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 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

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’Headline –It’s not a ‘mutation’; it’s a mutation Meaning?

A Couple Things to Think About…

It’s all in a name Chromosome Gene Chromatid Allele Homologous Dominant Recessive Spindle Fiber Centromere

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 1 Chrm 2

This is a DIPLOID Nucleus/Cell

Chromosome 1 (from mother) Chromosome 1 (from father) Copied during Interphase Copied during Interphase

So after replication…

Chromosome 1 (from mother) Chromosome 1 (from father) Condensed versions during mitosis/meiosis Chrm 2

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 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