Lab 7: Mitosis and Meiosis
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Transcript of Lab 7: Mitosis and Meiosis
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Lab 7: Mitosis and Meiosis
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Mitosis and Cell DivisionGoals:
• Scaling: Nucleotide, Gene, Chromosome--and how many of each
• Differences between mitosis and meiosis
• Predict and describe meiotic results
• Master concepts referred to by: allele, dominant, recessive, linkage
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I want to build a house• What information do I need?
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Scaling• A gene is ~1,000-100,000
basepairs*
• A chromosome is tens or hundreds of thousands of genes
• A genome is 1-100s of chromosomes
• A genotype refers to the alleles present in a given genome
• Human genome is ~3,000,000,000 basepairs
• Human genome is (currently guesstimated at) ~20-30,000 genes**
• Human genome is ~1 meter of DNA
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Mitosis and Cell Division• Gene: Segment of DNA that represents all 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!
• More in the lab manual & Vocab exercises!
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Windows on the gene: eyes• Find a brown- and a blue-eyed person.
Look deep into their eyes & try to figure out the difference
• What does it mean genetically when we say ‘brown eyes are dominant’?
– One gene, two alleles
• Why should that be so? What do brown alleles got that blue do not?
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‘Ripped’ from Headlines• Blue eyes arise from a DNA change that prevents
creation of melanin in the eye specifically
• Mutation appears identical in all blue-eyed folks
• Headline: Blue eyes result of ancient genetic ‘mutation’
– It’s not a ‘mutation’; it’s a mutation
Meaning?
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A Couple Things to Think About…
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https://eapbiofield.wikispaces.com/file/view/12_05CellCycle-L.jpg
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It’s all in a name• Chromosome
• Gene
• Chromatid
• Allele
• Homologous
• Dominant
• Recessive
• Spindle Fiber
• Centromere
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Chromatids and chromosomes
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Chromatids and chromosomes
Unreplicated chromosome
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Chromatids and chromosomes
Unreplicated chromosome Replicated chromosome
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This
Is just a copy of this
Chromatids and chromosomes
Unreplicated chromosome Replicated chromosome
Chromatids
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From Mother
Chromosome 1
Chrm 2
From Father
Chromosome 1Chrm 2
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This is a DIPLOID Nucleus/Cell
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Chromosome 1(from mother)
Chromosome 1(from father)
Copied duringInterphase
Copied duringInterphase
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So after replication…
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So after replication…
Chromosome 1(from mother)
Chromosome 1(from father)
Condensed versions during mitosis/meiosis
Chrm 2
Chrm 2
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This is ALSO a diploidnucleus/cell
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This is a DIPLOID Nucleus/Cell
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Mitosis and Cell Division
Why are chromosomes usually shown like this?
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Mitosis and Cell Division
• Pick two traits
• Pick a dominant & recessive outcome arising from different alleles
• You all start off heterozygous
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Pay attention to the ‘nubbins’
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Mitosis and Cell Division• -Take a bead
model
• -What do our bead models represent?
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Mitosis and Cell Division• SHOW ME
• You can do a lot of fuzzy math (and fuzzy biology and fuzzy chemistry and fuzzy...) up there
• Drawing/speaking/writing forces precision; reveals missing links
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Mitosis and Cell Division• Point at some of your cells that ‘do’
mitosis?
• What’s the goal/purpose of this thing called ‘mitosis’?
• So what must the first step be? Do it.
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Mitosis and Cell Division• Point at some of your cells that ‘do’
mitosis?
• What’s the goal/purpose of this thing called ‘mitosis’?
• So what must the first step be? Do it.
• Now what must be achieved?– Any half? If not, how pick the appropriate
half?
• How do your final results compare with starting?
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Mitosis and Cell Division
• What comes after MITOSIS?
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Meiosis • Why have sex?• How much of your genome do
you want to give your child?• How much are you ‘like’ your
mom and dad?• Do ‘mother’ chromosomes have
to stay together?
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Meiosis – genetic diversity • Just shuffle the chromosomes: all
the genes on every chromosome inherited together
• Recombine between homologs: one set of genes on a chromosome inherited independently of another
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Meiosis Where should the circled site on Chromo1 recombine with Chromo2?
12 3
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Meiosis • Remember our traits?
• What is dominant/recessive?
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Meiosis• First, make a copy--b/c that’s the way it
happens
• Pair the pairs: duplicated mom’s & dad’s contributes pair
• Recombine (randomly)
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Meiosis • Now we’ve recombined; how to
separate?
• How many resulting cells? Ploidy?
• What else do we need to do?
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Meiosis • Now we’ve recombined; how to
separate?
• How many resulting cells? Ploidy?
• What else do we need to do?
• How many resulting cells? What are these cells called?
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Meiosis • Now we’ve recombined; how to
separate?
• How many resulting cells? Ploidy?
• What else do we need to do?
• How many resulting cells? What are these cells called?
• Select a gamete, go fuse with a classmate
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Meiosis • Now we’ve recombined; how to separate?
• How many resulting cells? Ploidy?
• What else do we need to do?
• How many resulting cells? What are these cells called?
• Select a gamete, go fuse with a classmate
• Stop by and show me the genotype
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Clean Up
No, we’re NOT done
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More Vocab…• We’ve talked about chromosomes,
mitosis, and meiosis…
• Recombining genes via Crossing Over
• How likely do you suppose it is that genes are inherited together?
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More Vocab…• Linkage’ - referring to whether
genes are inherited together because they are ‘close’ on a chromosome
• ‘Linked’ - referring to the resulting behavior of traits encoded by such genes
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Gameter • Open Gameter
• Move things around, work with the buttons
• Notice A and a go together
• End up with: ‘A’ and ‘B’ on Chrm II, with A farther right than B
• Ab and AB
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Gameter • Explore
– One meiosis– 200 meioses– Move ‘em around and try again
• Observe • Hypothesize• Test• Evaluate• See rubric
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Disease Presentation
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Where we’re headed• Your proposal is an answerable,
interesting question
• It will reflect causation
• Read my comments, revise proposal
• Turn in next week
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