Factors controlling the dynamics of the B chromosome polymorphism in Korean rye

Abstract

In order to test if a particular rye population has a specific frequency of B chromosomes or, on the contrary, if it can tolerate Bs over a wide range of frequencies, we have studied the transmission of Bs in two Korean varieties which differ in their natural B frequencies. Synthetic populations were made for each variety which carried Bs at both the natural frequency as well as at the frequency of the alternative population. The populations were open pollinated, and the frequencies of the Bs were studied over three generations. The experiment was duplicated in two different environments and the variables of viability and fertility were also compared.Fertility was lower in the 2B than in the OB plants, and it was much lower again in the 4B ones. Viability was not dependent on the number of Bs. The results were similar for both environments and this finding argues against an adaptive role for B chromosomes.The frequency of Bs in the populations sown at their natural frequencies remained constant over the generations in both environments, while the Bs of both varieties tended to move towards their natural frequencies after they were experimentally changed.There was a strong tendency for the proportion of plants with Bs in the variety with a high natural frequency to increase, while the tendency for the proportion of plants with Bs in the variety with a low natural frequency to decrease was less. These results indicate just how strong are the forces which maintain Bs in populations in the face of their harmful effects upon fertility.In our opinion the genes that control B transmission rates are the main factors that determine the range of frequencies at which a natural population can carry B chromosomes, while the tendency to recover natural frequencies rapidly following a disturbance is due to frequency-dependent selection and to a maternal imprinting effect.

Changing sex for selfish gain: B chromosomes of Lake Malawi cichlid fish

“…While only two of the six B chromosome families provided statistically significant evidence for drive, the remaining four families were statistically consistent with the averaged transmission rate of 67%. There appears to be variation in the strength of this drive among individuals, similar to reports in characiform fish 47 , grasshoppers [48][49][50][51] , daisies 52 , rye [53][54][55] , and the mealybug [56][57][58] . As found in the mealybug, this variation may be the result of polymorphic loci in the A genome that suppress drive.…”

B Chromosomes – A Matter of Chromosome Drive

“…Notably, B non-disjunction works as well when the supernumerary chromosome of rye is introduced as an extra chromosome into S. vavilovii ( Puertas et al, 1985 ), hexaploid wheat ( Lindström, 1965 ; Müntzing, 1970 ; Niwa et al, 1997 ; Endo et al, 2008 ) or hypo-pentaploid Triticale ( Kishikawa and Suzuki, 1982 ). Hence, the B chromosome regulates the process of non-disjunction on its own ( Matthews and Jones, 1983 ; Romera et al, 1991 ).…”

Nondisjunction in Favor of a Chromosome: The Mechanism of Rye B Chromosome Drive during Pollen Mitosis

“…Thus, the B controls the process of nondisjunction by itself (Matthews and Jones, 1983;Romera et al, 1991).…”