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

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, 2 16 =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 MAT  MATa/MAT  (2n)  synthesis (4n) -> meiotic div. I - > meiotic div. II -> spores: MATa; MAT  MATa; MAT 

Classical genetics Monofactorial cross, ie. A (wt) x a (mut) 2:2 pattern of segregation if 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 is linked to the centromere

Centromer linkage 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