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B chromosomes |
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Although these chromosomes have no known selective advantage, they have several unusual behaviors that allow them to be maintained in populations. They avoid loss as monosomics (B-loss).
They fail to
separate
(non-disjunction) at the second pollen mitosis, which results in one
sperm having two B chromosomes while the other has none. In
addition,
the sperm with two Bs tends to fertilize the egg (preferential
fertilization), which goes on to form the embryo. 
I am interested in
these behaviors and what contributes to them. Clearly, the B
chromosome possesses factors or structures that promote these
behaviors, but the Bs also use the machinery encoded in the A
genome. 
In order to facilitate the study of B chromosomes, I use translocations
of B chromosomes with A chromosomes (B-A translocations). This
allows
the use of phenotypic markers, which are located on the A segment of
the translocation. In an appropriate genetic background, the
progeny of cross of a B-A male onto a tester female will allow for
accurate genotyping relative to the B-A chromosome. Using a color
marker on the B-A chromosome, B-loss will result in colorless (cl)
kernels. Normal disjunction results in full colored (CL) kernels;
these are euploid. Non-disjunction results in two classes of
kernels. Those with hyperploid embryos (HR) have a colored embryo
but colorless endosperm. Those with hypoploid embryos (HO) have a
colorless embryo and colored endosperm. 
07/21/09