Thus, the additive effect of, for instance, 2st/2st versus 2j/2j homokaryotypes could be tested as the difference between the two means, and the dominance effect as the difference between the mean value of the 2st/2j heterokaryotype versus the average of the corresponding values for the two homokaryotypes.
For VP and VA, the linear contrasts revealed lower values for 2j*/2j* when compared to 2st/2st, and the heterokaryotype 2st/2j* was always close to the average of 2st/2st and 2j*2j*, but the differences were not statistically significant (data not shown).
1988; Krimbas and Powell 1992), could be explained by the deleterious effect of simultaneous crossovers in the inverted and proximal segments of an heterokaryotype, which favors inversions located near the centromere (Navarro et al.
Thus, selection is expected to operate against long inversions due to the semisterility of heterokaryotypes (Sturtevant and Beadle 1936; Navarro et al.
- Perhaps the most widely cited example of the SB process is the evolution of new chromosome arrangements, particularly the fixation of those for which the heterokaryotype
is less fit than either homokaryotype.
Many rearrangements have surprisingly little effect on heterokaryotype
fertility, or fail to lower fertility in natural populations even when similar rearrangements do so that have arisen in laboratory stocks.
As chromosomal inversions reduce recombination in heterokaryotypes
, they can help to preserve particular combinations of alleles within the inverted segment, mainly near inversion breakpoints (Andolfatto et al.
involving arrangement 2L-1, that is, 2L-1/2L-2 and 2L-1/2L-3, were associated with decreased egg-to-adult development times when compared with 2L/2L homokaryotypes and heterokaryotypes
involving 2L, including 2L/2L-1, in populations from the Smoky Mountains.
The additional inversion complicates pairing in heterokaryotypes
with ST and is extremely difficult to distinguish from typical SR.
This significant value, caused by an excess of heterokaryotypes
(the fixation index F was - 0.074), was not repeated in the June 1989 study.
However, in the British population the acceptance rates varied with karyotype, the [Alpha][Alpha] homokaryotypes having the highest rates of acceptance, the [Beta][Beta]'s the lowest, and the [Alpha][Beta] heterokaryotypes
Moreover, the inhibitory effects of inversion heterozygosity on the rates of recombination were taken into account, assuming Hardy-Weinberg proportions for the heterokaryotypes
. In D.