HOMOPLASY AND THE CHOICE AMONG CLADOGRAMS

Abstract Cladistic data are more decisive when the possible trees differ more in tree length. When all the possible dichotomous trees have the same length, no one tree is better supported than the others, and the data are completely undecisive . From a rule for recursively generating undecisive matrices for different numbers of taxa, formulas to calculate consistency, rescaled consistency and retention indices in undecisive matrices are derived. The least decisive matrices are not the matrices with the lowest possible consistency, rescaled consistency or retention indices (on the most parsimonious trees); those statistics do not directly vary with decisiveness. Decisiveness can be measured with a newly proposed statistic, DD = − S )/( − S ) (where S = length of the most parsimonious cladogram, = mean length of all the possible cladograms for the data set and M = observed variation). For any data set, can be calculated exactly with simple formulas; it depends on the types of characters present, and not on their congruence. Despite some recent assertions to the contrary, the consistency index is an appropriate measure of homoplasy (= deviation from hierarchy). The retention index seems more appropriate for comparing the fit of different trees for the same data set.     

姐妹染色单体互换在鹌鹑胚胎细胞染色体间及染色体上的分布

SCE在鹌鹑胚胎细胞间的分布为Poisson分布;在染色体间的分布是非随机的,与染色体的相对长度成正相关（P<0.05）,但也不完全按各染色体的相对长度分布。着丝粒区的SCE相对很高,按染色体的相对长度分布。胚胎的不同性别对每个细胞的SCE平均值无显著影响,但对性染色体Z上的SCE是否有影响还不能做出肯定的结论。     

低水势下冬小麦胚芽鞘长度与叶片的渗透调节能力及大田产量关系的研究

本文以７个抗旱性不同的冬小麦品种（系）为材料,研究了低水势下芽鞘长度与大田干旱条件下叶片的渗透调节能力及大田产量的关系。结果表明：低水势下芽鞘长度与叶片的渗透调节能力及产量有极为密切的关系。为冬小麦抗旱鉴定及抗旱个体筛选提供了一个良好的指标。     

麝,獐,麂和鹿间线粒体DNA的差异及其系统进化研究

用PCR技术和序列测定方法从线粒体DNA上得到367bp的细胞色素b基因片段序列。分析得出,麝与獐、麂和鹿的遗传差异在12．53％～14．44％之间,处在科间变化范围之内,在分子水平上进一步表明麝应作为一独立科;獐、麂和虎间序列的平均差异为10．28％,属于业科间的差异,与形态研究结果一致。麝、獐、麂和鹿的系统进化中,麝约在600万年前与鹿科分歧,而鹿科的三个亚科是在350～500万年开始分歧;麝、獐、麂和鹿共同组成一单系群．在600万年前具有一共同祖先。     

DIFFERENCES IN THE OCCURRENCE AND DISTRIBUTION OF HYDROXYPROLINE-PROTEINS AMONG THE ALGAE

Fifty algae from seven phyla have been examined in order to determine whether they contain protein-bound hydroxyproline and whether this hydroxyproline is concentrated in the cell wall. Green algae, with the exception of Nitella, all contain hydroxyproline, and in most cases it is concentrated in the cell wall. Hydroxyproline is also present in low levels in the brown algae, but here it is concentrated in the soluble proteins. Red algae contain no hydroxyproline. The presence of hydroxyproline in blue-green algae is variable, but when present the levels are low. It appears, then, that the major algal phyla differ with respect to the distribution and occurrence of hydroxyproline-proteins.