The mitochondrial genome

• Nucleoid, 75kb, 10 proteins, tRNA, rRNA, „optional“ introns• Relaxed codon usage• Variation in the code, trp, met, thr

Mitochondrial genes

• Mitochondrial function required to grow on non-fermentable carbon sources, lactate, glycerol, ethanol

• Mutations in nuclear genes that affect mito function: PET+ -> pet-

• Mutations in mitochondrial DNA– Wild-type, +

– Large deletions, -

– Loss of mito genome, °

– Single site mutations, , mit- (normal translation)

– Single site mutations, , syn- (deficient in translation)

• Mito mutations give 4:0 segregation

Segregation of mitochondrial

genes

Mitochondrial fusion and fission

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Non-mendelian determinants

• 2 µm plasmid, mitochondrial genes, RNA viruses, • + prions, cytoplasmatic inheritance

, , Sup35p[URE3], [ure3], Ure2p, deficiency in ureidosuccinate

utilization

Advantages of meiosis(sexual reproduction)

• Chromosome mixing, 216=65’536 possibilities• Crossing over -> indefinite number of new

combinations (45x2)• Gene conversion• Gene repair• Generation of new alleles• 2 different isolates of yeast differ every 100bp

meiosis

MATa x MATMATa/MAT(2n)synthesis (4n) -> meiotic div. I -> meiotic div. II -> spores: MATa; MATMATa; MAT

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Classical genetics

• Monofactorial cross, ie.A (wt) x a (mut)

2:2 pattern of segregationif 4:0 -> mito

• Complementation / non-compl. (in Dipl.)• Nonallelic noncomplementation• Allelic noncomplementation• Supression

Bifactorial cross, ie.

AB x ab

If A and B are linked• PD > NPD• The distance of the markers A B determines the number of

PD:NPD:T• cM = (100/2)[(T+6NPD)/(PD+NPD+T)]

• For map distances of up to 4 crossovers (45cM this is ok, >45cM Snow eq.)

• The number of T is proportional to the map distance

If A islinked to the centromere

Centromerlinkage of A

and B

Recombination• General recombination = Homologous recombination• Order of events (I meiotic div):

– 1) Double strand break– 2) Two chromatids from different chromosomes (maternal/paternal) cross over– 3) Base pairing and strand invasion– 4) Synthesis and gap repair– 5) Resolution of Holiday junction

Resolution of Holiday junction

Gene conversion

Geneconversion