Department of Forestry and Resource Management, University of California, Berkeley, California 94720.
Genetics. 1986 May;113(1):115-34. doi: 10.1093/genetics/113.1.115.
The dependence of heterosis at isozyme loci on inbreeding and crossbreeding was studied in 10-yr-old trees of knobcone pine (Pinus attenuata Lemm.). Heterozygosity was determined at 24 polymorphic isozyme loci and related to the rate of vegetative growth and cone production. The inbreds, created by selfpollination, had 46% of the heterozygosity of their mothers; the crossbreds, created by interpopulation crossing, had 155% of the heterozygosity of their mothers. Within the crossbreds, heterozygosity was positively correlated with trunk growth, but negatively correlated with cone production. Results in the crossbreds, however, were strongly influenced by a few individuals that showed unusually slow growth, high reproduction and low heterozygosity. Without those individuals, there was no relationship of heterozygosity to either growth or reproduction.-Within the inbreds, heterozygosity was positively correlated with both trunk growth and cone production. Each locus that was heterozygous in the mothers was calculated to mark about 3% of the genome for identity by descent in the inbred progeny; the total proportion of the genome marked was between 10 and 11%. Using these estimates to relate heterozygosity to the inbreeding coefficient (F) gave estimates of inbreeding depression per unit of F that fell within the range of published values for conifers. The strength of heterosis found among the inbreds suggests that single-locus or multilocus overdominance should be exceedingly difficult to detect in natural populations of predominantly outcrossing species.
在 10 年生的华山松（Pinus attenuata Lemm.）树木中，研究了同工酶位点杂种优势对自交和杂交的依赖性。在 24 个多态同工酶位点上测定了杂合性，并将其与营养生长和球果生产的速度相关联。自交系是通过自花授粉产生的，其杂合性为母本的 46%；杂交系是通过种群间杂交产生的，其杂合性为母本的 155%。在杂交系中，杂合性与树干生长呈正相关，但与球果生产呈负相关。然而，杂交系中的结果受到少数个体的强烈影响，这些个体表现出异常缓慢的生长、高繁殖和低杂合性。没有这些个体，杂合性与生长或繁殖之间就没有关系。在自交系中，杂合性与树干生长和球果生产都呈正相关。每个在母本中为杂合的位点都被计算为在自交后代中与亲本同源的基因组标记约 3%；标记的基因组总比例在 10%到 11%之间。使用这些估计值将杂合性与自交系数（F）相关联，得出的每个 F 单位的自交衰退估计值在发表的针叶树值范围内。在自交系中发现的杂种优势强度表明，在主要为异交的物种的自然种群中，单个或多个位点的超显性应该极难被检测到。
