The goals of this study were to (i) estimate B chromosome
polymorphisms based on their occurrence, morphology, and frequency in maize landraces from Southwest China, (ii) provide evidence for the evolution of maize landraces from Southwest China, and (iii) infer the geographical origin of landraces in southwest China.
Ward and colleagues had previously shown that two Y chromosome
genes--Sry and Eif2s3y--are crucial for male mouse development.
Instead, they showed that the low variation can be explained by intense natural selection, that is, a strong evolutionary pressure to weed out bad mutations that ended up trimming the chromosome
down to its essentials.
Summary: TEHRAN (FNA)- Chromosomes
, the molecular basis of genetic heredity, remain enigmatic 130 years after their discovery in 1882 by Walther Flemming.
The initial analysis of 30 cells showed a nonmosaic male karyotype with all cells carrying one normal homologue of chromosome
9 and one ring chromosome
numbers of 65 well-spread plates ranged from 32-37, and the mode value was 36 (Table 1).
In the present work, we characterize different chromosome
variants using fluorescent banding and analyze the pattern of simultaneous variation in relation to climatic and geographical factors in natural populations of D.
Such variations in the number of B chromosome
between cells have been reported already for Lolium by HOVIN & HILL (1966) and for other species by POWELL & BURTON (1966); JONES (1975); RAO & PANTULU (978) and RICCI et al.
Faulkner (1972) noted that the biological implications of the distinctive traits of Cyperaceae pollen development and chromosome
structure are not fully appreciated or understood.
The male diploid chromosome
number of Heteroptera ranges from 2n= 4 (Lethocerus sp.
Damaging mutations may be corrected through recombination, when chromosomes
from the mother sidle up to their counterparts from the father and exchange genetic material.
C) The chromosomes
line up along the spindle fibers.