Polyploidy
Why would any species want to have more than one gene
for any trait?
plants spontaneously undergo autopolyploidy,
. . . a mechanism for creating more than one
gene per trait,
. . . with one gene for the trait
per chromosome.
In autoploidy, meiosis is interrupted
metaphase I is 2n chromosomes (aligned as pairs)
. . -with 2 chromatids per chromosome
telophase, cytokinesis suspended
nuclear material is still
. . -2n chromosomes,
. . -2 chromatids per chromosomes
metaphase II is 2n chromosomes (aligned unpaired)
. . -with 2 chromatids per chromosome
. . -anaphase separates chromatids
telophase, cytokinesis suspended
nuclear material is now
. . -4n chromosomes,
. . -1 chromatid per chromosome
without cytokinesis,
. . -cell returns to G-1
. . -then S-1 with replication
nuclear material is now
. . -4n chromosomes,
. . -2 chromatids per chromosome
the plant is now 4n rather than 2n!
range of environmental conditions tolerated
. . . can be broken into 2n+1
sub-ranges,
. . . where n = number of genes
or chromosomes.
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© 2004 Prof. LaFrance, Ancilla College