עצמית מהכלאה רקומבינציה תדירות•'בוחן-'כ Y בכרומוזום שימוש• 2 –עצמית להפרדה תאחיזה בין" הגבול"• mapping" – רואים שלא בשיחלופים התחשבות•

function”

לצנטרומר גן בין ומיפוי, בודדות מיוזות – טטרדות•

נוספות מיפוי שיטות

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The yeast Saccharomyces cerevisiae is commonly used as a model system

==Budding Yeast Budding Yeast =Bakers Yeast=Bakers Yeast

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The yeast Saccharomyces cerevisiae is clearly the most ideal eukaryotic microorganism for biological studies. The "awesome

power of yeast genetics" has become legendary and is the envy of those who work with higher eukaryotes. The completesequence of its genome has proved to be extremely useful as a reference towards the sequences of human and other higher eukaryotic genes. Furthermore, the ease of genetic manipulation of yeast allows its use for conveniently analyzing and functionally dissecting gene products from other eukaryotes.

--Fred Sherman

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Major advantages of the budding yeast as a Major advantages of the budding yeast as a genetic systemgenetic system• Grows fastGrows fast

• CheapCheap

• Compact genome, fully sequenced since Compact genome, fully sequenced since 1996. 1996.

• Easy to handleEasy to handle

• Superb Genetics, Biochemistry, Molecular Superb Genetics, Biochemistry, Molecular BiologyBiology

• Easy to transform, high efficiency of gene Easy to transform, high efficiency of gene targetingtargeting

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Major characteristic of the Major characteristic of the budding yeastbudding yeast

• Unicellular EukaryoteUnicellular Eukaryote

• Grows by buddingGrows by budding

• 16 linear chromosomes 16 linear chromosomes

• Generation Time: ~100 minGeneration Time: ~100 min

• Can exist as stable diploid or haploidCan exist as stable diploid or haploid7

Yeast: A model eukaryote

Yeasts – the ultimate model eukaryote for unicellular issues and some basic cell-cell interactions

Yeast studies have broken new ground in:Cytoskeleton functions transcription mechanisms**cell cycle** transcriptional regulationorganelle biogenesis chromatin modificationsecretion* signal transductionprotein targeting mechanisms protein degradation*chromosome replication DNA repairgenome dynamics retroviral packagingprions recombination mechanismsageing function of new genesmetabolism protein modification

*Lasker Award **Nobel Prize

"for their discoveries of key regulators of the cell cycle"

Lee HartwaellPaul Nurse Tim Hunt

The Nobel Prize in Physiology or Medicine 2001

for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells

James E. Rothman Thomas C. SüdhofRandy W. Schekman

The Nobel Prize in Physiology or Medicine 2013

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What is yeast?

• Yeast - a fungus that divides to yield individual separated cells (as opposed to molds- mycelium)

• Saccharomyces cerevisiae (budding yeast)baker’s yeast closely related to brewer’s yeasts grows on rotting fruits

• Schizosaccharomyces pombe (fission yeast)African brewer’s yeast

• Saccharomyces relatives

(S. bayanus, S. paradoxus, etc.)

• Candida albicans

• Cryptococcus neoformans9

Yeast life cycle

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Yeast cell cycle (mitosis)

•morphology reflects cell cycle position

•same in haploids and diploids

•major control point is ‘start--’

–cells can choose mitosis, meiosis or mating

–depends on ploidy, env. & presence of partner

Morphology + nuclear localization and MT localization indicates the

precise stage of the cell cycle

Major control point is at G1/S

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• Mendel’s rules are relevant for organisms that sexually reproduce: diploid/haploid

–Plants, Animals, many Mora…

Those that ‘do’meiosis

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HaploidMitosis

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DiploidMitosis

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DiploidMitosis

HaploidMitosis

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Of diploid

1n1n

1n

2

1

Of haploid

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Centromere mapping

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Centromere mapping

Nonsister chromatids do not cross over

First-division segregation pattern or MI pattern

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n = 2 -> 4 2 1 1 1 S

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Centromere mapping

Nonsister chromatids do not cross over

First-division segregation pattern or MI pattern

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Centromere mapping

Nonsister chromatids cross over

Second-division segregation pattern or MII pattern

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1. The loci are on separate chromosomes2. The loci are on opposite sides of the centromere on the same chromosome3. The loci are on the same side of the centromere on the same chromosome37

B Mating

Heterozygous diploid

Tetrad

BABAbaba

BaBabAbA

BABababA

NPD PDT TT

Tetrad Dissection

Meiosis

ab A

B a

b A

B a

b A

B a

b A

Unordered tetrads

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Yeast tetrad analysis (classic method)

tetrad

Step1: separate spores by micromanipulation with a glass needle

Step2: place the four spores from each tetrad in a row on an agar plate

Step3: let the spores grow into colonies

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Classical approach (tetrad dissection)

BABAbaba

BaBabAbA

BABababA

NPD PDT TTTetrad

Tetrad Dissection

bni1∆ bnr1∆

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MESSAGE

Linear and unordered tetrads can be used to calculate the frequencies of single and double crossovers, which can be used to calculate

accurate map distances.

Perkin formula

Map distance=50(T+6NPD) m.u42

Meiosis

Mating

Heterozygous diploid

Tetrad

BABAbaba

BaBabAbA

BABababA

NPD PDT TT

Tetrad Dissection

What PD, NPD and T values are expected when dealing with unlinked genes?

BB

aaaa

bb

aaAA

BB

aaaa

aAA

bb

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Meiosis

Mating

Heterozygous diploid

Tetrad

BABAbaba

BaBabAbA

BABababA

NPD PDT TT

Tetrad Dissection

What PD, NPD and T values are expected when dealing with unlinked genes?

BB

aaaa

bb

aaAA

BB

aaaa

aAA

bb

The sizes of the PD and NPD classes will be equal as a resultof independent assortment.

The T class can be produced only form a crossover between the specific loci and the and their respective centromeres

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עצמית מהכלאה רקומבינציה תדירות•'בוחן-'כ Y בכרומוזום שימוש• 2 –עצמית להפרדה תאחיזה בין" הגבול"• mapping" – רואים שלא בשיחלופים התחשבות•

function”

לצנטרומר גן בין ומיפוי, בודדות מיוזות – טטרדות•

נוספות מיפוי שיטות

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Haldane’s mapping function

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The true determinant of RF is the relativesizes of the classes with no crossovers,

versus classes with any nonzeroNumber of cross overs

”mapping function" רואים – שלאהתחשבות בשיחלופים

A formula that relates RF values to “real” physical distance

m-is the mean number of cross overs that occur in a segment per meiosis

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The larger m get e-m tends to 0and RF tends to 1/2 , or 50m.u

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”mapping function" רואים – שלאהתחשבות בשיחלופים

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The inherent tendency of multiple crossovers to lead to an underestimateof map distance can be circumvented by the use of map function

(in any organism ,)and by the Perkin formula( in tetrad-producing organisms such as fungi)

MESSAGE

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