1998) reported that maize Bs accounted for approximately 4% of the total chromosome
volume and an association exists between the number of Bs and the size of heterochromatic knobs, which can mask the contribution of Bs to total genome size.
Structural rearrangements of the Y chromosome
are frequently associated with testicular dysfunction.
They've done it without any Y chromosome
A normal chromosome
is linear, with its ends protected, but with ring chromosomes
, the two ends of the chromosome
fuse together, forming a circle.
Some mammals have already lost their Y chromosome
, though they still have males and females and reproduce normally.
Three-dimensional folding provides shortcuts through the chromosome
are divided into two groups: those in which one normal chromosomal homologue is replaced by a ring equivalent, and those in which the ring chromosome
is additional to the two normal copies of that chromosome
; such a ring is termed a supernumary.
analysis using meiotic spermatogonia has revealed that T.
B or supernumerary chromosomes
are generally heterochromatic, fail to pair with the normal member of the complement (A chromosomes
) during meiosis (unlike most chromosome
mutations) and often show accumulation (i.
It is not know whether Bs in Lolium perenne drive, but several studies have shown that the more densely plants with B chromosome
are planted, the better they survive.
evolution has been a driving force in speciation in diverse groups of organisms (Stebbins, 1950; White, 1978; Grant, 1981; Coyne & Orr, 2004; Ayala & Coluzzi, 2005).
Previous cytogenetic studies on 27 species of Corixoidea have shown a noticeable karyotypic uniformity with a diploid chromosome
number of 24, a pair of m chromosomes
, and an XY/XX sex chromosome
system (male/female) (Table I) (Ueshima, 1979; Ituarte & Papeschi, 2003, 2004).
According to Sykes, the problem started about 200 to 300 million years ago among mammals' ancestors, when mutations first provided the Y chromosome
with genes that direct the embryo to develop into a male.
pairs line up, moving along spindle fibers.
Vandiver later joined the staff of the MIT COEP and has worked with the program to design a learning activity for students based on the kits called "The Shape of Life: From Helix to Chromosome