âThe wrinkled seed character that Mendel studied was R versus r on l inkage group V. The character âgreen versus yellow podâ is unambiguously Gp versus gp , also on linkage group V. Linkage between these two loci can be detected. In Mendelâs study of two- and three- factor crosses he used approximately 600 F 2 individuals. He did not present data on the combination of RR Gp Gp crossed with rr gpgp ⦠[When] lines JI15 and JI399 [ are crossed ], the recombination fraction between the R locus ⦠and Gp is 36 %, resulting in an expected segregation ratio of 9 . 6 : 2.4 : 2.4 : 1 . 6 rather than 9 : 3 : 3 : 1. Mendel would have needed about 200 plants in the âsmaller numberâ to have a 5 % statistically significant deviation from independent assortment.
Furthermore, linkage group V in pea, most likely corresponding to chromosome 3 , behaves unusually in this cross because the number of chiasmata is never greater than one; usually two or three occur. The recombination fraction calculated above is therefore the smallest that Mendel could have encountered, so it is unlikely that genetic l inkage would have been discernable in any of the crosses that Mendel examined. â
⢠Explain the 9.6:2.4:2.4:1.6 ratio expected with a 36% recombination between the R and Gp loci in the cross between lines JI15 X JI399.
Hints: (i) What extent (%) of recombination would give you a perfect 9:3:3:1 ratio? (ii) You may consult the Hall et al. (1997) paper if necessary (file [6] in Minicourse 1 folder).
⢠Does the number of chiasmata (two or three in many other Pisum sativum cultivars but 1 or 0 in the JI lines) explain Mendelâs results? Hint: What are chiasmata? What is their genetic function?
⢠Can we still trust Mendelâs conclusions about independent segregation of characters?
âThe wrinkled seed character that Mendel studied was R versus r on l inkage group V. The character âgreen versus yellow podâ is unambiguously Gp versus gp , also on linkage group V. Linkage between these two loci can be detected. In Mendelâs study of two- and three- factor crosses he used approximately 600 F 2 individuals. He did not present data on the combination of RR Gp Gp crossed with rr gpgp ⦠[When] lines JI15 and JI399 [ are crossed ], the recombination fraction between the R locus ⦠and Gp is 36 %, resulting in an expected segregation ratio of 9 . 6 : 2.4 : 2.4 : 1 . 6 rather than 9 : 3 : 3 : 1. Mendel would have needed about 200 plants in the âsmaller numberâ to have a 5 % statistically significant deviation from independent assortment.
Furthermore, linkage group V in pea, most likely corresponding to chromosome 3 , behaves unusually in this cross because the number of chiasmata is never greater than one; usually two or three occur. The recombination fraction calculated above is therefore the smallest that Mendel could have encountered, so it is unlikely that genetic l inkage would have been discernable in any of the crosses that Mendel examined. â
⢠Explain the 9.6:2.4:2.4:1.6 ratio expected with a 36% recombination between the R and Gp loci in the cross between lines JI15 X JI399.
Hints: (i) What extent (%) of recombination would give you a perfect 9:3:3:1 ratio? (ii) You may consult the Hall et al. (1997) paper if necessary (file [6] in Minicourse 1 folder).
⢠Does the number of chiasmata (two or three in many other Pisum sativum cultivars but 1 or 0 in the JI lines) explain Mendelâs results? Hint: What are chiasmata? What is their genetic function?
⢠Can we still trust Mendelâs conclusions about independent segregation of characters?
