Lab 7: Mitosis and
Meiosis
Mitosis and Cell Division
Goals:
• 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
I want to build a house
• What information do I need?
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
Mitosis and Cell Division
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!
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?
‘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
Meaning?
• Headline: Blue eyes result of ancient genetic
‘mutation’
– It’s not a ‘mutation’; it’s a mutation
A Couple Things to Think
About…
https://eapbiofield.wikispaces.com/file/view/12_05CellCycle-L.jpg
It’s all in a name
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Chromosome
Gene
Chromatid
Allele
Homologous
Dominant
Recessive
Spindle Fiber
Centromere
Chromatids and chromosomes
Chromatids and chromosomes
Unreplicated chromosome
Chromatids and chromosomes
Unreplicated chromosome
Replicated chromosome
Chromatids and chromosomes
Unreplicated chromosome
Replicated chromosome
This
Is just a copy
of this
Chromatids
From Mother
Chromosome 1
Chrm 2
From Father
Chromosome 1
Chrm 2
This is a DIPLOID
Nucleus/Cell
Chromosome 1
(from mother)
Copied during
Interphase
Chromosome 1
(from father)
Copied during
Interphase
So after replication…
So after replication…
Chromosome 1
(from mother)
Chromosome 1
(from father)
Chrm 2
Chrm 2
Condensed versions during mitosis/meiosis
This is ALSO a diploid
nucleus/cell
This is a DIPLOID
Nucleus/Cell
Mitosis and Cell Division
Why are
chromosomes
usually shown
like this?
Mitosis and Cell Division
• Pick two traits
• Pick a dominant & recessive outcome
arising from different alleles
• You all start off heterozygous
Pay attention to
the ‘nubbins’
Mitosis and Cell Division
• -Take a bead
model
• -What do our bead
models represent?
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
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.
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?
Mitosis and Cell Division
• What comes after MITOSIS?
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?
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
Meiosis
Where should the circled site on
Chromo1 recombine with Chromo2?
1
2
3
Meiosis
• Remember our traits?
• What is dominant/recessive?
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)
Meiosis
• Now we’ve recombined; how to
separate?
• How many resulting cells? Ploidy?
• What else do we need to do?
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?
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
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
Clean Up
No, we’re NOT done
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?
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
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
Gameter
• Explore
– One meiosis
– 200 meioses
– Move ‘em around and try again
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Observe
Hypothesize
Test
Evaluate
See rubric
Disease Presentation
Where we’re headed
• Your proposal is an answerable,
interesting question
• It will reflect causation
• Read my comments, revise proposal
• Turn in next week