Generation means analysis of the twin-ear trait in maize

Abstract

The twin-ear trait in maize (Zea mays L.) is defined as having two separate ears, each enclosed within separate husks and separate shanks attached to the same node. The objective of this study was to evaluate the genetic effects for twin-ear penetrance and expressivity by using generation means analysis for twin-ear inbreds A and B, each crossed to inbreds B79 and Mo17. Progeny generation means suggested twin-ear shoot formation was recessive to single-ear shoot formation. Additive and dominance effects for penetrance were adequate in explaining the variation of genetic effects for A x B79, A x Mo17, B x B79, and B x Mo17 because the additive and dominance model accounted for 97%, 97%, 94%, and 95% of the total variation in genetic effects, respectively. All four crosses had positive additive effects and negative dominance effects estimates for penetrance that were significant and unique due to the relative unimportance of epistatic effects. Genetic effects estimates are considered unique when epistatic effects are not important. Twin-ear ear formation also was recessive to single-ear ear formation. B x B79 expressivity had a significant and unique positive estimate of additive genetic effects. Significant and unique positive estimates of additive and dominance genetic effects were found for A x B79 expressivity. A x Mo17 and B x Mo17 additive and dominance genetic effects estimates for expressivity were not unique. Twin-ear penetrance and expressivity fit the definition of a threshold trait or character in this study.