Glossary Plant Breeding

Autonomous Controlling Element. A genetic element that seems to have both regulator
and receptor functions combined in a single unit. It enters a gene and causes unstable
mutation.
Autonomous Phenotype. A genetic trait in multicellular organisms in which only
genotypically mutant cells exhibit the mutant phenotype. Conversely, a
nonautonomous trait is one in which genotypically mutant cells cause other cells,
regardless of their genotype, to display a mutant phenotype.
Autopolyploid. An individual containing multiple copies of the same sets of
chromosomes (AAA, AAAA, AAAAA, etc). Autopolyploids have usually large stomatal
size, cell size, increased vigour, large flowers and fruits, large seed size and other
plant parts compared to their diploid counterparts. However, these diagnostics are far
from universal; many autoploids may be weak and lacking in vigour. This may be due
to the existence of an optimum level of polyploidy. In most groups, this level seems to
be achieved at fairly low levels of ploidy; but in some groups, octaploids or even
higher polyploids are still vigorous types. Autopolyploids are invariably reduced in
fertility and produce fewer seeds than their diploid counterparts due to several meiotic
complexities.
Autosyndesis. Pairing between chromosomes that belong to identical genomes. (Also see
allosyndesis).
Autotetraploid. A cell having four similar sets of chromosomes (AAAA) oranorganism
composed of such cells. Autotetraploids seem to be agriculturally more important
than any other autoploids. Because four is an even number, they can have a regular
meiosis, but this may not always be the case. In general, meiotic process is much
more complex than of diploids, which involve partition of four chromatids, one to
each of the four gametes. In an autotetraploid, five genotypes are possible at each
locus compared to only three in diploids (at two loci, the no. of possible genotypes for
tetraploids and diploids are 5 2 and 3 2 , respectively; would you like to formulate the
no. of possible genotypes in hexaploids at twoloci?). Theexpectedsegregationand
assortment in tetrasomic inheritance is much complex. Factors affecting gametic
output in tetraploids are: (a) the regularity with which tetravalents (quadrivalents) are
21