Distribution and effects of the 1/29 Robertsonian translocation in cattle

A working model for the formation of Robertsonian chromosomes

Robertsonian chromosomes form by fusion of two chromosomes that have centromeres located near their ends, known as acrocentric or telocentric chromosomes. This fusion creates a new metacentric chromosome and is a major mechanism of karyotype evolution and speciation. Robertsonian chromosomes are common in nature and were first described in grasshoppers by the zoologist W. R. B. Robertson more than 100 years ago. They have since been observed in many species, including catfish, sheep, butterflies, bats, bovids, rodents and humans, and are the most common chromosomal change in mammals. Robertsonian translocations are particularly rampant in the house mouse, Mus musculus domesticus, where they exhibit meiotic drive and create reproductive isolation. Recent progress has been made in understanding how Robertsonian chromosomes form in the human genome, highlighting some of the fundamental principles of how and why these types of fusion events occur so frequently. Consequences of these fusions include infertility and Down's syndrome. In this Hypothesis, I postulate that the conditions that allow these fusions to form are threefold: (1) sequence homology on non-homologous chromosomes, often in the form of repetitive DNA; (2) recombination initiation during meiosis; and (3) physical proximity of the homologous sequences in three-dimensional space. This Hypothesis highlights the latest progress in understanding human Robertsonian translocations within the context of the broader literature on Robertsonian chromosomes.

Chromosome Changes in Soma and Germ Line: Heritability and Evolutionary Outcome

The origin and inheritance of chromosome changes provide the essential foundation for natural selection and evolution. The evolutionary fate of chromosome changes depends on the place and time of their emergence and is controlled by checkpoints in mitosis and meiosis. Estimating whether the altered genome can be passed to subsequent generations should be central when we consider a particular genome rearrangement. Through comparative analysis of chromosome rearrangements in soma and germ line, the potential impact of macromutations such as chromothripsis or chromoplexy appears to be fascinating. What happens with chromosomes during the early development, and which alterations lead to mosaicism are other poorly studied but undoubtedly essential issues. The evolutionary impact can be gained most effectively through chromosome rearrangements arising in male meiosis I and in female meiosis II, which are the last divisions following fertilization. The diversity of genome organization has unique features in distinct animals; the chromosome changes, their internal relations, and some factors safeguarding genome maintenance in generations under natural selection were considered for mammals.

The effect of the Robertsonian translocation 1/29 on the fertility of beef cattle reared under extensive conditions: a 30 years retrospective study

The Robertsonian translocation 1/29 (rob(1;29)) is the most worldwide widespread chromosomal abnormality in domestic animals. Previous studies have demonstrated its negative effect on fertility in dairy herds, but not in beef cattle extensively bred. In this study, we analyzed the effect of rob(1;29) in a Retinta cattle breed dataset gathered during the last 30 years. The data presented herein includes rob(1;29) analysis of 11,505 cows from 251 herds, pedigree information of 24,790 animals, and 67,457 calving records. Fertility was evaluated using estimated breeding values for the reproductive efficiency (Re), calculated as the percentage ratio between the number of calvings of an individual with the number expected in an optimal situation. Our results showed that cows carrying the heterozygote genotype showed a significant decrease in their Re (-5.10%, p<0.001). No decrease was detected in free rob(1;29) animals and homozygous carriers. In addition, the incidence of rob(1;29) in the breed fertility was decreased to very low values after 30 years of avoiding selection bulls carrier as stallions. The effect of rob(1;29) in cattle fertility is only significant when the prevalence of carrier individuals is high. Selecting against the disease only by the paternal side reduced the incidence to negligible values.

Sperm chromosome segregation of rob(4;16) and rob(4;16)inv(4) in the brown brocket deer (Mazama gouazoubira)

The genus Mazama stands out among the Neotropical deer due to their wide intra and interspecific karyotypic diversification, which is associated with an accentuated chromosomal fragility. There are reports of heterozygous Robertsonian translocation (RT) carriers in a free-range population of Mazama gouazoubira (brown brocket deer), as well as in captive animals of this and other species of the genus. To analyze possible negative impacts of heterozygous chromosome rearrangements on reproductive fitness of the carriers, we performed an analysis of sperm meiotic segregation in four brown brocket bucks, carriers of a rob(4;16), and compared the results with those of a normal buck. We established a reliable FISH and sperm-FISH protocol for the brown brocket deer using bovine (Bos taurus; diploid number, 2n = 60) whole chromosome painting (WCP) and BAC probes. Using BAC probes, we revealed the presence of a paracentric inversion (PAI) of the fused chromosome 4 in two of the four analyzed RT carriers. The mean frequency of normal/balanced sperm in the translocation carriers was significantly lower than in the normal buck (94.78% vs 98.40%). The mean value of total unbalanced spermatozoa was almost doubled in the RT/PAI carriers (6.68%) when compared to RT carriers (3.76%), but the difference was not statistically significant. This study demonstrated the efficiency of FISH with bovine WCP and BAC probes in the characterization of chromosome rearrangements and gametic segregation patterns in brown brocket deer. Our results indicate a low to moderate increase in the rates of unbalanced meiotic segregation products in brown brocket bucks heterozygous for RT and RT/PAIs.

Symposium review: Advances in sequencing technology herald a new frontier in cattle genomics and genome-enabled selection

The cattle reference genome assembly has underpinned major innovations in beef and dairy genetics through genome-enabled selection, including removal of deleterious recessive variants and selection for favorable alleles affecting quantitative production traits. The initial reference assemblies, up to and including UMD3.1 and Btau4.1, were based on a combination of clone-by-clone sequencing of bacterial artificial chromosome clones generated from blood DNA of a Hereford bull and whole-genome shotgun sequencing of blood DNA from his inbred daughter/granddaughter named L1 Dominette 01449 (Dominette). The approach introduced assembly gaps, misassemblies, and errors, and it limited the ability to assemble regions that undergo rearrangement in blood cells, such as immune gene clusters. Nonetheless, the reference supported the creation of genotyping tools and provided a basis for many studies of gene expression. Recently, long-read sequencing technologies have emerged that facilitated a re-assembly of the reference genome, using lung tissue from Dominette to resolve many of the problems and providing a bridge to place historical studies in common context. The new reference, ARS-UCD1.2, successfully assembled germline immune gene clusters and improved overall continuity (i.e., reduction of gaps and inversions) by over 250-fold. This reference properly places nearly all of the legacy genetic markers used for over a decade in the industry. In this review, we discuss the improvements made to the cattle reference; remaining issues present in the assembly; tools developed to support genome-based studies in beef and dairy cattle; and the emergence of newer genome assembly methods that are producing even higher-quality assemblies for other breeds of cattle at a fraction of the cost. The new frontier for cattle genomics research will likely include a transition from the individual Hereford reference genome, to a "pan-genome" reference, representing all the DNA segments existing in commonly used cattle breeds, bringing the cattle reference into line with the current direction of human genome research.

Persistent Mullerian duct Syndrome in a Brazilian miniature schnauzer dog

Here we describe an eight-year-old miniature schnauzer (MS) dog from Brazil with Persistent Mullerian Duct Syndrome (PMDS) and the single base pair substitution in AMHR2 exon 3, first detected in this breed in the USA. This finding is evidence of mutation dissemination to South America. In PMDS, a type of XY Disorder of Sex Development (DSD), dogs with a male karyotype and external phenotype also have a uterus, oviducts, and a cranial vagina internally. Approximately half of PMDS MS are unilaterally or bilaterally cryptorchid and many develop pyometra and/or Sertoli cell tumor. Bilateral Sertoli cell testicular tumors were present in this case, and the dog died a few days after surgical castration and hysterectomy. Although the karyotype was compatible with male chromosomal sex, a Robertsonian translocation was also identified, which may be an incidental finding. This report emphasizes the importance of cytogenetic and molecular genetic analyses, along with clinical examination, to identify chromosomal or genetic variations associated with canine PMDS. These are helpful tools to obtain early diagnosis in the MS, which is important to improve health outcomes for affected dogs and to reduce the prevalence of PMDS and cryptorchidism in this breed by avoiding the mating of carriers.

Pregnancy losses in cattle: potential for improvement

For heifers, beef and moderate-yielding dairy cows, it appears that the fertilisation rate generally lies between 90% and 100%. For high-producing dairy cows, there is a less substantive body of literature, but it would appear that the fertilisation rate is somewhat lower and possibly more variable. In cattle, the major component of embryo loss occurs in the first 16 days following breeding (Day 0), with emerging evidence of greater losses before Day 8 in high-producing dairy cows. In cattle, late embryo mortality causes serious economic losses because it is often recognised too late to rebreed females. Systemic concentrations of progesterone during both the cycle preceding and following insemination affect embryo survival, with evidence of either excessive or insufficient concentrations being negatively associated with survival rate. The application of direct progesterone supplementation or treatments to increase endogenous output of progesterone to increase embryo survival cannot be recommended at this time. Energy balance and dry matter intake during the first 4 weeks after calving are critically important in determining pregnancies per AI when cows are inseminated at 70-100 days after calving. Level of concentrate supplementation of cows at pasture during the breeding period has minimal effects on conception rates, although sudden reductions in dietary intake should be avoided. For all systems of milk production, more balanced breeding strategies with greater emphasis on fertility and feed intake and/or energy must be developed. There is genetic variability within the Holstein breed for fertility traits, which can be exploited. Genomic technology will not only provide scientists with an improved understanding of the underlying biological processes involved in fertilisation and the establishment of pregnancy, but also, in the future, could identify genes responsible for improved embryo survival. Such information could be incorporated into breeding objectives in order to increase the rate of genetic progress for embryo survival. In addition, there is a range of easily adoptable management factors, under producer control, that can either directly increase embryo survival or ameliorate the consequences of low embryo survival rates. The correction of minor deficits in several areas can have a substantial cumulative positive effect on herd reproductive performance.

Embryo death in cattle: an update

For heifers, beef and moderate-yielding dairy cows, fertilisation generally exceeds 90%. In high-producing dairy cows, it may be lower and possibly more variable. The major component of embryo loss occurs before Day 16 following breeding, with emerging evidence of greater losses before Day 8 in high-producing dairy cows. Late embryo loss causes serious economic losses because it is often recognised too late to rebreed females. Systemic concentrations of progesterone during the cycles both preceding and following insemination affect embryo survival; too-high or too-low a concentration has been shown to be negatively associated with survival rate. Energy balance and dry matter intake during the 4 weeks after calving are critically important in determining conception rate when cows are inseminated 70 to 100 days after calving. More balanced breeding strategies with greater emphasis on fertility, feed intake and energy must be developed. Genetic variability for fertility traits can be exploited; genomic technology will not only provide scientists with an improved understanding of the underlying biological processes involved in fertilisation and the establishment of pregnancy, but could identify genes responsible for improved embryo survival. Their incorporation into breeding objectives would increase the rate of genetic progress for embryo survival. There is a range of easily adoptable management factors, under producer control, that can either directly increase embryo survival or ameliorate the consequences of low embryo survival rates. The correction of minor deficits in several areas can have a substantial overall effect on herd reproductive performance.

Karyotype of Malayan Gaur (Bos gaurus hubbacki), Sahiwal-Friesian cattle and Gaur x cattle hybrid backcrosses

Interspecific hybridization has been reported for a wide variety of vertebrate species either spontaneous or by organized crossing of bovine species. The hybrids were often carrying intermediate characters genetically and phenotypically of the parents. Thus, status information of both aspects is valuable in animal production for selection and breeding management. The Gaur-cattle hybrids was reported to be superior in production value compared to their parent cattle but fertility status was still questionable. The project was abandoned due to their fertility issue and the hybrids were kept within the cattle in a dairy farm. Cytogenetic status and breeding record of the remaining herd were unavailable since then. The herd was then translocated to a deer farm (PTH Lenggong) and kept freely in the paddock. Recently, two female calves were born via inter se mating. Peripheral blood cultures of Malayan Gaur, Sahiwal-Friesian cattle and Gaur x cattle hybrid backcrosses were analyzed via Giemsa stained metaphase. The Gaur and cattle were having diploid chromosome number (2n) of 56 and 60, respectively. Interestingly, the backcrosses from the hybrids by cattle bulls were found to have two chromosome arrangements, which are 2n = 58 and 2n = 60.

Embryonic and early foetal losses in cattle and other ruminants

Embryo survival is a major factor affecting production and economic efficiency in all systems of ruminant milk and meat production. For heifers, beef and moderate yielding dairy cows, does and camelids it appears that fertilization generally lies between 90% and 100%. In high-producing dairy cows there is a less substantive body of literature, but it would appear that it is somewhat lower and perhaps more variable. In cattle, the major component of embryo loss occurs before day 16 following breeding with some evidence of greater losses before day 8 in high-producing dairy cows. In cattle late embryo loss, while numerically much smaller than early embryo mortality loss, nevertheless, causes serious economic losses to producers because it is often too late to rebreed females when they repeat. In multiple ovulating small ruminants, the loss rate is positively related to ovulation rate. Systemic concentrations of progesterone, during both the cycle preceding and following insemination, affect embryo survival rate with evidence that too high or indeed too low a concentration being negatively associated with survival rate. Uterine expression of mRNA for progesterone receptor, oestradiol receptor and retinol-binding protein appears to be sensitive to changes in peripheral concentrations of progesterone during the first week after artificial insemination. Energy balance and dry matter intake during 4 weeks after calving are critically important in determining conception rate when cows are inseminated at 70-100 days post-calving. Concentrate supplementation of cows at pasture during the breeding period has minimal effects on conception rates though sudden reductions in dietary intake should be avoided. For all systems of milk production, more balanced breeding strategies with greater emphasis on fertility and feed intake and/or energy balance must be developed. There is sufficient genetic variability within the Holstein breed for fertility traits. Alternative dairy breeds such as the Jersey or Norwegian Red could also be utilized. Genomic technology will not only provide scientists with an improved understanding of the underlying biological processes involved in fertilization and the establishment of pregnancy, but also, in the future, identify genes responsible for improved embryo survival. Its incorporation into breeding objectives would increase the rate of genetic progress for embryo survival.

A cattle breed close to 58 diploid number due to high frequency of rob(1;29)

Barrosa cattle, reared in the north of Portugal primarily for meat production, number about 40,000 (about 6% of all cattle in Portugal). Their fertility (number of calves per 100 cows) varies from 60% to 80% and is lower than that of other Portuguese cattle breeds. 195 animals (28 males and 167 females), randomly selected from a large area, were sampled for cytogenetical investigation. The results were the following: (a) 68 (34.9%) animals (7 males and 61 females) had normal karyotypes; (b) 127 (65.1%) were found to be carriers of rob(1; 29), as shown by G- and R-banding; (c) 102 (52.3%) animals (17 (8.7%) males and 85 (43.6%) females) were heterozygous carriers; (d) 25 (12.8%) animals (4 (2%) males and 21 (10.8%) females) were homozygous carriers. C-banding patterns revealed one block of constitutive heterochromatin (HC) in the proximal q-arm region of the translocated chromosome.

New Robertsonian translocation chromosomes in captive Thai gaur (Bos gaurus readei)

Robertsonian translocation have been well documented in domestic cattle, with the most commonly occurring fusion involving chromosomes 1 and 29. The widespread nature of this translocation is indicative of its ancient origin. Fifty Giemsa's stained metaphase spreads derived from lymphocyte cultures of the Thai gaur were analyzed for each animal. The Thai gaur had diploid chromosome number of 2n = 57 in male and 2n = 56 in female instead of the normal 2n = 58. The 2n = 57 in male chromosomes presence of an extra submetacentric chromosome and loss of two acrocentric chromosomes was observed [XY, 57, rob (1;29)]. The 2n = 56 in female chromosomes presence of two extra submetacentric chromosomes and loss of four acrocentric chromosomes was observed [XX, 56, rob (1;29)]. Results from the Giemsa's stained analyses confirm that the two autosomes (2n = 57) and four autosomes (2n = 56) involved in the translocation are the bovine homologues 1 and 29.

Evaluation of genotoxic effects of fumagillin by cytogenetic tests in vivo

Fumagillin is a naturally secreted antibiotic of the fungus Aspergillus fumigatus. It is used in veterinary medicine against microsporidiosis of bees and fish. In this study, the genotoxicity of fumagillin (in the form of fumagillin dicyclohexylamine) was evaluated in mouse bone-marrow cells using the mitotic index (MI), the chromosome aberration (CA) assay, and the micronucleus (MN) test. Fumagillin was administered to BALB/c mice by gavage, at doses of 25, 50, 75 mg/kg body weight (bw), repeated for 7 days at 24-h intervals, with water-sugar syrup as a negative control and cyclophosphamide (40 mg/kg bw) as a positive control. All experimental doses of fumagillin induced a significant decrease (p<0.001) in MI (3.47+/-0.04%, 3.17+/-0.01%, and 2.27+/-0.02%, respectively) in comparison with the negative control (6.00+/-0.01%). Fumagillin significantly (p<0.001) increased the frequency of MN (4.98+/-0.35, 8.45+/-0.57, and 12.02+/-0.37, respectively) over negative control (1.04+/-0.28). Significantly increased frequencies (p<0.01 or p<0.001) of numerical chromosomal aberrations (aneuploidies and polyploidies) and structural chromosomal aberrations such as gaps, breaks, and centric rings were observed at the highest experimental dose of fumagillin (75 mg/kg bw) compared with the negative control. However, with respect to the induction of Robertsonian translocations, both the intermediate (50 mg/kg bw) and highest (75 mg/kg bw) experimental dose caused a significant (p<0.001) increase (7.12+/-0.26 and 9.00+/-0.10, respectively) in comparison with the negative control (0.00+/-0.00). Chromosomes 4 and 19 participated in these Robertsonian translocations. Regarding total cytogenetic changes, a significant increase (p<0.001) was observed in both the intermediate dose group (17.36+/-1.83) and the highest dose group (59.49+/-1.92) compared with the negative control (7.00+/-1.35). These results suggest that fumagillin has genotoxic (clastogenic) potential in mammals in vivo.

Mitochondrial haplotypes of European wild boars with 2n = 36 are closely related to those of European domestic pigs with 2n = 38

Wild boars from Western Europe have a 2n = 36 karyotype, in contrast to a karyotype of 2n = 38 in wild boars from Central Europe and Asia and in all domestic pigs. The phylogenetic status of this wild boar population is unclear, and it is not known if it has contributed to pig domestication. We have now sequenced the mtDNA control region from 30 European wild boars (22 with a confirmed 2n = 36 karyotype) and six Asian wild boars (two Hainan and four Dongbei wild boars) to address this question. The results revealed a close genetic relationship between mtDNA haplotypes from wild boars with 2n = 36 to those from domestic pigs with 2n = 38. Thus, we cannot exclude the possibility that wild boars with 2n = 36 may have contributed to pig domestication despite the karyotype difference. One of the European wild boars carried an Asian mtDNA haplotype, and this most likely reflects gene flow from domestic pigs to European wild boars. However, this gene flow does not appear to be extensive because the frequency of Asian haplotypes detected among European wild boars (c. 3%) were 10-fold lower than among European domestic pigs (c. 30%). Previous studies of mtDNA haplotypes have indicated that pig populations in Europe and Asia have experienced a population expansion, but it is not clear if the expansion occurred before or after domestication. The results of the present study are consistent with an expansion that primarily occurred prior to domestication because the mtDNA haplotypes found in European and Asian wild boars did not form their own clusters but were intermingled with haplotypes found in domestic pigs, indicating that they originated from the same population expansion.

Effects of Nonadditive Genetic Interactions, Inbreeding, and Recessive Defects on Embryo and Fetal Loss by Seventy Days

Lethal recessive genes that cause early embryo loss are difficult to detect. Nonreturn rate at 70 d after first insemination (NR) was evaluated as a trait of the embryo using 1,739,055 first-service records from 1,251 Holstein bulls represented as both service sires and sires of cows. Effects modeled included herd-year-season, parity of cow, sire of cow, service bull, interaction of service bull with sire of cow, and regression on inbreeding of embryo. Variances of service bull and sire of cow were estimated using REML and estimated effects were removed from the data. Interaction variance was estimated from the residuals using the tilde-hat approximation to REML. An additive relationship matrix was used for sire of cow and a dominance relationship matrix for the interaction term. Service bull effects were assumed constant across time and unrelated. For each 10% increase in inbreeding, NR percentage declined by an estimated 1%. A regression of this size could be explained by > 20% of animals carrying defects that cause early embryo loss. Of the total variance, service bull contributed 0.36%; sire of cow, 0.24% (heritability of 1.0%); and interaction, 0.18% (dominance variance of 2.8%). Numbers of records exceeded 500 for 50 bull pair subclasses. Predicted interactions that included effects of inbreeding ranged from - 3.6% to +2.9%, compared with the mean NR of 56%. The largest negative interactions were not caused by known recessive defects. Complex vertebral malformation generally causes loss of pregnancies later in gestation, and few current bulls carry the gene for deficiency of uridine monophosphate synthase. Further study of the families with largest negative interactions could uncover new recessive defects.

Sperm nuclei analysis of 1/29 Robertsonian translocation carrier bulls using fluorescence in situ hybridization

In 1964, Gustavsson and Rockborn first described the 1/29 Robertsonian translocation in cattle. Since then, several studies have demonstrated the negative effect of this particular chromosomal rearrangement on the fertility of carrier animals. During the last decade, meiotic segregation patterns have been studied on human males carrying balanced translocations using FISH on decondensed sperm nuclei. In this work, we have applied the 'Sperm-FISH' technique to determine the chromosomal content of spermatozoa from two bulls heterozygous for the 1/29 translocation and one normal bull (control). 5425 and 2702 sperm nuclei were scored, respectively, for the two heterozygous bulls, using whole chromosome painting probes of chromosomes 1 and 29. Very similar proportions of normal (or balanced) spermatozoa resulting from alternate segregation were observed (97.42% and 96.78%). For both heterozygous bulls, the proportions of nullisomic and disomic spermatozoa did not follow the theoretical 1:1 ratio. Indeed, proportions of nullisomic spermatozoa were higher than those of disomic sperma tozoa (1.40% vs 0.09% (bull 1) and 1.29% vs 0.15% (bull 2) for BTA1, and 0.65% vs 0.40% (bull 1) and 1.11% vs 0.63% (bull 2) for BTA29). The average frequencies of disomic and diploid spermatozoa in the normal bull were 0.11% and 0.05%, respectively.

Complex satellite DNA reshuffling in the polymorphic t(1;29) Robertsonian translocation and evolutionarily derived chromosomes in cattle

We have analysed and mapped physically the satellite I, III (subunits pvu and sau) and IV DNA sequences in cattle using in-situ hybridization. Four breeds were analysed including individuals with a chromosome number of 2n = 60 and individuals with the widespread t(1;29) in the homozygous (2n = 58) and heterozygous state (2n = 59). All three satellite DNA families were present at the centromeres of the many but not all of the autosomal acrocentric chromosomes, and essentially absent from the sex chromosomes. In the translocated t(1;29) chromosome, the satellite DNA families showed a different pattern from that simply derived by fusion of the acrocentric autosomes and loss of satellite sequences, with no variation between breeds. A model of centromeric evolution is presented involving two independent events. Knowledge of mechanisms of translocation formation within cattle is important for a functional understanding of centromere and satellites, investigation of chromosomal abnormalities, and for understanding chromosomal fusion during evolution of other bovids and genome evolution in general.

Frequency and distribution of rob (1;29) in three Portuguese cattle breeds

Representative samples of Portuguese cattle from Barrosã, Maronesa, and Mirandesa breeds underwent cytogenetic investigation. Banding showed that 134 (65.0%) Barrosas, 74 (40.2%) Maronesas and 4 (1.6%) Mirandesas carried rob (1;29). The frequency of this translocation in the three breeds (39% in Barrosas, 23% in Maronesas, and 1% in Mirandesas) was in a genetic Hardy-Weinberg equilibrium for the three karyological forms (2n = 60, 2n = 59 and 2n = 58), strongly supporting the hypothesis for an ancient origin of this translocation and the hypothesis of the origin of Maronesas from Barrosã and Mirandesa cross-breeding.

A new centric fusion translocation in cattle, rob(16;18)

A Barrosã bull (Portugal) has been found to carry a new Robertsonian translocation involving chromosomes 16 and 18 of standard cattle karyotype, as demonstrated by GBG- and RBG-banding techniques. C-banding patterns revealed the dicentric nature of this translocation. A comparison between normal cattle chromosome 16 and the q-arms of translocation chromosome and river buffalo chromosome 5 revealed the same G- and R-banding patterns, with only exception of a pericentromeric G-positive band which has been lost in river buffalo 5q and conserved in normal cattle chromosome 16 and rob(16;18) q-arms.

A new Robertsonian translocation in cattle, rob(16;20)

A new centric fusion translocation, rob(16;20), was discovered in a phenotypically normal bull. C-banding revealed the dicentric nature of this centric fusion. This bull is a descendant of a German red pied bull and a Czechoslovakian red pied cow. Its mother and 26 half-brothers had normal karyotypes, indicating that this translocation arose "de novo".

Centromeric heterochromatin in the cattle rob(1;29) translocation: alpha-satellite I sequences, in-situ MspI digestion patterns, chromomycin staining and C-bands

The centromeric regions and alpha-satellite I sequence were studied on chromosomes 1, 29 and the rob(1;29) translocation in a Portuguese breed of cattle, Barrosa, carrying the translocation. Rob(1;29) centromeric regions showed heterochromatic bands with propidium iodide but, unlike the acrocentric autosomes, no strong centromeric bands were revealed with chromomycin A3. An alpha-satellite I sequence was not found at the centromeres of the X, Y and rob(1;29) chromosomes in the breed, although it was present at the centromeres of all acrocentric chromosomes including 1 and 29. Restriction enzyme banding with MspI revealed polymorphisms between different rob(1;29) chromosomes in both centromeric and intercalary regions. The data show that the centromeric region of the rob(1;29) chromosome has lost the alpha-satellite I sequences, while retaining other heterochromatin, and suggest that this important and widespread translocation has occurred multiple times.

Fertility effects of the 14;20 Robertsonian translocation in cattle

Superovulation and embryo collection procedures were used to study the effect of the 14;20 Robertsonian translocation on fertility and embryo viability. Karyotypes were successfully completed on cells from 77 of the 279 embryos prepared for such analysis. Embryos from 4 cows heterozygous for the translocation were studied. Two bulls with the same condition were studied by using their semen in artificial insemination of cows with normal karyotypes. The proportions of fertilized ova and transferable embryos were not different between cows with the 14;20 translocation and those with normal karyotypes, indicating that fertilization rates were not affected by the translocation. Twenty-two percent of the embryos which were karyotyped had an unbalanced karyotype and would theoretically not have survived to term. All of the theoretically predicted chromosome complements from such a translocation were observed as were three 58,XX,t karyotypes and a 58,XX karyotype. There was no difference in the percentage of embryos with abnormal karyotypes whether the cow or bull was the carrier. Results therefore indicate that fertility is rather severely impaired in carriers of the 14;20 translocation, as was observed with the 1;29 translocation, with most loss due to embryo mortality rather than a lowered conception rate.

Additional evidence of the formation of unbalanced embryos in cattle with the Robertsonian translocation

To confirm the effect of the 7 21 Robertsonian translocation on fertility in Japanese Black Cattle, cytogenetic studies were performed on embryos collected from the following 3 mating groups: normal bull cross normal cow, translocation carrier bull cross normal cow, and normal bull cross translocation carrier cow. All the analyzable embryos showed normal chromosome complements when the parents had a normal karyotype. In the group sired by the 7 21 translocation heterozygous bulls, a total of 56 embryos had metaphases suitable for chromosome analyses. Out of these embryos, 28 had normal chromosome complements and 25 were embryos with a balanced karyotype. However, 3 (5.4%) were monosomic and trisomic embryos, presumably resulting from the fertilization of normal ova by aneuploid spermatozoa. Unbalanced embryos were also observed in the chromosome analyses of embryos derived from the 7 21 translocation heterozygous cows. These results suggest that the 7 21 translocation in the heterozygous state may be associated with a slight reduction in reproductive efficiency.

Use of semen from a bull heterozygous for the translocation in an IVF program

In cattle, a translocation of the Robertsonian type between the largest and smallest chromosome leads to a reduction in fertility. This is substantiated by reduced nonreturn rates in daughter groups of bulls carrying the 1 29 translocation and in the heterozygous bulls themselves. This reduction in fertility is thought to be due to the early death of embryos with unbalanced karyotypes. The influence of semen from a bull known to be heterozygous for the 1 29 translocation on the outcome of a bovine IVF program was investigated. There was a significant difference (P<0.005) in terms of cleavage rate (59.8 vs 71.1%) and blastocyst rate (12.0 vs 20.0%) between the carrier and control bull, respectively. There was no difference in blastocyst quality as measured by cell number. The results observed in vitro are consistent with the field fertility records of the 2 bulls in terms of nonreturn rates (59.2 vs 70.6%, for the carrier and control bull, respectively).

Robertsonian translocation in Sykia Chalkidiki cattle

This is the first report on the Robertsonian 1/29 translocation in the Sykia Chalkidiki cattle breed. The characteristics of this endangered breed are described, and the possibilities of rescuing and exploiting the breed in a zootechnical sense are examined.

Embryonic loss in superovulated cattle caused by the 1;29 Robertsonian translocation

The effect of the 1;29 Robertsonian translocation on fertility was studied using embryos resulting from matings of nine carrier cows and two carrier bulls. Embryos were collected from the following three mating groups utilizing superovulation: normal bull cross normal cow, normal bull cross translocation carrier cow, and translocation carrier bull cross normal cow. The proportion of ova which were fertilized did not vary among the groups, indicating that fertilization rates were not affected by the translocation. The translocation cows did yield fewer embryos on average than did cows with normal karyotypes, which may suggest ovulation rates are reduced (at least after superovulation attempts) in cattle carrying the 1;29 translocation. Twenty of 39 embryos successfully karyotyped had abnormal chromosome complements. All four of the theoretically predicted karyotypes and two additional abnormal combinations were found. Eight of 39 (20.5%) embryos karyotyped had unbalanced karyotypes which would have resulted in embryonic loss. The proportion of embryos with unbalanced karyotypes, was slightly higher when the cow (36%) carried the translocation than when the bull (19%) did. Results of this study indicate that fertility is impaired due to the presence of this translocation. The major loss in reproductive potential appears to be due to embryonic loss rather than fertilization failure.

Production of chimaeric bovine embryos and calves by aggregation of inner cell masses with morulae

Bovine inner cell masses (ICMs) were isolated by immunosurgery at day 8 or 10, or by dissection at day 14, and combined with day-5.5 morulae. Aggregation was obtained between 89%, 62%, and 0% of the day-5:day-8, day-5:day-10, day-5:day-14 composites, respectively. Chromosome analysis of composites, respectively. Chromosome analysis of composites potentially carrying the 1/29 translocation as a chromosome marker and temporarily transferred to the bovine uterus for 8 days showed that chimaeric day-14 embryos can be obtained from day-5:day-8 aggregation. The definitive transfer of eight day-5:day-8 and 11 day-5:day-10 composites resulted in the birth of six and four calves, respectively; five of the six, but none of the four, were chimaeric. The five chimaeras showed mostly the ICM phenotype. The morphological differences between ICMs at different stages of development were examined by electron microscopy and related to the success of the aggregation technique. It is concluded that bovine embryonic cells can regulate for at least 3 days difference in development but not 5 days even though aggregation is still possible.

Genetic diseases of sheep and goats

Congenital malformations and inherited disorders constitute a substantial proportion of the afflictions seen in sheep and goats. Of these, malformations tend to be similar in both species, whereas the genetic diseases encountered to date, with the exception of a few, are different. Of the 28 genetic diseases of sheep and goats described in this review, 60% and 62.5%, respectively, are monogenic disorders. For a majority of the monogenic recessive disorders encountered in these species, the carrier state is not detectable at present, whereas in others, in which a biochemical lesion is known (dermatosparaxis, erythrocyte glutathione deficiency, globoid cell leukodystrophy and glycogen storage disease), the carrier state is detectable with the aid of enzyme and surface protein markers. The latter group and the dominant disorders (anury, cataract, glomerulonephritis, and lethal grey in sheep; gynecomastia and anotia-microtia complex in goats) are easy to eliminate through selective breeding. The polygenic disorders (entropion, epidermolysis bullosa, hereditary chondrodysplasia, and muscular dystrophy of sheep, and udder problems in goats) are more difficult to eradicate, because the mutant genes responsible for these traits generally do not declare themselves until inbreeding brings together a critical concentration to create a health crisis in some, whereas others, which are only short of a few of these mutant genes, might go totally unaffected and therefore undetected. Chromosome defects of the structural nature (translocations) seen in sheep and goats generally create meiotic disturbances, which in a majority of cases lead to subfertility, whereas sex chromosome aneuploids are generally sterile.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased fertility in related females heterozygous for the chromosome translocation

Eighteen heifers and 120 cows which were descendants of a presumed 1/29 carrier Simmental bull were karotyped. Nine heifers (50%) and 48 cows (40%) were found to be heterozygous for the 1/29 translocation (59, XX, t(1q;29q)). The other animals were chromosomally normal (i.e., 60, XX) or not karotyped. The 48 1/29 cows were compared with 72 chromosomally normal cows with regards to days to first conception, calving interval, percentage of calves conceived, percentage of calves weaned and production efficiency (% calved conceived x % calved weaned). Nine carrier heifers were compared to the nine noncarrier heifers as to pregnancy status. Carrier, noncarrier and nonkarotyped relatives were compared to each other and to contemporary females with regard to pregnancy status at their initial exposure to males. The percentage of calves conceived (calving efficiency) in the 72 noncarrier and the 48 females heterozygous for the 1/29 translocation were 81.5 and 74.8%, respectively (P<0.07). Although days to first conception was longer and percentage of calves weaned and production efficiency were lower in the female heterozygous for the 1/29 translocation, the differences were not statistically different (P>0.10) from the noncarriers. Pregnancy rate was 44.4 and 66.7% (P>0.10) for nine carrier and nine noncarrier heifers, respectively. The pregnancy rate of carrier (65.4%), noncarrier (73.2%) and nonkarotyped (77.8%) relatives of this sire at their mating as yearlings, did not differ (P>0.10). The pregnancy rate as yearlings of carrier females (65.4%) and contemporary heifers (79.8%) did differ (P<0.05). Comparing the pregnancy rate as yearlings of all descendants (72.0%) of the Simmental sire to contemporary heifers (79.8%), a significant decrease (P<0.05) was found indicating that fertility of this sire may have been lower than other sires or that other factors beside the translocation affected fertility.

Murine trisomy: developmental profiles of the embryo, and isolation of trisomic cellular systems

Many questions related to the development and the phenotypic expression of trisomy (Ts) are amenable to systematic investigation in a mouse model that allows the induction of Ts 1 to 19 by a breeding design of mice heterozygous for Robertsonian metacentric chromosomes. Some Ts do not survive the first critical phase of organogenesis on days 11 to 12 of fetal development; others as Ts 12, 14, 16, 18, and 19, have a life span until or beyond birth. Model type studies of the morphogenesis of developmental anomalies (e.g. craniocerebral, cardiovascular, or placental) are possible in Ts with a longer developmental span, and Ts 16 of the mouse is considered as a natural model of human trisomy 21. The eventual breakdown and death of the trisomic organism are inevitable. There is considerable interest to find ways for rescue and longer survival of Ts in competitive developmental systems, as e.g., in Ts in equilibrium with 2n blastocyst chimeras, or by isolation of trisomic cellular or tissue systems. Thus, the transfer of Ts hemopoietic stem cells of the fetal liver to irradiated adult recipients is a means of studying the functional capacities and maturation of trisomic hemopoiesis and lymphopoiesis. Both are almost completely restored by Ts 12, 14, 18, and 19 stem cell transplantation with survival periods of more than 6 months. But in other Ts, as of chromosomes 13 or 16, such capacity of reconstitution is impaired. The stepwise analysis of the effects of chromosome triplication on the cell level, in isolated functional systems and in the embryonic organism, is a promising way to understand the phenotypic expression of genome anomalies in complex developmental processes.