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ch7-part2 - Chapter 7 mitotic crossing-over/recombination...

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Chapter 7 mitotic crossing-over/recombination – produces progeny cell with a combo of genes which differs from that of the diploid parental cell that entered the mitotic cycle; non-inheritable o occurs at a stage similar to the 4-stranded prophase I forms rarely, so this event is rare o Curt Stern – 1936 – Drosophila X-linked genes twin spots – a mosaic phenotype spot w/in mostly wild type phenotype b/c twin spots adjacent, they must be reciprocal products of the same event F1 genotype – sn y+/sn+ y genes in repulsion o then, mitotic X-over – occurs after gene duplication twin spots when X-over w/ both chrom on one side single recessive spot when X-over btwn gene loci o other recessive spot occurs w/ a Double X-over o in general, mitotic X-over makes all genes distal to X-over (btwn X- over pt and end of chrom arm) homozygous IF chromatid pairs align appropriately at the metaphase plate (happens ½ of time – if each arm that underwent X-over pairs w/ arm that didn’t undergo X-over) o In Aspergillus nidulans (fungus) can be used to construct genetic maps can’t do meiotic X-over b/c organism selfs suitable for mitotic recomb studies asexual spores are uninucleate phenotype of each asexual spore controlled by genotype can fuse 2 haploid strains that differ in nuclear genotypes by mixing them together o called heterokaryons – 2 nuclear types coexist in same mycelium and divide mitotically w/in the same cytoplasm Strain 1: w ad+ pro paba+ y+ bi Strain 2: w+ ad pro+ paba y bi+ white –w-> yellow –y-> green heterokaryon is mottled yellow & white spores haploid nuclei in heterokaryon rarely diploidize
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