Cencepts - Part II

Duplex - AAaa genotype. Random chromosome segregation results in a 1/6AA:4/6Aa:1/6aa gametic ratio for random chromosome segregation.

Triplex - AAAa genotype. The random chromosome segregation ratio is 1/2AA:1/2Aa.

Simplex random chromatid segregation - requires multivalent formation, crossover between centromere and locus, and non-disjunction at meiosis I. Double-reduction can occur a maximum of 1/6 of resulting gamets.

These are the only double reductional types = 4/8 = 1/2; e/2 = 1/2; when e=2p=1. For this alternate segregation.

Then a=1/3 because only one form of Adjacent I segregation results in non-disjunction. The other Adjacent segregation and the Alternate segregation cannot result in double-reduction. "e" can be a maximum of unity, e=1 when a crossover occurs at each meiotic event. Due to segregation when e=1, only 1/2 of the gametes are double-reduction types. a=(qea)/2; If q=1, e=1, and a=1/3, then a=1/6 as a maximum.

a = 1/6 for maximal equation segregation.

However q may be less than one, meaning that multivalents would not always form. "e" might be less than 1 when the locus is close to the centromere such that crossover frequency is reduced. In these cases a would be smaller than 1/6. In fact, there is no exact segregation ratio for autotetraploids because a varies with distance of the locus from the centromere. For the simplex segregation ratio with chromatid segregation we have the following ratio:

Duplex random chromatid segregation.

Triplex random chromatid segregation.