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HMB265H1 (200)
Lecture

Notes taken during lecture


Department
Human Biology
Course Code
HMB265H1
Professor
Stephen Wright

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MIDTERM two weeks from today Calculators ALLOWED
Sample midterm will be posted same format as actual midterm
Do studying then practise with midterm questions
Use old exams to practise AFTER STUDIED
50 minutes so careful timing
Additional practise questions will be posted
COVERS EVERYTHING UP TO LEC11 (Tuesday before the exam)
oTuesday lecture will be half new content, and half review
Experimental evidence form Morgans lab genes located on chromosomes
Unusual progeny
oWhite eyed females and red eyed males
oLinking microscope observations with the progeny
Chromosomes separate under microsope
oChromosomal evidence that genes located on chromosomes
Sex determination in Drosophila
Based on how many copies of autosomes relative to sex chromosomes
o1 X and 2 autosomes maleness
o2 X and 2 autosomes femaleness
X chromosome making protein; autosomes make blue protein
oThese proteins dimerize
oExcess of red proteins red dimerize with each other, fruit fly is thus
female
oMales do not have excess of red
Different types if nondisjunction events
oBtw humans and Drosophila
Turtles sex determined by environment
Y chromosome in males why is it that Y and no X dies?
Essential genes on X chromosome absent from Y chromosome
Y chromosome is a degenerate version of X chromosome
oOriginally, very similar, but Y chromosome degenerated and lost several
essential genes
Y chromosomes have genes specific to male phenotype, fertility
Crucial validation of chromosome theory
Dosophila and other animals instrumental because of presence of distinct sex
chromosomes, despite being homologous
oSo crucial physical demonstration that genes located on chromosomes
Gene controlled red v. white eyes found on X chromosomes
Can now visualize genes and locate them on chromosomes
- geneticists inferred from crosses and linking up phenotypes without today’s
technology
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TODAYS LECTURE
Extend on last lecture
LINKAGE AND RECOMBINATION
Experiments that demonstrated we have partial linkage
Morgans lab found many phenotypic mutants
Suttons hypothesis
Eye colour and sex cosegregate for instance
But this may be an unusual case, an exception
Two X-linked traits
Found other traits linked to X chromosome
oFor instance, body colour
oInbred lines of female
+ means wild type, and is dominant over the absence of +
***
Mother will pass on wy+ to progeny
Father will pass on w+y to daughters; Y to sons
Yellow is recessive, red is dominant
F1
oFemales will have both dominant phenotypes
oMales will have white eyes
F2 - ???
oIF assuming Independent Assortment, mother will have four different
gametes appearing at equal frequencies ***
oUnder linked assortment, wy+ passed onto daughter, so maybe its a
single unit
oW+y from dad
Assuming linked, then mother will make only wy+ and w+y
So wouldnt see recombinant types under this assumption
oMorgans lab results in the male progeny
Wy+ and w+y saw in greater numbers than wy and w+y+
Parental types in much higher abundance than the
recombinant types the mother didnt get from her mother
Not seeing independent assortment
oNot seeing 1:1:1:1
EXPLAIN
Parental alleles are linked and so co-assorting, except for occasional split-up
OR
o Something unique to these three traits of sex, eye colour and body colour
Whatever the parents genotype, the progeny showed in much greater numbers
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