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Ten stuttering and 10 nonstuttering subjects performed self-paced rhythmic tasks with the finger and jaw and were asked to repeat "ah." The tasks were performed at three rates: "comfortable" rate; and "slightly higher" and "slightly lower" than comfortable, but still in the comfortable range. The stutterers performed each of the three tasks more slowly than the nonstutterers and were less variable than nonstutterers. The reduced rates and more constrained variability of the stutterers were interpreted as manifestations of less flexible systems, which may be more susceptible to breakdown.

The genetic analyses of indices relating to distance alignment and accommodative convergence are presented. This approach is important in understanding the contribution of genetic factors to observed individual differences for these measures. Abnormalities of either of these two components results in a tendency towards either a convergent or divergent position of the eyes (relative to the position of fusional demand) and thus places an additional load or strain on the other components of the binocular mechanism which must compensate for this potential disruption. If compensation is inadequate to maintain alignment of the eyes, a manifest deviation will result. Consequently, an understanding of the aetiology of such factors underlies an understanding of the aetiology of nonparalytic strabismus. The three populations displayed different tendencies in the cover test measure. The average tendency for each of the populations was consistent with the type of deviation common to all propositi of families within each of the respective populations. The heritability of this character was similar in the three populations and was dependent on the contribution of the female parent only, but to a substantial degree (h2 = 0-42 +/- 0-12). The nature of the sex difference is at present open to speculation. The population means within generations were similar for the gradient measure of AC/A ratio. The heritability of this character (0-38 +/- 0-09) suggests that the genetic component is of substantial importance underlying individual differences for AC/A ratio.

The open-field behavior of 719 mice resulting from a diallel cross among the six lines of the DeFries selection experiment was assessed. Results of several analyses employing different models and procedures in open-field activity and defecation among these lines have predominantly additive effects. Estimates of heritability obtained from these analyses were considerably higher than previous estimates based on familial resemblance or the realized response to selection; thus estimation of heritability from diallel analyses is clearly unwarranted when selected lines are employed and the character of interest has been either directly or indirectly subjected to artificial selection.

Genetic parameters were contrasted for vergence amplitudes within three populations--esotropic, exotropic, and randomly selected populations-who differed in their incidence of subtypes of strabismus. In general, heritabilities for convergence exceeded those for divergence, and heritabilities for recovery points exceeded those for break points. Heritability estimates for diveregence amplitudes were significantly different for the random and esotropia populations, while convergence heritability estimates for these groups were similar. Thus, gene differences influencing divergence ability contributed to genetic variance for strabismus.

Mammalian albinism is known to alter neural pathways, reduce retinal pigment, and affect diverse behaviors. Mammalian circadian rhythms have been shown to depend on visual pathways, respond to light intensity and regulate many behaviors. Here we show that mice homozygous for the recessive albino or pinkeye-dilute mutations display shorter circadian rhythms than pigmented controls. We conclude that these pigment loci, or closely linked loci, influence the expression of circadian rhythms in mice.

Increases in nesting during pregnancy may be mediated by progesterone in mice. If the behaviors, maternal nesting (MN) and nesting induced by exogenous progesterone (PN), are controlled by the same physiological mechanism, it would be expected that they share a common genetic basis. The present experiment was designed to quantify the extent of genetic association between PN and MN. At Wesleyan University, baseline nesting was measured on females of 4 inbred strains. Subsequently, half of the mice in each strain received progesterone implants. There were significant increases in nesting due to progesterone treatment. After 21 days, implants were removed and nesting levels returned to baseline. The mice were mated and nesting measured throughout pregnancy. The strain rank order was the same for levels of PN and MN. The genetic correlation between PN and MN estimated from analysis of covariance within and between strains was not significantly different from 1.0. These results were replicated at the University of Iowa. The high genetic correlation implies a common physiological mechanism underlying PN and MN.

Heritability estimates for corneal power were found to be high and similar for two populations which differed in their incidence of esotropia. This similarity suggest (1) that genetic differences for corneal power do not contribute to the difference in heritability for spherical refractive error reported for these populations and (2) that this character is not a critical variable contributing to the pathophysiology of esotropia. Heritability estimates for corneal astigmatism were, in most cases, rather low. The pattern of population and sex differences among heritability estimates was consistent with those previously reported for cylindrical refractive error. These population differences in heritability suggest that they contribute to population differences found for cylindrical refractive error.

Genetic correlations measure the extent of pleiotropic effects of polygenes on pairs of characters or the closeness of linkage between sets of loci influencing the traits and held in allelic (gametic) disequilibrium. Their importance for research lies primarily in predicting correlated responses of one trait to selection based on values for another, and secondarily in analyzing the complex organization of biological systems. Genetic correlations appear to limit the rate and set the direction of multivariate evolution. In view of this, efficient methods for estimating genetic correlations may be essential for understanding the role of behavior in adaptation and for predicting behavioral change in evolution. In this paper we present methods for the estimation of genetic correlations from inbred strain comparisons. Estimates from inbred strains are relatively easy to obtain and appear to be valid when compared to those derived from more demanding parent-offspring comparisons and to correlated responses to selection.

Behavioral and physiological scores from 697 mice sampled from lines at various times during their response to bidirectional selection for divergent caudal nerve conduction velocity suggest broad-reaching behavioral effects of the gene differences among lines. Sciatic nerve conduction velocity differences as well as line differences in reflexive leg withdrawal indicate gene effects general to other peripheral nerves and to behaviors with known dependence on functional by those nerves. Independently replicated line differences for open-field activity and defecation demonstrate effects on more complex behaviors with no obvious direct relationship to peripheral nerve conduction velocity. The direction of line differences in open-field behaviors suggests that genetic variance for peripheral nerve function may contribute to genetic covariance between these behaviors.

In a quantitative genetic investigation of seven clinical tests, five pairs were significantly correlated: (1) cover test measures and corneal power, (2) corneal power and divergence recovery points, (3) convergence and divergence recovery points, (4) divergence break and recovery points, and (5) convergence break and recovery points. Common genes may account entirely for the gene influence on cover test measure; thus, parents who are above the population mean for corneal power will have offspring with a tendency toward an exodeviation (phoria). The two convergence amplitudes may depend on the same gene differences, whereas the two divergence amplitudes only partly reflect a common function, suggesting that they may be indexing somewhat different underlying physiologic mechanisms.

Newborn female mice of the C57BL/6J and BALB/cJ inbred strains and their reciprocal F1 hybrids were injected either with testosterone or with oil vehicle alone. Both the repeatablity and mean level of open-field activity scores over a 10-day test period increased in hormone-injected animals compared with controls. Increased activity due to hormonal treatment was greater in hybrid females than in inbred females. There was no consistent effect of hormonal treatment on open-field defecation.

Nocturnal animals typically display an increase in the free running period of circadian rhythms in response to light in direct proportion to intensity. Here we show that gene differences among inbred strains of mice (Mus musculus) modify the effect of constant bright light on the free running period of a circadian rhythm for wheel running activity. Individuals with the shortest free running periods in dim red light showed the greatest increases in period following exposure to bright light. These effects may be due to gene-imposed differences in the response of a circadian pacemaker to light, or they may be due to gene-imposed differences in visual system function that alter perception of light intensity.

Vectors of weights derived from principal components analysis of stan- dardized phenotypic, genetic, and environmental covariance matrices were applied to open-field behavioral scores from mice in order to obtain composite scores with maximum phenotypic (Vp), genetic (Va), and environmental (Ve)variance, respectively. Since Va associated with the composite from the genetic covariance matrix is derived as maximum, and since Vp associated with this combination cannot be as large as that associated with the phenotypic com- posite, heritability of the genetic composite must exceed that of the phenotypic composite. In addition, since Ve associated with the environmental composite is maximum and since Vp associated with this score cannot exceed Vp from the phenotypic composite, Va associated with the phenotypic composite should exceed that from the environmental composite. Thus, heritability of the pheno- typic composite scores should exceed that for the environmental composite. The predicted rank order of the heritabilities was observed. Pooled estimates of the heritabilities of the genetic, phenotypic, and environmental components were 0.24, 0.19, and 0.17, respectively.

In segregating F(2), F(3), and F(4) generations, albino mice had lower activity and higher defecation scores than pigmented animals when tested in a brightly lighted open field. These differences persisted when members of an F(5) generation were tested under white light, but largely disappeared under red light. Thus it was concluded that there is a major gene effect on the quantitative traits of open-field activity and defecation which is mediated by the visual system and that albino mice are more photophobic than pigmented mice under conditions of bright illumination.