Founder Females Research Articles

Production of Recombinant Human Von Willebrand Factor in the Milk of Transgenic Pigs

Von Willebrand factor (vWF), a large multimeric glycoprotein present in blood plasma, is a blood protein of the coagulation system. It is defective in von Willebrand disease and is involved in a large number of other diseases, including thrombotic thrombocytopenic purpura-hemolytic uremic syndrome and heyde's syndrome. We have developed a line of transgenic swine harboring recombinant human von Willebrand factor (rhvWF) cDNA through microinjection of fertilized one-cell pig zygotes. Expression of rhvWF in the mammary gland and secretion of rhvWF into the milk of the transgenic swine were confirmed by immunohistochemical and western blot analyses, respectively, and rhvWF proteins were detected in milk from all lactating founder females at concentrations that were 28- to 56-folds greater than that in circulating human plasma. The amino acid sequence of rhvWF protein in the transgenic pig milk matched that of vWF produced from human blood plasma. This study provides evidence that production of rhvWF from transgenic pig milk is a potentially valuable technology and can be used as a cost-effective alternative in clinical applications.

Fertility control of rodent pests

Ricefield rats (Rattus argentiventer) in south-east Asian rice fields and house mice (Mus domesticus) in Australian grain fields are major pest species. They cause damage before and after harvest and carry zoonotic diseases. For both species, management techniques have been pursued using the approach of immunocontraceptive vaccination. We review results from a series of enclosure and field studies conducted with these species to assess the effects of fertility control in small rodents. In the experiments, fertility control was simulated by tubal ligation, ovariectomy or progesterone treatment. A once-off sterilisation of 50–75% of enclosed founder females considerably reduced reproductive output of ricefield rat populations until the end of the reproductive period. In house mice, similar success was achieved when a sterility level of 67% of female founders and offspring was maintained. Repeated antifertility treatments are required because of the much longer breeding period of house mice versus ricefield rats. Comparing the results of enclosure trials with the outcome of simulation models suggests that partial compensation of treatment effects can occur through enhanced reproduction of the remaining fertile females and improved survival of juveniles. However, such compensatory effects as well as behavioural consequences of sterility in field populations are not likely to prevent the management effect at the population level. The challenge for effective fertility control of small rodents in the field is the wide-scale delivery of an antifertility treatment to founders at the beginning of the breeding season and to fertile immigrants that are recruited into the population, which otherwise contribute to the reproductive output at the population level. Future research efforts should focus on species-specific techniques and on agents that can be effectively delivered via bait.

Home range size and overlap in female root voles: effects of season and density

In small mammals living in highly seasonal environments, observational studies show that female home range size and exclusiveness are smaller in the nonbreeding winter season than in the breeding summer season. This has led to the notion that nonbreeding females are more social and decrease territorial behavior during winter. However, because territoriality decreases with increasing population density, and density normally increases during the breeding season, the effects of density and season on social structure are usually confounded. To find out which of the 2 factors explains space use, we experimentally established 3 high-density and 3 low-density root vole (Microtus oeconomus) populations in late spring and monitored the populations into the nonbreeding winter season. Population sizes were controlled throughout the breeding period to minimize seasonal variation in density. Home range sizes were larger in founder females than in field-born females but did not change with season or density. Area exclusively used by individual females was lower in winter than summer, and founder females decreased exclusiveness as density increased. We argue that this seasonal pattern of space use might be caused by variation in benefits of group living, whereas founder females also responded to density-dependent competition by reducing area exclusively used. Key words: density, Microtus oeconomus, season, space use. [Behav Ecol]

231 HISTOCOMPATIBLE PARTHENOGENETIC EMBRYONIC STEM CELLS

Organ or tissue transplantation is the preferred treatment for numerous diseases but is hindered by immunologic barriers. Genetically matched pluripotent embryonic stem cells generated via nuclear transfer (ntES cells) or parthenogenesis (pES cells) are possible sources of histocompatible cells and tissues. We have developed two ways of isolating pES cells that carry the full complement of major histocompatibility complex (MHC) antigens of the oocyte donors. One method entails activation of oocytes after blockade of karyokinesis in meiosis II, followed by selection of predominantly homozygous pES cells that have undergone recombination in their MHC antigen region to restore the heterozygous maternal MHC genotype (parthenote recombinant, or prES cells). The second method involves activation of immature oocytes after blockade of karyokinesis of meiosis I, followed by selection of predominantly heterozygous pES lines that retain the MHC genotype of the oocyte donor (parthenote clone recombinant, or pcrES cells). The cells are pluripotent by several criteria: teratoma formation, in vitro differentiation into hematopoietic elements, and high-level skin chimerism in blastocyst chimeras. Breeding of 8 founder females and examination of over 700 progeny failed to demonstrate germ line transmission of the pES cells. Injection of over 50 tetraploid embryos with these lines and embryo transfer have failed to support full gestational development. However, differentiated tissues from these pluripotent ES cells engraft when transplanted into genetically matched immunocompetent recipients, demonstrating that selected pES cells can serve as a source of histocompatible tissues for transplantation.

Intra-family aggression and offspring expulsion in Mongolian gerbils ( Meriones unguiculatus) under restricted environments

Mongolian gerbils live in families consisting of a founder pair, to which reproduction is mainly restricted, and the offspring. They are described as cooperative breeder in which males and offspring act as helpers. Family dynamics have not been systematically investigated, particularly concerning the long-term consequences of periods of aggression. In a conceptual framework, promoting factors were investigated for the outbreak of aggression and its consequences on the families and on the individual level. Moreover, previously defined and described integrated (IFMs) and expelled family members (EFMs) were further characterized by frequent measurements of body mass and body composition. Six families were monitored for at least 1.5 years under controlled laboratory conditions. Regularly, the family composition and the individual state of each family member were inspected. In case of agonistic interactions, aggression periods were characterized by onset, number, duration, number of expelled animals and family size. First aggression period has been occurred 247.8±37.7 days post-founding. As a consequence, family size was reduced significantly from 18.7±1.8 to 17.5±1.8 animals; the number of females decreased too from 10.6±1.8 to 9.7±1.8 females per family. All Mongolian gerbils experienced 2.4±0.2 aggression periods per life. All EFMs had a reduced body mass increase during aggression periods compared with integrated ones. Expelled males had a lower body mass than their integrated siblings; there was no such difference in females. In each aggression period, 2.6±0.2 adult animals per family were expelled. There was no sex-specific expulsion rate. Mainly founder females acted as aggressors (in 60% of all aggression periods). Up to three animals operated together aggressively, but mainly only one animal attacked the other family members (in 78% of all aggression periods). To conclude, animals of both sexes were excluded due to changes in family structure and an increased family size. Furthermore, females were expelled due to competition for exclusive reproduction. Males with lower body mass were more prone to be expelled, whereas in females no morphometrical characteristics favour the expulsion.

THE IMPACT OF STERILIZED FEMALES ON ENCLOSED POPULATIONS OF RICEFIELD RATS

For the sustainable management of small mammals, fertility control may be used in the future. Little is known about what proportions of females need to be sterilized to achieve an impact on population size and what compensatory processes may act on the population level. We tested the impact of surgical sterilization of zero, 25, 50, and 75% of females on the population dynamics and demography of enclosed populations of ricefield rats (Rattus argentiventer) and damage to rice crop. Sterilizing 50% of female founders (6 of 12) decreased population size at the end of the breeding season by about 50%. We used a simulation model, based on the breeding biology of the ricefield rat in the field and in the control enclosures, to generate the expected dynamics of the enclosure populations. The results suggested that compensation occurred in the enclosures where 75% of female founders (9 of 12) had been sterilized. We detected a slight tendency for 50% higher numbers of recent uterine scars in fertile founder females in the 50% and 75% treatments versus 25% treatments and controls (P = 0.198). The primary demographic mechanism for compensation was higher survival of young rats in enclosures where 75% of females were sterilized. However, compensation only partially offset the decrease in population size. We found no conclusive evidence that the reproductive output of F1 generation females was higher when large proportions of female founders were sterilized. Early in the breeding season, the per capita damage to rice plants in populations without sterilized ricefield rats was increased. Our results suggest that the sterilization of >50% of females in ricefield rat populations can reduce rat population growth and rat damage to rice crops.

Development and initial characterization of xenomitochondrial mice.

Xenomitochondrial mice harboring trans-species mitochondria on a Mus musculus domesticus (MD) nuclear background were produced. We created xenomitochondrial ES cell cybrids by fusing Mus spretus (MS), Mus caroli (MC), Mus dunni (Mdu), or Mus pahari (MP) mitochondrial donor cytoplasts and rhodamine 6-G treated CC9.3.1 or PC4 ES cells. The selected donor backgrounds reflected increasing evolutionary divergence from MD mice and the resultant mitochondrial-nuclear mismatch targeted a graded respiratory chain defect. Homoplasmic (MS, MC, Mdu, and MP) and heteroplasmic (MC) cell lines were injected into MD ova, and liveborn chimeric mice were obtained (MS/MD 18 of 87, MC/MD 6 of 46, Mdu/MD 31 of 140, and MP/MD l of 9 founder chimeras, respectively). Seven MS/MD, 1 MC/MD, and 11 Mdu/MD chimeric founder females were mated with wild-type MD males, and 18 of 19 (95%) were fertile. Of fertile females, only one chimeric MS/MD (1% coat color chimerism) and four chimeric Mdu/MD females (80-90% coat color chimerism) produced homoplasmic offspring with low efficiency (7 of 135; 5%). Four male and three female offspring were homoplasmic for the introduced mitochondrial backgrounds. Three male and one female offspring proved viable. Generation of mouse lines using additional female ES cell lineages is underway. We hypothesize that these mice, when crossbred with neurodegenerative-disease mouse models, will show accelerated age-related neuronal loss, because of their suboptimal capacity for oxidative phosphorylation and putatively increased oxidative stress.

Social categories in families of Mongolian gerbils

Mongolian gerbils are a species of rodent in Asia living in families, although aggression occurs within these social units. The aim of this study was to determine the causes for the surge of intrafamily aggression and to characterize different types of animals. Due to behavioral measures, animals were assigned to distinct social categories and the consequences of social stress were analyzed on an individual level. Four families established from founder pairs were kept for up to 2.5 years in large enclosures. Social interactions within each family were recorded for at least 5 days per week throughout the long-term experiment and fecal samples were collected weekly for the determination of corticosterone concentration. Moreover, adrenals were weighed and histologically analyzed. Two main causes for the outbreak of aggression were distinguished: changes in family structure and female competition for reproduction. As a result of these aggression periods, it was possible to divide animals into social categories: (1) integrated family members (IFM), (2) founder pair animals (FPA) and (3) expelled family members (EFM). Integrated animals had the lightest adrenal glands [related to the fat-free mass (FFM)] and lowest corticosterone level in aggression periods. Founder animals were never attacked by other members, reproduced successfully and displayed the highest stress level in most of the measured parameters. EFM were attacked and excluded mainly by the founder females. Their stress level was intermediate.

Effect of Temperature on Rearing of the First Brood by the Founder Females of the Ant Lasius niger (Hymenoptera, Formicidae) : Latitude-Dependent Variability of the Response Norm

It has been established that duration of brood development and success of rearing of the first worker individuals by founder females of the ant Lasius niger from the northern population (St. Petersburg) depend on temperature conditions to a larger extent than of individuals from the southern areal (Borisovka Village, Belgorod Region) The development rate of individuals from the northern population is lower as compared with individuals from the southern population in the low temperature range (17–20°C), but is higher at elevated temperatures (22–27°C). This leads to a greater slope of the temperature regression line of the development rate on the temperature, to lower values of the sum of effective temperatures, and to a higher temperature threshold of development in the northern population. Lower temperatures have a stronger effect on development of larvae from the northern population by inducing diapause in the greater number of individuals as compared with larvae from the southern population. The L. niger founder females require, on average, higher temperatures than the females from the southern populations of this species for rearing the first worker ants during the same summer season (i.e., without winter diapause). Thus, ants of the southern populations, when rearing the first brood, use a strategy of faster development at higher temperatures, while low temperatures restrict to the greater extent the development of their brood as compared with ants from the southern populations. It is concluded that one of the ways of physiological adaptation of ants for inhabitance on the North is such change of the norm of response to temperature, at which development becomes more temperature-dependent, the physiological response to higher temperatures increasing at the cost of its decrease at lower temperatures.

Distribution of CGG repeat sizes within the fragile X mental retardation 1 (FMR1) homologue in a non-human primate population.

Fragile X syndrome, the most common inherited form of mental retardation, arises in individuals with more than 200 CGG repeats in the 5' untranslated region of the fragile X mental retardation 1 ( FMR1) gene. Although CGG repeat numbers comparable to those found in the normal human population are found in various non-human primates, neither the within-species size variation nor the propensity for expansion of the CGG repeat has been described for any non-human primate species. The allele distribution has now been determined for FMR1 (homologue) CGG repeats of 265 unrelated founder females of Macaca mulatta monkeys. Among 530 X chromosomes, at least 26 distinct repeat lengths were identified, ranging from 16 to 54 CGG repeats. Of these alleles 79% have between 25 and 33 CGG repeats. Detailed examination of the CGG region revealed a conserved G (CGG)(2 )G interruption, although in no case was an AGG trinucleotide detected. Two animals carried borderline premutation alleles with 54 CGG repeats, within the region of marginal instability for humans. Thus, M. mulatta may be useful as an animal model for the study of fragile X syndrome.

Effects of refuge availability on the population dynamics of Triatoma infestans in central Argentina

Summary As part of research on the control and mathematical modelling of transmission of Chagas disease, we tested the joint effects of refuge quantity and quality on the population dynamics of Triatoma infestans in 12 experimental huts under natural climatic conditions in central Argentina. The 2‐year trial involved three types of huts that mimicked rural houses, with a gradient of refuges determined by the type of thatched roof and whether the walls were plastered or not. Each treatment comprised three replicate huts and one control hut, each of which was a closed population that housed a chicken at night and was colonized with five virgin female and three male T. infestans in mid‐summer. The replicate huts were dismantled monthly to count the number of live and dead T. infestans by stage and to mark the emerged insects. Control huts were dismantled only at the end of the first and second year to count the bugs. The mean abundance of live T. infestans was significantly greater in huts with maximum (final mean 1834; range 337–3630 bugs) rather than intermediate (final mean 383; range 71–692 bugs) or minimum refuges (final mean 103; range 0–103 bugs). The bug populations under minimum refuges returned to baseline levels at 1 year post‐colonization and two populations went extinct. Apparent female fecundity was affected significantly by refuge availability and time. Survival of the founder females until 1 year post‐colonization successively decreased from 20% to 7% and 0% in huts ranging from maximum to minimum refuges. The basic reproduction number Ro steadily decreased from 3·91 to 2·36–0·25 bugs per female bug in maximum to minimum refuge huts, respectively. Synthesis and applications. Population persistence, growth rate and the maximum number of T. infestans that a hut may support depend on the physical structure for a fixed number of chickens, in agreement with the available experimental and field evidence. Environmental management measures, such as plastering of walls and wire‐fencing corrals, aimed at reducing the availability of refuges and oviposition sites may exert a strong adverse impact on the population dynamics of T. infestans.

Inbreeding depression in fecundity and inbred line extinction in the bulb mite, Rhizoglyphus robini.

This study investigated the magnitude of inbreeding depression in fecundity, and whether the depression is purged during six generations of sib mating in the bulb mite, Rhizoglyphus robini. The progeny resulting from a single generation of brother-sister mating suffered significant inbreeding depression in fecundity. During the following six generations of continuous sib-mating, 58% lines were lost, 45% because of sterility and 13% because of preadult mortality. The lines were then outcrossed, and their inbreeding depression compared with that of the base population. The inbreeding depression for the outcrossed population was 0.15, and for the base population 0.19, but the difference was not significant. The lack of significant purging of inbreeding depression indicates that it was caused either by detrimental genes of small effect, or by the breaking down of overdominant relations between alleles. However, the large proportion of extinct lines points to the former mechanism as a predominant cause of inbreeding depression. Theory predicts that the probability of line extinction with inbreeding increases with its load of mutations. If phenotypic variation in fecundity was partly because of differences in numbers of mutations carried by individuals, the fecundity of the line founder could be expected to correlate with the probability that the line derived from it will survive long-term inbreeding. Indeed, fecundity of founder females was significantly associated with line survival, which suggests that line extinction rate may be used as a method to study individual mutational loads, for example, in studies of sexual selection.

Genetic Structure of <I>Aedes albopictus</I> (Diptera: Culicidae) Populations Based on Mitochondrial ND5 Sequences: Evidence for an Independent Invasion into Brazil and United States

Aedes albopictus (Skuse), Asian tiger mosquito, a dengue fever vector, colonized the United States and Brazil ≈15 yr ago. The geographic origin and changes in population structure were examined using DNA sequences of mitochondrial NADH dehydrogenase subunit 5 (ND5). A 450 bp region was amplified by polymerase chain reaction (PCR) and screened for variation by both the single strand conformation polymorphism (SSCP) mutation detection technique and direct sequencing. The United States populations were typified by some local differentiation, but the most common and widespread haplotype was characteristic of the native range (Asian) populations as well. A comparison of the native range populations with the United States populations indicated a shared ancestral origin. The Brazil populations contained private (population specific) haplotypes, indicating no genetic exchange between the Brazil and the United States populations since introduction. Local differentiation was not observed among Brazil populations in contrast to the United States populations; this suggested distinctive dispersal mechanisms in the two countries. Extremely low variability was present in the A. albopictus mitochondrial sequences when contrasted with other taxa, reflecting a history of dispersal from a narrow genetic base. In contrast, relatively high levels of variation in several sequenced nuclear loci indicated the following colonization sequence: (1) the founding population was small, genetic drift had insufficient time to reduce variation at nuclear loci, and (2) populations successively expanded to new geographic areas established from a few founder females.

Microsatellite diversity, pedigree relatedness and the contributions of founder lineages to thoroughbred horses.

The thoroughbred (TB) horse is one of the oldest breeds of domestic animals, with pedigree records spanning three centuries. Because the population is essentially closed, there is concern about loss of genetic variation. Here we report two parallel analyses. In the first, genetic variation in the current population is measured using data from 13 microsatellite loci in 211 horses with relationships calculated based on allele sharing. In the second analysis, pedigree information is used to calculate genetic relationships between animals based on shared ancestry. These two measures of relationship are compared and shown to be closely related. Together, they provide an estimate of the amount of genetic variation which existed in founder animals. This study confirms the narrow genetic base of the breed and provides comprehensive analysis of contributions of founder animals. Seventy-eight percent of alleles in the current population are derived from 30 founders, 27 of these male. Ten founder females account for 72% of maternal lineages, while one founder stallion is responsible for 95% of paternal lineages.

Complete Replacement of the Mitochondrial Genotype in a Bos indicus Calf Reconstructed by Nuclear Transfer to a Bos taurus Oocyte

Due to the exclusively maternal inheritance of mitochondria, mitochondrial genotypes can be coupled to a particular nuclear genotype by continuous mating of founder females and their female offspring to males of the desired nuclear genotype. However, backcrossing is a gradual procedure that, apart from being lengthy, cannot ascertain that genetic and epigenetic changes will modify the original nuclear genotype. Animal cloning by nuclear transfer using host ooplasm carrying polymorphic mitochondrial genomes allows, among other biotechnology applications, the coupling of nuclear and mitochondrial genotypes of diverse origin within a single generation. Previous attempts to use Bos taurus oocytes as hosts to transfer nuclei from unrelated species led to the development to the blastocyst stage but none supported gestation to term. Our aim in this study was to determine whether B. taurus oocytes support development of nuclei from the closely related B. indicus cattle and to examine the fate of their mitochondrial genotypes throughout development. We show that indicus:taurus reconstructed oocytes develop to the blastocyst stage and produce live offspring after transfer to surrogate cows. We also demonstrate that, in reconstructed embryos, donor cell-derived mitochondria undergo a stringent genetic drift during early development leading, in most cases, to a reduction or complete elimination of B. indicus mtDNA. These results demonstrate that cross-subspecies animal cloning is a viable approach both for matching diverse nuclear and cytoplasmic genes to create novel breeds of cattle and for rescuing closely related endangered cattle.

Cytochrome b gene haplotypes characterize chromosomal lineages of anoa, the Sulawesi dwarf buffalo (Bovidae: Bubalus sp.).

Partial mitochondrial cytochrome b gene sequences reveal two deeply differentiated mtDNA lineages in anoa dwarf buffaloes (Bubalus depressicornis) from the studbook herd in European zoos. Three matrilinear lineages of lowland anoas (depressicornis type) contributed three rather similar sequence haplotypes, but one remarkably distinct haplotype was observed exclusively in mountain anoas (quarlesi type) descended from one founder female. The carriers of the distinctive mtDNA haplotype were also distinguished by several chromosomal and phenotypic peculiarities too. The differentiation between the mtDNA lineages of anoa approached or even surpassed the genetic divergence between some uncontested species of wild cattle. The depth of this haplotype divergence in anoas is discussed against the background of the phylogenetic age of these paleoendemic inhabitants of a predator-free island refugium, Sulawesi, who are among the most plesiomorphic living bovines. The studbook breeding of captive anoas as a safeguard against extinction might profit from such population genetic markers. These cytochrome b gene sequences were unable to resolve the phylogeny of nine bovine taxa robustly, except the divergence of Bubalus, Synceros, Bison, and Bos (sensu lato) genera.

A canine model of familial mammary gland neoplasia.

Intact female Beagles from life-span studies in the Lovelace Respiratory Research Institute colony were examined for mammary tumor incidence. The breeding colony, founded in 1963, produced five generations from 28 founder females. After proportional hazards analysis, two maternal families were shown to have markedly different phenotypes, one susceptible and one resistant to mammary neoplasia, as compared with the entire colony. When tumors were subdivided into benign and malignant based on local invasiveness, familial differences in tumor incidence were preserved for each tumor type. Fifty-seven females in the susceptible family developed 149 benign and 39 malignant tumors, and 95 females in the resistant family developed 70 benign and 20 malignant tumors. The ratio of benign to malignant tumors of about 4:1 for both families was higher than expected. Using Kaplan-Meier and log-rank analyses, the susceptible family had a 50% malignant tumor incidence by age 13.6 years, whereas the resistant family did not have a 50% incidence until 17.0 years (P = 0.0065). Because of marked censoring, Kaplan-Meier analyses could not provide an estimate of the 50% benign tumor incidence; mean incidence age was calculated instead. These estimates for benign tumors for susceptible and resistant families were 10.8 and 13.8 years (P = 0.0001), respectively. Using chi(2) tests, families had no differences in the occurrence of the types of benign (P = 0.098) or malignant (P = 0.194) tumors or in the ratio of benign to malignant tumors (P = 0.778). Immunohistochemical analysis of malignant tumors from both families did not demonstrate differences in p53 mutation rate or p185erbB-2 expression. These results suggest that 1) genetic factors produce familial differences in the age of onset of both benign and malignant mammary tumors; histologic types do not segregate by family; 2) the ratio of benign to malignant tumors is greater than formerly reported; and 3) neither p53 nor p185erbB-2 alterations are the basis for the familial predisposition.

Matrilineal kin clusters and their effect on reproductive success in the field vole Microtus agrestis

Kin clusters of philopatric females are thought to form the basic social organization of breeding females in various vole species. The spatial association between young breeding females and their mothers was studied in five 2500-m* enclosures in natural habitats during midand late breeding season in summer 1992. The mothers (founder females) were introduced into the enclosures in die beginning of the study in June, whereas the young breeding females were born within the enclosures. Matrilineal kinship was determined by using radionudides. In July-August, 58% of young breeding females were philopatric, but 82% of the mother-daughter associations broke up until August-September. Of the young females that started to breed in August-September, only 12% were philopatric Thus the kin clusters found were short Hved and few in number during the late breeding season. The reduction in the incidence of the kin clusters coincided with an increase of population density. The mean reproductive success of females breeding in kin clusters was better than that of those breeding separately. In addition, among the nonphilopatric females there was a positive, significant correlation between reproductive success and the distance to the nearest unrelated founder female. Such correlation was not found among the philopatric females.

An early and massive wave of germinal cell apoptosis is required for the development of functional spermatogenesis.

Transgenic mice expressing high levels of the BclxL or Bcl2 proteins in the male germinal cells show a highly abnormal adult spermatogenesis accompanied by sterility. This appears to result from the prevention of an early and massive wave of apoptosis in the testis, which occurs among germinal cells during the first round of spermatogenesis. In contrast, sporadic apoptosis among spermatogonia, which occurs in normal adult testis, is not prevented in adult transgenic mice. The physiological early apoptotic wave in the testis is coincident, in timing and localization, with a temporary high expression of the apoptosis-promoting protein Bax, which disappears at sexual maturity. The critical role played by the intracellular balance, probably hormonally controlled, of the BclxL and Bax proteins (Bcl2 is apparently not expressed in normal mouse testis) in this early apoptotic wave is shown by the occurrence of a comparable testicular syndrome in mice defective in the bax gene. The apoptotic wave appears necessary for normal mature spermatogenesis to develop, probably because it maintains a critical cell number ratio between some germinal cell stages and Sertoli cells, whose normal functions and differentiation involve an elaborate network of communication.

Relationships Between Polymorphism for Mitochondrial Deoxyribonucleic Acid and Yield Traits of Holstein Cows

Two independent data files from the breeding herd of Iowa State University and six North Carolina herds were used to examine relationships between yield traits and mtDNA polymorphism. Maternal lineages were established by tracing ancestry of cows to founder females in the herd book of the Holstein Association. Data from Iowa State University were 1476 records from 602 cows from 29 maternal lineages. The nucleotides of mtDNA encoding rRNA were sequenced. Eleven sites of polymorphism were found. An animal model for gene substitution was used to examine the relationship between sequence differences and yield traits. Traits analyzed were mature equivalent yield of milk, fat, SNF, and milk energy as well as concentrations of fat, SNF, and milk energy. Effects of sequence differences were significant for most traits. Sequence information from the D-loop was available for 12 lineages from North Carolina. The effect of polymorphism at 4 sites was examined using 1472 records from 668 cows. Traits measured were the same, except that protein replaced SNF. No significant relationships existed between any of the traits and D-loop polymorphism, but results suggested that an association might exist between polymorphism and concentrations of milk yield, fat percentage, and energy. Whenever a significant relationship was detected, the effect of mutation (rare genotype) was detrimental.