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Dividing & DeducingTaking care of genetic information; figuring it out from a standing start
How? Why?
Lab 8
5
Why Mendel Matters
The laws governing inheritance are for the most part unknown; no one can say why the same peculiarity in different individuals of the same species, or in different species, is sometimes inherited and sometimes not so; why the child often reverts in certain characteristics to its grandfather or grandmother or more remote ancestor; why a peculiarity is often transmitted from one sex to both sexes, or to one sex alone, more commonly but not exclusively to the like sex.”
--Charles Darwin, The Origin of Species
…Because Darwin sucked
7
Today...• We will figure out the dominant trait and
genotype for a set of individuals• There will be no luck, no guessing, no
random stabbing in the dark involved• We will generate and explore all possible
(simple) hypotheses and rule out those that do not fit, until only one viable one remains
Meiosis & PhenotypeToday we’ll:
• Refine problem-solving skills• Explore all strategies & outcomes to
determine the best one– And save hours on homework
Thinking it Through• Develop lines of ‘pure breeding’ traits
(green and yellow peas)• Cross them… ONLY yellow trait is
evident– TWO hypotheses?– One test?
Answer1) the green trait had been
destroyed, pushed out, eliminated
2) the green trait was silenced/hidden/overwhelmed
12
Holmes had it rightWhen you have ruled out the impossible, that which remains, however improbable, must be the truth.
--Sir Arthur Conan Doyle
Basic principle of science--we work by listing hypotheses & trying to kill as many as possibleIf one survives, it’s our best description of the universe--provisionally
13
Scaling
•A gene is ~1,000-100,000 basepairs*
•A chromosome is tens or hundreds of thousands of genes
*Includes control regions & stuff that won’t make it into the final product
14
Blinding you with Science (jargon)
• Gene: A stretch of DNA that represents all the information for a product as well as when and where to make the product
• Allele: A version (or flavor) of a gene; two alleles of the same gene my differ by a nucleotide or dozens of them--generally a small number
• Dominant/recessive: Two alleles enter; one allele leaves (which version manifests in the organism)
– NOT which version is more common!
15
The Bigger Picture• Which traits are dominant? What are individual
genotypes? You can use sex to find out!
• Today we’ll engage in some specific problem-solving techniques
– Combinatorial thinking
– Enumerating hypotheses
– ‘Last one standing’
– Orderly approaches & record keeping
Bang it out• You don’t know, but you can “*make sex” to
figure it out!
* that’s about as romantic as I get
17
Blinding you with Science (symbols)
• Allele: A version (or flavor) of a gene; two alleles of the same gene my differ by a nucleotide or dozens of them
– Common symbolism: A vs. a or BLU vs. blu (etc.)
• Homozygous: ‘same-pairing’ = has identical alleles (AA, aa)
• Heterozygous: ‘different-pairing’ = has different alleles (Aa)
19
Puzzle: What’s dominant?• Imagine you are confronted with
two phenotypes (foot color)• Can you tell which is dominant• What crosses should you do to
quickly assign dominance & genotype?
• (FYI: these are actually two different species)
Blue: http://theadventuretravelcompany.files.wordpress.com/2009/02/blue-footed-booby2.jpgRed: http://farm3.static.flickr.com/2177/1621918794_be3a25433b.jpg
How will you know what’s dominant?
• Two hypotheses? Blue is dominant vs red is dominant
• First: Blue Dom – which genos => dominant appearance
• Recessive phenotype• All possible blue x blue in Blue world?• All possible red x red in Blue world?
How will you know what’s dominant?
• Two hypotheses? Blue is dominant vs Green is dominant
• First: Blue Dom – which genos => dominant appearance
• Recessive phenotype• All possible blue x blue in Blue world?• All possible green x green in Blue world?
What crosses yield all blue?All red?
Whatcha got?• Which models can explain all green
offspring?• Anything useful?• How useful to cross to ‘same’
organisms?– ‘need’ heterozygotes– How do you get them if you don’t know?
A better way?• Need more room? Open x_plorer• Graded exercise – show me ‘Total
Victory’ and explain what/why you won (100% or 0%)
MORE Vocab• Naming is hard. Your parents are their parents’
children. So what’s a parent & what’s a child?• In x_plorer: parents stay parents• Formally, you will hear P1, F1, F2 in crosses• P1: the initial parents for the events in question• F1: First filial (of pertaining to, or benefiting a son
or daughter)• F2: Second filial
x_Plorer• An exercise to guide you in thinking• Simultaneously consider two alternative
hypotheses about dominance (left half; right half)
• Work through BOTH cases until you have an ordered set of tests (algorithm) to distinguish (i.e. rule one OUT)
• Watch the lavender box for ‘what to do next’
31
Believing what you read“The genetics of dimples is actually rather interesting. Dimples are a dominant trait, which means that it only takes one gene to inherit dimples. If neither of your parents has dimples, you shouldn't have them either, unless you experience a spontaneous mutation. If one of your parents has dimples, you have a 25-50% chance of inheriting the gene, since it means that parent inherited the gene from one or both parents. If both of your parents have dimples, you have a 50-100% chance of inheriting the gene, depending on how they inherited their dimple genes.”
http://www.wisegeek.com/what-are-dimples.htm
On desktops, with chalk!
MendelStar!• Given the outcome, can you predict the
genotype of the parents?• Observe, Hypothesize, Predict,
Model/Test• Have a plan• Write it down
MendelStar!• For practice purposes, use the ‘Just Mendel’ option• If NOT logged in, tutorial in main lab walks you
through ‘mating and sorting’ (Show Me... menu)• If all that color & such is bugging you, use the
‘Image Simplify’ menu to focus on 1 trait• When not logged in, go to the ‘Evaluate’ destination
for a list of the genotypes in play
Mate your own Butterflies!• Once logged in, choose ‘Find the Genotype’• Work through problems – Have a plan– Write it down! (IF this is TRUE…)– Saves time!
• After answering, hit submit; if score < 76 you’ll get a hint
• You can store at any time by submitting