Tetraploid Definitions
See - Haldane, J.B.S. 1930. Theoretical genetics of autoploids.
Genetics 22:359-372.
Mather, K. 1935. Reductional and equational separation
of the chromosomes in bivalents and multivalents. Genetics
30:53-78
Mather, K. 1936. Segregation and linkage in autotetraploids.
J. Genetics 32:287-314.
deWinton, D., and J.B.S. Haldane. 1931. Linkage in
the tetraploid Primula Sinensis.
Genetics 24:121-144.
Doyle, G.G. 1973. Autotetraploid gene segregation.
TAG 43:139-146.
reductional - identical chromatids, derived
from the same chromosome go to the same pole. This occurs
when that particular chromosome has not participated
in a crossover event.
equational - where non-identical chromatids
pass to the same pole. This occurs when a chromosome
has two sister chromatids that originally were on two
different homologous chromosomes, but due to a crossover
event the sister chromotids are no longer identical.
double reduction - two chromatids that are the
result of replication of DNA from the same chromosome
end up in the same gamete. Sister chromotids normally
go to the same pole at Anaphase I and then to different
poles (and different gametes) at Anaphase II. A series
of events must occur for double reduction to take place:
| a) |
a multivalent must be formed and a crossover
must occur between the centromere and the
locus of interest. This event results in a
heteroallelic chromosome. |
| b) |
By chance the two heteroallelic chromosomes
must go to the same pole at first division of
meiosis. This is called genetic non-disjunction.
This only occurs for multivalents. |
| c) |
By chance the two chromatids with the same
alleleomorph go to the same pole at second
division of meiosis. This is double reduction. |
Non-disjunction - Two heteroallelic chromosomes go
to the same pole at first division of meiosis. This can only
occur when multivalents form.
