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
a) must occur between the centromere and the
a) locus of interest. This event results in a
a) heteroallelic chromosome.

b) By chance the two heteroallelic chromosomes
b) must go to the same pole at first division of
b) meiosis. This is called genetic non-disjunction.
b) This only occurs for multivalents.

c) By chance the two chromatids with the same
c) alleleomorph go to the same pole at second
c) 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.