Parental Mating Research Articles

Genetic Diversity Patterns in Chinese Soybean Cultivars Based on Coefficient of Parentage

China released 651 soybean [Glycine max (L.) Merr.] cultivars from 1923 to 1995. However, their diversity is not well characterized. The objective of this study was to quantify genetic diversity in Chinese cultivars via coefficient of parentage (CP), and the relative importance of geographical growing region, province of origin, intended cropping system, era of release, and breeder preferences in determining that diversity. A very low mean CP of 0.02 was found in Chinese soybean cultivars, suggesting the presence of a potentially high level of genetic diversity in Chinese soybean breeding. Cultivar pools from each of the three growing regions of China were almost completely unrelated to each other and exhibited low within‐region mean CP values (<0.06). Similarly, mean CP values within‐ and between‐provinces were low (0–0.2). Cropping systems and release eras also exhibited low within‐ and between‐CP relationships (all <0.07). The low CP values detected here for Chinese soybean breeding resulted from Chinese breeder initiatives to introduce new germplasm into applied Chinese breeding since the 1970s and from a strong tendency to avoid the mating of related parents. Half‐ and full‐sib matings and backcrossing are almost absent from Chinese pedigrees. Although mean CP for cultivars was low, cluster analysis proved to be a surprisingly effective discriminator of diversity patterns. This analysis assigned 270 cultivars to 20 clusters explaining 41% of the total variability in CP. Clusters were almost completely unrelated to each other and could be used as a basis for selection of parents for breeding. Pedigree analysis revealed that more than 30 cultivars grown currently in China trace to U.S. stocks. This successful use of U.S. germplasm in China may provide an important example for future U.S. breeding strategy.

MOLECULAR TOOLS FOR DETECTING GENETIC DIVERSITY

The diversity that resides within living organisms, often referred to as biodiversity, is essential for sustained existence and provides the raw materials for agriculture, biotechnology and medicine. Both its conservation and utilisation require knowledge of existing variation. Molecular tools provide valuable data on diversity through their ability to detect variation at the DNA level. Although this has many important applications, the overview presented here focuses on the use of molecular techniques for detecting genetic differences, distinguishing between individuals and for identification. Identification is of fundamental importance in diversity studies in a variety of different ways, For evaluation of species diversity, it is essential that individuals can be classified accurately The identification of taxonomic units and endangered species, whose genetic constitution is distinct from their more abundant relatives, is important in the development of appropriate conservation strategies. In population studies, being able to identify whether two individuals are from the mating of specific parents and estimating the degree of relatedness among individuals, is helpful for the determination of social behaviour, reproductive success and mating choice. Identification is of importance in studying clonal organisms and the roles of sexual and asexual reproduction, where the definition of population units and different genetic lines may be difficult. From a more practical standpoint, identification of who breeds with whom is important for the management of small populations. Moreover, being able to detect gene flow. introgressior and contamination from unwanted outcrossing (genetic pollution) is crucial for the attainment of purity and has become a central issue in debate over the safety of genetically modified organisms, Identification is also a key issue for forensic purposes, for example, in the confiscation and legal protection of illegally imported, collected or commercially exploited material. A number of different techniques are available for identifying genetic differences between organisms. The choice of technique for any one specific use will depend upon the material being studied and the nature of the questions being addressed. Molecular techniques differ in the way they sample within the genome and in the type of data that they generate. For classification based on known evolutionary history, analysis of DNA sequences is the best approach, whilst multi-locus profiling techniques, such as VNTRs (variable number of tandem repeats) and AFLPs (amplified fragment length polymorphisms), or microsatellite genotyping, have much to offer for fingerprinting individuals and identity assignment. For practical usage, only a few techniques are suitable for applications where different laboratories must be able to reproduce results and analyse them using standardised scoring and data analysis methods. Molecular data may also need to be automated and amenable for entry into databases.

Statistical confidence in parentage analysis with incomplete sampling: how many loci and offspring are needed?

We have recently presented models to estimate parentage in breeding systems with multiple mating and incomplete sampling of the candidate parents. Here we provide formulas to calculate the statistical confidence and the optimal trade-off between the number of loci and offspring. These calculations allow an understanding of the statistical significance of the parentage estimates as well as the appropriate sampling regime required to obtain a desired level of confidence. We show that the trade-off generally depends on the parentage of the putative parents. When parentage is low, sampling effort should concentrate on increasing the number of loci. Otherwise, there are similar benefits from increasing the number of loci or offspring. We demonstrate these methods using genetic data from a nest of the bluegill sunfish (Lepomis macrochirus).

Investigation into the mode of inheritance of allozyme and random amplified polymorphic DNA markers in tilapia Oreochromis mossambicus (Peters)

Feral Australian Oreochromis mossambicus (Peters) (Pisces: Cichlidae) and an interspecific hybrid population (most probably originally derived from crosses of O. mossambicus and O. niloticus stocks) were used as model organisms to study the inheritance patterns of 24 allozyme loci and 31 random amplified polymorphic DNA (RAPD) loci in tilapia. Single-paired matings of parents of known genotype were used to generate families, and 10–15 full-sib offspring from each mating were used to test for mode of inheritance. The majority of allozyme and RAPD loci tested segregated in a Mendelian fashion. Allozyme markers in general showed co-dominant inheritance patterns, while RAPD markers conformed to expectations for band presence/absence under a dominant allele model. Although only a small number of families and offspring were used, the results highlight the suitability of allozymes and RAPDs as genetic markers for population analysis in tilapia.

The Use of Case-Parent Triads to Study Joint Effects of Genotype and Exposure

Most noninfectious disease is caused by low-penetrance alleles interacting with other genes and environmental factors. Consider the simple setting where a diallelic autosomal candidate gene and a binary exposure together affect disease susceptibility. Suppose that one has genotyped affected probands and their parents and has determined each proband's exposure status. One proposed method for assessment of etiologic interaction of genotype and exposure, an extension of the transmission/disequilibrium test, tests for differences in transmission of the variant allele from heterozygous parents to exposed versus unexposed probands. We show that this test is not generally valid. An alternative approach compares the conditional genotype distribution of unexposed cases, given parental genotypes, versus that of exposed cases. This approach provides maximum-likelihood estimators for genetic relative-risk parameters and genotype-exposure-interaction parameters, as well as a likelihood-ratio test (LRT) of the no-interaction null hypothesis. We show how to apply this approach, using log-linear models. When a genotype-exposure association arises solely through incomplete mixing of subpopulations that differ in both exposure prevalence and allele frequency, the LRT remains valid. The LRT becomes invalid, however, if offspring genotypes do not follow Mendelian proportions in each parental mating type-for example, because of genotypic differences in survival-or if a genotype-exposure association reflects an influence of genotype on propensity for exposure-for example, through behavioral mechanisms. Because the needed assumptions likely hold in many situations, the likelihood-based approach should be broadly applicable for diseases in which probands commonly have living parents.

Methods for Detection of Parent-of-Origin Effects in Genetic Studies of Case-Parents Triads

When affected probands and their biological parents are genotyped at a candidate gene or a marker, the resulting case-parents-triad data enable powerful tests for linkage in the presence of association. When linkage disequilibrium has been detected in such a study, the investigator may wish to look further for possible parent-of-origin effects. If, for example, the transmission/disequilibrium test restricted to fathers is statistically significant, whereas that restricted to mothers is not, the investigator might interpret this as evidence for nonexpression of the maternally derived disease gene-that is, imprinting. This report reviews existing methods for detection of parent-of-origin effects, showing that each can be invalid under certain scenarios. Two new methods are proposed, based on application of likelihood-based inference after stratification on both the parental mating type and the inherited number of copies of the allele under study. If there are no maternal genetic effects expressed prenatally during gestation, the parental-asymmetry test is powerful and provides valid estimation of a parent-of-origin parameter. For diseases for which there could be maternal effects on risk, the parent-of-origin likelihood-ratio test provides a robust alternative. Simulations based on an admixed population demonstrate good operating characteristics for these procedures, under diverse scenarios.

Influence of Parental Concordance for Psychiatric Disorders on Psychopathology in Offspring

To examine the influence of parental mating types for substance abuse and anxiety/affective disorders on the risk of psychopathology among child and adolescent offspring. Emotional and behavioral disorders were assessed in offspring, aged 7 to 17 years, of male and female parents who served as probands from a family study of comorbidity of substance abuse and anxiety disorders. The findings indicated that (1) patterns of psychopathology among offspring were similar for mothers and fathers; (2) spouse concordance for psychopathology was greater among parents with substance abuse than among those with anxiety, particularly among female substance abusers; (3) there was a direct relationship between the number of affected parents and the magnitude of psychopathology in children, particularly with respect to the anxiety disorders; and (4) by contrast, rates of conduct disorder were elevated only among offspring of dually affected parents, irrespective of the specific parental disorders. These findings underscore the importance of the contribution of both mothers and fathers, particularly those with concordance for psychiatric disorders, to the development of psychopathology in offspring.

Development of Amplified Fragment Length Polymorphism (AFLP) Markers Suitable for Genetic Linkage Mapping of Catfish

Genomic research requires many molecular markers for construction of the genetic linkage map and for marker-assisted selection (MAS). Amplified fragment length polymorphism (AFLP) markers are inherited with Mendelian expectations in catfish and, thus, are suitable for use in gene mapping and MAS. To identify large numbers of AFLP markers, 64 primer combinations were tested to generate AFLP patterns between channel catfish Ictalurus punctatus and blue catfish I. furcatus. The 64 primer combinations amplified 7,871 bands, of which 3,081 were polymorphic between the two mating parents of channel catfish and blue catfish used to produce the reference families for mapping analysis. The primer combinations that produced fewer bands showed higher rates of polymorphism. Of the 64 primers, 53 primer combinations produced clean and reproducible AFLP profiles. Nine primer combinations produced fair AFLP profiles. The remaining two primers produced poor AFLP profiles with intensive background bands. The 53 excellent primer combinations produced 2,572 AFLP markers. These markers are suitable for use in gene and quantitative trait loci mapping of catfish by using the interspecific hybrid system. Analysis of genetic variations among strains of channel catfish indicated that AFLP should also be a valuable tool for genetic resource and population analyses in fish.

黒毛和種牛のバンド3蛋白欠損症の遺伝学的コントロール

To control the hereditary deficiency of red cell band 3 with spherocytosis inherited by an autosomal incomplete dominant mode in Japanese black cattle the dams were mated with assumptive non-carrier bulls. The dam genotypes were determined by the osmotic fragility of red cells and their offsprings, while the sire genotypes were supposed based on the previous production of affected offsprings. The definitive genotypes were determined by the causal DNA mutation. Out of 12 calves produced by mating of heterozygous parents before controlling, two were affceted. After the genetic control however, there was no affected case in 9 calves produced. The gene frequencies were 54% and 22% before and after the control, respectively.

Effect of metalaxyl on formation and germination of oospores of Phytophthora infestans

Oospores of Phytophthora infestans were produced in potato leaf discs floating on metalaxyl solution (100 μg mL−1 a.i.) and inoculated with all combinations of two metalaxyl‐sensitive and two ‐resistant parental isolates. Numbers of oospores produced varied between different matings, depending on parents, in the absence of the fungicide and when metalaxyl was added 0, 7, 14 and 21 days after inoculation. Oospores were not produced when metalaxyl was added at the time of inoculation (0 days) when either one or both parents were sensitive to metalaxyl. In two of three such matings further oospore formation was arrested when metalaxyl was added either 7 or 14 days after inoculation. Oospores extracted from leaf discs 14, 21 and 28 days after inoculation were assessed for germination on water agar after 21 days. Germination of oospores from water control treatments varied between 6 and 30% depending on the cross. Germination was significantly reduced in oospores of metalaxyl‐sensitive parents extracted 28 days after inoculation of leaf discs treated with metalaxyl 0, 7 and 14 days after inoculation compared with the 21‐day treatment. Minimal differences in germination were observed for oospores from the mating of resistant parents irrespective of metalaxyl treatment, although germination was generally low, not exceeding 8.5%.

A Log-Linear Approach to Case-Parent–Triad Data: Assessing Effects of Disease Genes That Act Either Directly or through Maternal Effects and That May Be Subject to Parental Imprinting

We describe a log-linear method for analysis of case-parent-triad data, based on maximum likelihood with stratification on parental mating type. The method leads to estimates of association parameters, such as relative risks, for a single allele, and also to likelihood ratio chi2 tests (LRTs) of linkage disequilibrium. Hardy-Weinberg equilibrium need not be assumed. Our simulations suggest that the LRT has power similar to that of the chi2 "score" test proposed by Schaid and Sommer and that both can outperform the transmission/disequilibrium test (TDT), although the TDT can perform better under an additive model of inheritance. Because a restricted version of the LRT is asymptotically equivalent to the TDT, the proposed test can be regarded as a generalization of the TDT. The method that we describe generalizes easily to accommodate maternal effects on risk and, in fact, produces powerful and orthogonal tests of the contribution of fetal versus maternal genetic factors. We further generalize the model to allow for effects of parental imprinting. Imprinting effects can be fitted by a simple, iterative procedure that relies on the expectation-maximization algorithm and that uses standard statistical software for the maximization steps. Simulations reveal that LRT tests for detection of imprinting have very good operating characteristics. When a single allele is under study, the proposed method can yield powerful tests for detection of linkage disequilibrium and is applicable to a broader array of causal scenarios than is the TDT.

Inheritance of RAPD molecular makers in lake trout Salvelinus namaycush

Inheritance patterns of randomly amplified polymorphic DNA (RAPD) phenotypes were tested in 13 full‐sib families of lake trout Salvelinus namaycush. Single‐pair matings of parents with known phenotypes were made, and up to 20 progeny of each mating were used to test inheritance patterns. Seven RAPD primers amplified 13 polymorphic bands. With the exception of one family, expected segregation ratios for dominant Mendelian genetic traits were observed. Our results support previously reported findings that RAPD markers can be considered Mendelian traits and therefore could be used for analysis of genetic population structure.

Morphological and cytogenetic characteristics of intergroup hybrids between closely related mating groups of the Closterium ehrenbergii species complex (Desmidiales, Chlorophyta)

SUMMARYFive F1 hybrid strains were established from rare survivors in intergroup crosses between three closely related mating groups (A, B and H) of the Closterium ehrenbergii Meneghini ex Ralfs species complex. Cell sizes of these five strains studied under our standard culture conditions were compared to those of their parental stains and also to the total range of cell‐size variation in each mating group. All five F1 strains were larger in mean cell width than their parental strains. In cell length, three of them were larger than, one was the same as, and the other was intermediate between their parental strains. Their cell sizes were always larger than the range of their respective smaller parental mating group and three of them were larger than the range of their respective larger parental mating group.

Plasma von Willebrand factor antigen concentration as a predictor of von Willebrand’s disease status in German Wirehaired Pointers

Objective To evaluate the use of plasma von Willebrand's factor (vWF) concentration as a screening test for inherited von Willebrand's disease (vWD) in German Wirehaired Pointers (GWHP). Design Prospective study. Sample Population Plasma samples from 467 GWHP. Procedure Plasma vWF concentrations were measured as vWF antigen (vWF:Ag), using ELISA, and test values were used to estimate prevalence of vWD in GWHP and predict parental vWD status. Test results of progeny from matings of carrier and noncarrier parents were then compared with the predicted outcome of such matings. Results 376 (81%) GWHP were classified as VWD noncarriers, 58 (12%) as carriers, and 5 (1%) as affected with VWD. An additional 28 (6%) GWHP could not be classified on the basis of plasma VWF:Ag concentration. The observed outcome of tests of 213 pups was not significantly different from that predicted on the basis of parental VWWF:Ag concentration. The predictive value of a positive test result (vWF: Ag% < 50) for identifying VWD carriers was 0.89. Clinical Implications Plasma vWF:Ag concentration was an effective predictor of genetic status for the vWD trait, and for the outcome of matings between carriers and noncarriers of vWD in this study of GWHP. (J Am Vet Med Assoc 1996;209:930-933)

Antibody Response to Sheep Red Blood Cells in a Major Histocompatibility (B) Complex Aneuploid Line of Chickens

An integral part of the immune response is the production of antibodies specific for different antigenic challenges. Genes of the MHC encode products that regulate immunity. This study utilized the FCT-15 line of chickens, which is aneuploid for the chromosome containing the ribosomal RNA genes (rDNA) and the MHC or B complex to determine whether an antibody response to SRBC would vary as a function of B complex gene dose. Mating of trisomic parents (B15B15B15) animals produced progeny having either a disomic (B15B15), trisomic (B15B15B15), or tetrasomic (B15B15B15B15) B complex dosage. The number of B/rDNA chromosomes, and thus the B complex dosage, was determined by feather pulp nucleolar typing of chicks at hatch. A 5% SRBC antigenic challenge, which induces a T cell-dependent antibody response, was injected at 6 wk of age. Samples taken prior to SRBC injection as well as 5, 8, and 12 d postinjection were assayed for total and mercaptoethanol-resistant antibody. Peak antibody titers (log2), day of peak titer and rate of titer decline were calculated using a quadratic equation for each bird. Differences among the three B complex dosages were evaluated by analysis of variance. Antibody titers rose from 5 to 8 d postinjection and declined thereafter without significant differences among the three B complex doses. Calculations from the quadratic equations showed that B complex dose affected neither peak antibody titer nor day of peak titer. However, trisomic and tetrasomic animals had significantly more rapid rates of decline from the maximum titer. In aneuploid chickens, changes in antigen processing, antigen presentation, or persistence of processed antigen may maintain levels of antibody production found in disomic chickens and explain the more rapid decline of titer.

Inhalation teratology and two-generation reproduction studies with 1,1-dichloro-1-fluoroethane (HCFC-141 b)

HCFC-141b is one of the chemicals being considered as a replacement for CFC 11 in solvent and foam-blowing applications. Teratology studies were conducted in both rats and rabbits and a two-generation reproduction inhalation toxicity study was conducted in rats. The pregnant rabbits were exposed to levels of 0 (control), 1400, 4200 and 12,600 ppm HCFC-141b from day 7 today 19 of gestation (6 hr/day). There was no evidence of developmental or teratogenic effects on the foetuses. The pregnant rats in the teratology study were exposed to levels of 0 (control), 3200, 8000 and 20,000 ppm from days 6 to 15 of gestation (6 hr/day). In the 20,000 ppm exposure group, there was an increase in implantation losses; furthermore, in this group, foetal weights tended to be lower than controls. As with the rabbits, there was no evidence of a teratogenic effect. The reproduction study was conducted at exposure levels of 0, 2000, 8000 and 20,000 ppm, 7 days/wk starting approximately 10 wk before the first pairing. Adult rats exposed at 20,000 ppm (and, to a lesser extent, those exposed to 8000 ppm) showed increases in water intake, slight increases in food consumption, and decreases in body weight. Following the mating of the F0 parents, there were fewer litters in the 20,000 ppm exposure level group than in controls. When these parents were then paired with different partners, again, the number of litters was lower in the 20,000 ppm group, although most of the animals that did not produce litters the first time mated successfully the second time. When the F1 animals were mated to produce the second generation, the number of litters was comparable for all groups. In the second F0 mating and the F1 mating, the number of pups per litter was lower at 20,000 ppm; although birth weights were comparable, body weight gain tended to be slower in the high-level exposure group. Survival was good in all groups. At 8000 ppm no significant effects were observed in the pups and only minimal signs in the adults. The 2000 ppm exposure level represented a clear no-observed-effect level for all indices.

Quantitative analysis of the effect of selection history on sugar yield adaptation of sugarcane clones

An objective of the CSR sugarcane breeding programme in Australia was to assess the scope for broadening the genetic base of the commercial sugarcane germ plasm through interspecific hybridization with Saccharum spontaneum clones. The contribution of both selection history and S. spontaneum to sugar yield and its components was investigated in the germ plasm pool assembled. The analysis was conducted on a data-set of 256 clones, consisting of parents and full-sib families generated from 32 biparental crosses, tested in six environments. The minimum number of generations back to S. spontaneum ancestor in the clone's pedigree was used as a germ plasm score. The geographical origin and selection history of each parent and their use in the biparental crosses were used to develop a selection history score for parents and offspring. The variation for seven attributes, cane yield, commercial cane sugar %, sugar yield, stalk number per stool, stalk weight, fibre % and ash % juice was partitioned according to the germ plasm and selection history scores. Significant (P<0.05) clone variation and clone x environment interaction for all attributes was present. The germ plasm scores accounted for a significant (P<0.05) component of the clone variation for all of the attributes except cane yield. There was an increase in sugar yield with an increase in the minimum number of generations back to a S. spontaneum clone. The selection history groups accounted for a high proportion of the variation among parental clones for all of the attributes except cane yield. This suggested that parents were the outcome of strong selection pressure for the commercial cane attributes. However, the selection history groups for the offspring produced by random mating of parents did not account for a high proportion of the variation for the attributes. Using the mixture method of classification we partitioned the 256 clones into five groups for patterns of performance for the seven attributes across the six environments. The five groups emphasized major differences in the patterns of performance for the seven attributes across environments. The distribution of germ plasm and selection history scores in each of the five groups indicated that their patterns of performance were associated with selection history and minimum generations to S. spontaneum. Therefore, both the analysis on selection history and germ plasm scores (extrinsic classification) and the analysis on the mixture method of classification (intrinsic classification) emphasized the influence of selection history on the sugar yield of sugarcane.

INBREEDING DEPRESSION INHYDROPHYLLUM APPENDICULATUM:ROLE OF MATERNAL EFFECTS, CROWDING, AND PARENTAL MATING HISTORY

This paper examines several aspects of the expression of inbreeding depression in an outcrossing, obligately biennial plant, Hydrophyllum appendiculatum (Hydrophyllaceae). The amount of inbreeding depression detected was small during the first year of life but increased with age and had significant effects on adult size and reproductive traits. The lack of significant inbreeding depression during early growth is likely due to the overriding influence of maternal environmental effects on seed size and seedling growth. However, as maternal effects decreased with age, the seedling's own genotype became a more important determinant of its fate. To examine whether the expression of inbreeding depression was sensitive to ecological conditions, selfed and outcrossed seedlings were grown alone or with other H. appendiculatum seedlings. No inbreeding depression was detected in the plants grown alone. In contrast, under competitive conditions, outcrossed seedlings were significantly larger than selfed seedlings by the end of the first growing season. To address whether parental mating history influences the amount of inbreeding depression expressed, I examined the consequences of two successive generations of selfing on seed set and seed weight. The amount of inbreeding depression increased following the second generation of selfing. In the first generation, seed set and seed weight differed by less than 5% between selfed and outcrossed progeny. However, both traits were 15% greater for outcrossed plants after two generations. These results indicate that the alleles responsible for the reductions in these traits were not purged and suggest the action of multiple loci with deleterious effects.

Inheritance of Blood Ring, an Early Embryonic Failure in the Turkey

Blood ring describes an early embryonic failure that has been observed in a subline of Wrolstad Medium White turkeys. The condition can be detected by candling at approximately 96 h of incubation when shell pigmentation is minimal. The condition, macroscopically visible as early as 66 h, is characterized by the presence of uncoalesced blood islands, an erythrocyte-engorged sinus terminalis, and the absence of an extra-embryonic circulatory system. The sex ratio of progeny from the mating of heterozygous parents did not deviate from a 1:1 ratio and no blood ring embryos resulted from the matings of heterozygous males and normal females. The disorder is inherited as an autosomal recessive trait and appears to be similar to a condition observed in both normal-sized and dwarf (dw) Single Comb White Leghorn chickens. The symbol blr is suggested for the gene.

Cocaine toxicity: genetic evidence suggests different mechanisms for cocaine-induced seizures and lethality

While low doses of cocaine have been shown to decrease locomotor activity, and moderate doses produce marked increases in locomotor activity, high doses commonly produce seizures and, eventually, death. However, the biological mechanisms associated with cocaine-related death, as well as the contribution of seizure activity to death are poorly understood. This study examined the effects of a broad range of cocaine doses on acute occurrence of seizures and death in LS/Ibg (LS) and SS/Ibg (SS) mice. Large differences in sensitivity to cocaine-induced seizures were seen, with ED50 values being 41.7 and 80.9 mg/kg for the SS and LS mice, respectively. Conversely, no significant differences in cocaine LD50 values were found, being 100.7 and 107.2 mg/kg for the SS and LS mice, respectively. That these lines of mice differ substantially in convulsant responses to cocaine, but show no difference in lethal response to this drug, supports the conclusion that cocaine causes death by mechanisms distinct from those which contribute to seizures. The distinction between cocaine-induced seizures and lethality in these lines may prove useful in elucidating the underlying mechanisms of these traits. In a subsequent study, the incidence of seizures in F1 and F2 generation mice from hybrid matings of LS and SS parents was not consistent with a single gene hypothesis, suggesting that multiple genes and receptors mediate seizurgenic responses to cocaine. Further, albino mice from the F2 generation did not show a significantly different incidence of seizures than non-albino mice, indicating that of the genes contributing to seizures following cocaine, none appear to be closely associated with the albino locus on mouse chromosome seven.