lecture 7
暂无描述。系统推荐的高质量记忆内容，适合每天坚持背诵学习。
卡片预览 (6 张)
If dihybrid cross doesn’t result in 1:1:1:1 ratio what can be inferred? define notations for: known and unknown linkage; known indep assort
• if genes are linked, the parental combination of gametes are overrepresetned • genese close together on the same chr are linked • known linked / • unknown linked . • indep assort ;
Explaing crossing over
• the physical exchange of DNA b/w non-sister chromatids of homologs in prophase 1 • rare occurance • expect that most meiosis to have parental combination of gametes • c/o gives recombinant gametes • freq recomb gametes are proportional to the genetic distance b/w 2 genes
Explain the first proposed model: Holliday Model
• nicking; occuring at the exact same spot on both homologs = dsDNA break • invasion; nicked strand invades the other nicked homolog; must have seq similar to continue • resolution; covalent linkage to form Holliday Junction
How do you know if genes are linked? what are the expected ratios for a test cross and a dihybrid
• over-representation of parental phenotypes in F2 of test cross • progeny doesnt look like 1:1:1:1 • parental alleles were more likely to be inherited tgt than expected from independent assortment • dihybrid cross not expecting 9:3:3:1
How do you measure genetic distance? define RF value
• NOT = to physical distance • recombinantion frequence proportional to the distance b/w linked genes • the further apart 2 loci are, the higher likelihood of a C/O occuring • if 2 loci are too far apart (>50 cM or mu) then they are unlinked but syntenic = located on the same chr • appear to assort independently
How do you calculate RF value and what does >50%
(# of recombinants/total) x100% %RF = map units - either genes are broken in linkage by a centromere (unlinked bu syntenic) - or high mu probability of a c/o is so high its as if they sort independently