Goals! Understand what is meant by sex linked genes Understand why red/green colorblindness is more common in males Learn the usefulness of pedigrees!
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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)
Transcript
Quiz #8Given: 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• Autosome: one of the chromosomes that is not an X or a Y• Sex chromosome X or Y (named b/c of where each is joined
together during meiosis)• Symbolism--normally, we don’t care what chromosome a
given allele is on; in sex, it matters• 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• Consider two alleles, A and a
• How many genotypes are there for females? males?
• How many possible crosses are there (by genotype)?
• Each group Punnett one up• recall, XA, Xa, Y
• Also consider the case of the corresponding non-sex-linked cross
• 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”
QuickTime™ and aNone decompressorare needed to see this picture.
Thinking it through• Shown are the only the positions with a
different amino acid between red and green opsins
• How similar do you think their DNA sequences are?
• Remind me--what happens in meiosis when the maternal and paternal chromosomes pair?
• Think anything might ever go wrong?
Launch Opsinze• You’re starting with a ‘red-tuned’ opsin (559nm)
• Your target: as close to a ‘green-tuned’ as possible (531nm)
• Your tool: mutating codon sequences
• From each menu, you can mutate the codon. Identify the AA the codons code for.
• You’ll be shown current and new amino acids.
• After choosing an AA, new absorbance will be displayed.
Male colorblindness• Why are men disproportionally affected by red-green
colorblindness?
Short end of the stick
Now - turn on your hotplates!
Family secretsKnowing your parents by knowing yourself
PTC and parentage• WASH HANDS
• Who can taste this?
• Separate into haves, have-nots
• Each: if trait is dominant, what can you deduce about your parents?
• If trait is recessive?
19Boys & Girls
Chalking up a familyPair up, decide who’s the adult consenting male & who the similarly conscientious femaleYou’re both heterozygotes (recall: ‘different-pairing’)Make the babies--hold an allele in each hand, partner picksHow to determine the sex of the baby?
HOMEWORK!!!!Pediducer
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• Phase I: Assign genotypes; justify
• Phase II: Rule model ‘viable’ or ‘out’• How many contradictions does it take
to rule out a model?
• How many non-contradictions required to justify ‘viable as far as I can tell?’
• “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!• Appendix C--the supplies are on your benches
• Do the Benedict’s test on C-1 (substituting 0.1% glucose for the 1% starch indicated)
