Tetrad analysis

אסקוס

/ מיוזה/ תוצר נבג טטרדהספורה

Replica plating

Replica plating

YePD

-ADE

-URA

-TRP

-LYS

URA3 TRP1 ade2 lys2

URA3 trp1 ade2 lys2

ab X a+b+

A

a

B

b

PD

A

a

A

a

B

b

B

b

A

a

A

a

b

B

b

B

NPD=

A B

a b

A B

a b

A B

a bA B

a b PD only

A B

a b

X

A B

a b

A b

a B

TT

Thus RF=1/2TT

הכפולות הרקומבינציות עם מה ?אבל

מכך ויתרה כפולות רקומבינציות כולל אינו הקודם החישוב כלומרה כי מטעה כפולות TTהוא גם ....כולל

Assuming that, in our hypothetical cross of a+ b+ × a b, the observed frequencies of the ascus classes are 56 percent PD, 41 percent T, and 3 percent NPD. Using the formula, we find the map distance between the a and b loci to be:

Let us compare this value with that obtained directly from the RF. Recall that the formula is:

In our example,

This RF value is 6 m.u. less than the estimate we obtained by using the map-distance formula because we could not correct for double crossovers in the RF analysis.

SummaryPD=NPD - No linkage

PD only high linkage maybe the same gene

PD>TT>NPD -Linkage

RF=1/2(TT+6NPD)

Repair, and Recombination

• E. Coli SOS system

Emergency response that allow the insertion of non specific base!

In bacteria its DinB, UmuC and UmuD that encode for pol IV and V, the error prone polymerase that incorporate an arbitrary base across to the damaged base.

Pol eta/iota

Direct reversal By photolyase

Base excision repair

• Start with glycosylase that break the sugar-base bond* and release the altred base and generating apurinic or apyrimidinic sites.

* For example guanine +EMS -> 0-6-ethylgunine (can mispaired with Thymine)

Nucleotide excision repair (NER) in bacteria

Nucleotide excision repair (NER) in yeast

XPD and XPB – helicaseXPG and XPF - endonuclase

Cockayne syndrome

• Mutation in CSA or CSB causes to retinal degeneration, hearing impairment, ataxia and photosensitivity

• Die very young

Tricothiodystrophy (TTD)

• Mutations in XPD

WT

TTD

Human shows photosensetivity, brittle hair, skin defects and short life span.

XPD -/- mice show also wasting, scoliosis, osteophoresis and melanocyte loss.

WT TTD

3m

15m

Mismatch repair in bacteria

Mismatch repair (NER) in human

Spo11

A

A

A

A

a

a

a

a

A

A

A

A

A

A

a

a

A

A

a

a

a

a

a

a

A

A

A

A

A

a

a

a

A

A

A

a

a

a

a

a

Aberrant ratio

4:4 6:2 2:6 5:3 3:5

Gene conversion