GENE20001 Lecture Notes - Lecture 3: Genetic Linkage, Mendelian Inheritance, Spermatogenesis
Genetic linkage becomes difficult to detect when RF approaches 50%.
•
Genes far apart enough on the same chromosome might sort independently.
•
Even if 2 genes assort independently, there will be 25% of each recombinant. Then the RF
would be 50% anyway, which is a hallmark of independent assortment/lack of genetic linkage.
•
Just because RF is 50% doesn't mean genes are not on same chromosome. They may be
physically linked (on same chromosome)
•
More crossing over --> more recombinant gametes --> more recombinant progeny
•
○
Linkage between pr and vg is incomplete (RF = 10.7%) → meiotic recombination
permissive
▪
When F1= female, both parentals and recombinants recovered
○
Linkage between pr and vg is complete (RF = 0%) → meiotic recombination
restrictive - no meiotic recombination in Drosophila males (achiasmatic
spermatogenesis)
▪
When F1= male, only parentals recovered
○
e.g. pr-vg testcross in Drosophila
•
e.g. achiasmatic spermatogenesis
▪
e.g. achiasmatic oogenesis
▪
Meiotic recombination does not occur - no chiasmata
○
Common in male higher Diptera (e.g. flies) and female Lepidoptera (butterflies and
moths)
○
Useful for assigning genes to a chromosome, because genes on same chromosome
always transmitted as a block.
○
Recombination permissive sex needed for estimating distance between linked genes.
○
Assigning genes to a chromosome: chiasmatic vs achiasmatic
Achiasmatic gametogenesis
•
Physical linkage vs genetic linkage
3 Mapping genes
Monday, 3 March 2014
12:29 PM
Genetics Page 1
Document Summary
Genetic linkage becomes difficult to detect when rf approaches 50%. Genes far apart enough on the same chromosome might sort independently. Even if 2 genes assort independently, there will be 25% of each recombinant. Then the rf would be 50% anyway, which is a hallmark of independent assortment/lack of genetic linkage. Just because rf is 50% doesn"t mean genes are not on same chromosome. They may be physically linked (on same chromosome) More crossing over --> more recombinant gametes --> more recombinant progeny e. g. pr-vg testcross in drosophila. When f1 = female, both parentals and recombinants recovered. Li(cid:374)kage (cid:271)et(cid:449)ee(cid:374) pr a(cid:374)d (cid:448)g is i(cid:374)(cid:272)o(cid:373)plete (cid:894)rf = (cid:1005)(cid:1004). 7%(cid:895) (cid:373)eioti(cid:272) re(cid:272)o(cid:373)(cid:271)i(cid:374)atio(cid:374) permissive. Li(cid:374)kage (cid:271)et(cid:449)ee(cid:374) pr a(cid:374)d (cid:448)g is (cid:272)o(cid:373)plete (cid:894)rf = (cid:1004)%(cid:895) (cid:373)eioti(cid:272) re(cid:272)o(cid:373)(cid:271)i(cid:374)atio(cid:374) restrictive - no meiotic recombination in drosophila males (achiasmatic spermatogenesis) Meiotic recombination does not occur - no chiasmata e. g. achiasmatic spermatogenesis. Meiotic recombination does not occur - no chiasmata e. g. achiasmatic spermatogenesis e. g. achiasmatic oogenesis.
