the time though simple inheritance
pattern
-discrete vs continuous traits discrete –simple genetics(single gene traits, ex: either green or
red and no intermediates) continuous-complex inheritance (whole range of phenotypes,
polygenic inheritance and a role for the environment like the sliding scale of diseases)
-7 discrete traits in peas round or wrinkled yellow or green purple or white petals inflated or
pinched ripe rods green or yellow unripe pods axial or terminal flowers long or short stems
-dominance one of the two traits in an antagonist pair was dominant and would always be
manifest in the hybrid first thing Mendel did was take inbred lines, and crossed them to each
other, first thing he found, was in the F1 generation, all plants were one of the two phenotypes
(ex: all purple), uniform in F1, one of the two traits here, consistent for all thes traits showed up
in the F1 generation and other one was gone, trait that showed up=dominance, trait that didn’t
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