Fundamentals of Genetics, Evolution, and Development 17: From Mendelian to Functional Genetics

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Fundamentals of Genetics, Evolution, and
Development17 From Mendelian to Functional
Genetics

• Bio 1111
• Christopher T. Cole
• University of Minnesota, Morris

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7 From Mendelian to Functional Genetics

• Reading
• Recommended Life
• 8th ed
• Ch. 12 section 12.1
• Ch. 13 section 13.4 pp. 296-297

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Genetics, contd.

• Test crosses
• 2 loci
• Mapping
• Complementation analysis
• Gene functions the Operon model

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Test cross 1 locus
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The other lists alleles that father can
contribute
One margin lists each of the alleles that
mother can contribute
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These two parents would have the same
phenotype but when mated with a homozygous
recessive, the offspring would be different
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This gives us the basis for a TEST CROSS
www.monteweston.com
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Test Cross 2 loci

• A test cross for 2 loci allows testing for
  whether an individual is homozygous or
  heterozygous for both loci at the same time
• It also allows testing for linkage

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Margins of a Punnett square for 2 loci also
lists the alleles that can be contributed by
each parent
The 9331 ratio of offspring occurs when the
loci are unlinked
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Test cross 2 loci

• In corn, two unlinked traits are
• Purple (dominant), yellow seeds
• Smooth (dominant), wrinkled seeds
• You are given a corn cob with purple, smooth
  seeds. How would you set up a test cross for
  these seeds?

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Recombination Mapping

• Key idea
• more recombinant offspring loci farther apart

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What genotypes would you expect? What phenotypes
would you expect?
Biology Dept. Penn State
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What proportions would you expect of each
phenotype?
Biology Dept. Penn State
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Biology Dept. Penn State
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How many would you expect if these loci are very
tightly linked, so they are inherited together?
Biology Dept. Penn State
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How far apart are these loci?
Biology Dept. Penn State
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Complementation AnalysisAlleles or Loci?

• If you have two mutants affecting the same trait
  (e.g. a fly with white eyes and a fly with
  vermillion eyes), how do you know whether this
  comes from
• two different alleles at one locus, or
• two different loci affecting the same trait?

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Complementation eye color
Eyes Red WW, Ww or white ww Eyes Red VV, Vv or
vermilion vv
ww x vv
P1
white eyes
vermillion eyes
?
F1
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Complementation eye color
Eyes Red WW, Ww or white ww Eyes Red VV, Vv or
vermilion vv
ww x vv
P1
white eyes
vermillion eyes
All wild type females!!
F1
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Purves et al. Life 7th ed.
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Complementation from genetics to
metabolism What do genes do?
George Tatum
Edward Beadle
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Neurospora crassa fungus growing on a petri
plate with complete nutrient medium
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One gene, one enzyme
Beadle Tatum concluded that each gene
produces a single enzyme (or other protein)
This is confiirmed by complementation
testing different mutants with the same
phenotype (e.g. inability to grow without
arginine) are crossed if their offspring can
grow then the mutations are at different loci
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One gene, one enzyme
Another very powerful result of this method is
that biologists could unravel metabolic pathways.
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Recall The Central Dogma

• DNA RNA protein

Proteins are the machinery of cells they
provide structure and do work
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Despite 3-D complexity, proteins are
fundamentally 1-D structures polymers of amino
acids that fold into their final, working form
Scientific American
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protein
DNA
RNA
co-linearity of DNA, RNA, and protein
Felsenfeld 1985 Scientific American
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Big Question

• How are genes regulated?
• How are they turned on?
• How are they turned off?
• How does a cell know when to make a protein?

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Big Question

• How are genes regulated?
• This was answered without seeing DNA, or even
  isolating DNA all by genetics (i.e. by crossing
  bacteria with different genetic traits)

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Jacques Monod
Francois Jacob
www.mun.ca
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Map of the lac operon defined by genetic
mapping
Weaver 2005 Molecular Biology 3rd ed. Fig 7.16
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Weaver 2005 Molecular Biology 3rd ed. Fig 7.3
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Nice little animations of lac operon function
bcs.whfreeman.com/mga2e/pages/bcs-main.asp?vs13
2n003i283o
vcell.ndsu.nodak.edu/animations/lacOperon/movie.ht
m
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lac repressor DNA-binding h-t-h
www.ionchannels.org
www.uic.edu