Lab 7: Mitosis and Meiosis

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

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 DNA

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

• Headline: Blue eyes result of ancient genetic ‘mutation’

– It’s not a ‘mutation’; it’s a mutation

Meaning?

A Couple Things to Think About…

https://eapbiofield.wikispaces.com/file/view/12_05CellCycle-L.jpg

It’s all in a name• 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

This

Is just a copy of this

Chromatids and chromosomes

Unreplicated chromosome Replicated chromosome

Chromatids

From Mother

Chromosome 1

Chrm 2

From Father

Chromosome 1Chrm 2

This is a DIPLOID Nucleus/Cell

Chromosome 1(from mother)

Chromosome 1(from father)

Copied duringInterphase

Copied duringInterphase

So after replication…

So after replication…

Chromosome 1(from mother)

Chromosome 1(from father)

Condensed versions during mitosis/meiosis

Chrm 2

Chrm 2

This is ALSO a diploidnucleus/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?

12 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

• 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