Double Reduction In Autotetraploids

Four events must occur.

1. quadrivalent formation
2. crossover between centromere and locus
3. two heteroallelic chromosomes go to the same pole at Anaphase I(non-disjunction).
4. two sister chromatids go to the same pole at Anaphase II (double-reduction).

Quadrivalent formation at meiosis I - Event 1

Chiasma form - Event 2

Recominant chromosomes

In 1/3 of events the hetero-allelic chromosomes will migrate to the same pole at Anaphase I.

Event 3

In the above case the heteroallelic chromosomes migrate to the same pole. The above results only occur for Adacent I segregation. When Alternate or Adjacent II segregation occurs, then hetero-allelic chromosomes do not migrate to the same pole.

Meiosis II - Anaphase II - Event 4

In 1/2 of the events from the preceding diagram, double reduction gametes develop. Otherwise we could have the following:

Event 4 did not occur