Transcript pink is dominant

Quiz #8
Given: on a trek in the desert, you come across a population
of prairie dogs. You notice that some prairie dogs are pink
while others are orange. You hypothesize that pink is
dominant.
1. List the genotypes and phenotypes that are possible under
the PINK IS DOMINANT hypothesis. (3)
2. To determine if your hypothesis is correct, what should you
do first? (3)
3. List the possible outcomes of step#1. Which outcome is
helpful to determine dominance? (2)
4. If you are unlucky and get an outcome that was not helpful,
what should you do next and WHY? (2)
Lab #9 - Sex-linkage
and Pedigrees!
Goals!
• Understand what is meant by sex linked
genes
• Understand why red/green
colorblindness is more common in
males
• Learn the usefulness of pedigrees!
Sex chromosomes
• What are they?
• Is the short end the short end of the
stick?
Blinding you with science
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Autosome: one of the chromosomes that is not an X or a Y
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Sex chromosome X or Y (named b/c of where each is joined
together during meiosis)
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Symbolism--normally, we don’t care what chromosome a given
allele is on; in sex, it matters
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•
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On the X, we designate thusly: XA, Xa
On the Y, generally designate: Y
How come no A or a?
Terminology: XA Y is hemizygous--neither homo no hetero, but half
Sexing you up
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Consider two alleles, A and a
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How many genotypes are there for females? males?
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How many possible crosses are there (by genotype)?
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Each group Punnett one up
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recall, XA, Xa, Y
Also consider the case of the corresponding non-sexlinked cross
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What is the equivalent of Y in a ‘regular’
(autosomal) trait?
Can’t tell red from
green?
Human Eye
Rods and cones
A lil deeper...
What our rods and cones “see”
Thinking it through
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Shown are the only the positions with a different
amino acid between red and green opsins
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How similar do you think their DNA sequences
are?
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Remind me--what happens in meiosis when the
maternal and paternal chromosomes pair?
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Think anything might ever go wrong?
QuickTime™ and a
None decompress or
are needed to s ee this pic ture.
Launch Opsinze
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You’re starting with a ‘red-tuned’ opsin (559nm)
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Your target: as close to a ‘green-tuned’ as possible (531nm)
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Your tool: mutating codon sequences
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From each menu, you can mutate the codon. Identify the AA
the codons code for.
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You’ll be shown current and new amino acids.
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After choosing an AA, new absorbance will be displayed.
Male colorblindness
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Why are men disproportionally affected by red-green
colorblindness?
Short end of the stick
Now - turn on your
hotplates!
Family secrets
Knowing your parents by knowing yourself
PTC and parentage
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WASH HANDS
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Who can taste this?
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Separate into haves, have-nots
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Each: if trait is dominant, what can you deduce about your
parents?
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If trait is recessive?
Boys & Girls
19
Chalking up a family
Pair up, decide who’s the adult consenting male & who
the similarly conscientious female
You’re both heterozygotes (recall: ‘different-pairing’)
Make the babies--hold an allele in each hand, partner
picks
How to determine the sex of the baby?
HOMEWORK!!!!Pedid
ucer
Deductions from Pedigrees
A couple rules
• Filled in = they have the genetic disease!
• Outsiders = ALWAYS homozygous
normal
• Can’t tell if hetero or homo dominant?
Use “at least one” dominant option, and
use rational “own phenotype”
Two phases
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Phase I: Assign genotypes; justify
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Phase II: Rule model ‘viable’ or ‘out’
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How many contradictions does it take to rule
out a model?
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How many non-contradictions required to
justify ‘viable as far as I can tell?’
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“No amount of experimentation can prove
me right; a single experiment can prove me
wrong. —Albert Einstein
Out with the old, in
with the new
Say hello to my li’l assay
Two “Tests”
• Benedict’s Test - turns RED when
SUGARS are present
• Barium hydroxide - WHITE precipitate
forms in the presence of carbon dioxide
Do it!
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Appendix C--the supplies are on your benches
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Do the Benedict’s test on C-1 (substituting 0.1% glucose for
the 1% starch indicated)
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Do the CO2 test on C-2
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Check the “Clean-up” tab on website!
Homework
• Pediducer