Inter and intra-island genetic structure and differentiation of the endemic Bolle's Laurel Pigeon (Columba bollii) in the Canary archipelago.

Islands provide excellent settings for studying the evolutionary history of species, since their geographic isolation and relatively small size limit gene flow between populations, and promote divergence and speciation. The endemic Bolle's Laurel Pigeon Columba bollii is an arboreal frugivorous bird species distributed on laurel forests in four islands of the Canary archipelago. To elucidate the population genetics, we genotyped ten microsatellite loci using DNA obtained from non-invasive samples collected across practically all laurel forest remnants, and subsequently grouped into eight sampling sites. Analyses including F-statistics, Bayesian clustering approaches, isolation by distance tests and population graph topologies, were used to infer the genetic diversity and the population differentiation within and among insular populations. Additionally, we evaluated the effect of null alleles on data analysis. Low genetic diversity was found in all populations of Bolle's Laurel Pigeon, with no significant differences in diversity among them. However, significant genetic differentiation was detected among all populations, with pigeons from La Palma and El Hierro exhibiting the closest affinity. Bayesian clustering supported population separation between islands, and also detected fine-scale structure within the Tenerife and La Gomera populations. Our results suggest that, despite columbids have a high movement ability, they can show signature of genetic divergence among populations, particularly on oceanic islands. Geological history of the islands and distribution range of habitats could have close influence on the evolutionary trajectories of these birds. This approach can provide practical tools to implement appropriate conservation measures for range-restricted species and their habitat.

Molecular sexing of birds using quantitative PCR (qPCR) of sex-linked genes and logistic regression models.

The ability to sex individuals is an important component of many behavioural and ecological investigations and provides information for demographic models used in conservation and species management. However, many birds are difficult to sex using morphological characters or traditional molecular sexing methods. In this study, we developed probabilistic models for sexing birds using quantitative PCR (qPCR) data. First, we quantified distributions of gene copy numbers at a set of six sex-linked genes, including the sex-determining gene DMRT1, for individuals across 17 species and seven orders of birds (n = 150). Using these data, we built predictive logistic models for sex identification and tested their performance with independent samples from 51 species and 13 orders (n = 209). Models using the two loci most highly correlated with sex had greater accuracy than models using the full set of sex-linked loci, across all taxonomic levels of analysis. Sex identification was highly accurate when individuals to be assigned were of species used in model building. Our analytical approach was widely applicable across diverse neognath bird lineages spanning millions of years of evolutionary divergence. Unlike previous methods, our probabilistic framework incorporates uncertainty around qPCR measurements as well as biological variation within species into decision-making rules. We anticipate that this method will be useful for sexing birds, including those of high conservation concern and/or subsistence value, that have proven difficult to sex using traditional approaches. Additionally, the general analytical framework presented in this paper may also be applicable to other organisms with sex chromosomes.

Assessing the Effectiveness of Sex-Linked Molecular Markers to Identify Neomale Breeders for the Production of All-Female Progenies of Rainbow Trout.

A cultured stock of masculinized rainbow trout was diagnosed with Y-linked markers (sdY and OmyY1) aiming to detect neomales before their use at the production level. To achieve a reliable diagnosis, the following steps were considered: (1) PCR amplification of the housekeeping ß-actin gene to determine the DNA quality of samples, (2) validation of the Y-linked markers by their PCR amplification in male and female samples with known sex, and (3) molecular sexing of the masculinized juveniles based on male-specific (XY genotype) and neomale-specific (XX genotype) PCR product band patterns visualized on agarose gel. The validity and concordance of the markers were assessed. The housekeeping gene identified samples with negative PCR amplification revealing a poor DNA quality. The OmyY1 marker presented a more distinctive PCR product band pattern between males and females than the sdY marker and identified a higher proportion of true males (sensitivity = 1.0 and 0.91, respectively). The OmyY1 marker accurately identified 105 neomales of the 198 masculinized individuals on account their consistent and distinctive PCR product band pattern. Among both markers, there was a medium high positive concordance (γ index = 0.7). It is concluded that the OmyY1 marker shows the best performance to reliably detect neomales, a step that is essential to have certified breeders for the production of all-female progenies in fish farming.

Accurate Bayesian inference of sex chromosome karyotypes and sex-linked scaffolds from low-depth sequencing data.

The identification of sex-linked scaffolds and the genetic sex of individuals, i.e. their sex karyotype, is a fundamental step in population genomic studies. If sex-linked scaffolds are known, single individuals may be sexed based on read counts of next-generation sequencing data. If both sex-linked scaffolds as well as sex karyotypes are unknown, as is often the case for non-model organisms, they have to be jointly inferred. For both cases, current methods rely on arbitrary thresholds, which limits their power for low-depth data. In addition, most current methods are limited to euploid sex karyotypes (XX and XY). Here we develop BeXY, a fully Bayesian method to jointly infer the posterior probabilities for each scaffold to be autosomal, X- or Y-linked and for each individual to be any of the sex karyotypes XX, XY, X0, XXX, XXY, XYY and XXYY. If the sex-linked scaffolds are known, it also identifies autosomal trisomies and estimates the sex karyotype posterior probabilities for single individuals. As we show with downsampling experiments, BeXY has higher power than all existing methods. It accurately infers the sex karyotype of ancient human samples with as few as 20,000 reads and accurately infers sex-linked scaffolds from data sets of just a handful of samples or with highly imbalanced sex ratios, also in the case of low-quality reference assemblies. We illustrate the power of BeXY by applying it to both whole-genome shotgun and target enrichment sequencing data of ancient and modern humans, as well as several non-model organisms.

Minimally Invasive Sampling Methods for Molecular Sexing of Wild and Companion Birds.

Birds are highly social and must be paired in order to increase their welfare. Most bird species are monomorphic; therefore, molecular sexing helps provide appropriate welfare for birds. Moreover, early sex determination can be of great value for bird owners. The aim of this study was to demonstrate that sex identification in birds achieved using molecular methods and samples collected via minimally invasive methods is fast, efficient, and accurate. A total of 100 samples (29 paired samples of feathers and oral swabs and 14 tripled samples of feathers, oral swabs, and blood) from 43 birds were included in this study, as follows: wild birds (Falconiformes, Accipitriformes, landfowl-Galliformes, waterfowl-Anseriformes) and companion birds (Passeriformes, Psittaciformes-large-, medium-, and small-sized parrots). Amplification of CHD1-Z and CHD1-W genes was performed via conventional PCR. The results obtained from feathers were compared to those obtained from oral swabs and to those obtained from blood samples, where applicable. The obtained results show that all types of samples can be used for molecular sexing of all studied bird species. To the best of our knowledge, the present study reports, for the first time, molecular sex identification in Red Siskin (Carduelis cucullata) and Goldfinch (Carduelis carduelis major). For higher accuracy, our recommendation is to use minimally invasive samples (oral swabs and feathers) and to test both types of samples for each bird instead of blood samples.

Long-term female bias in sex ratios across life stages of Harpy Eagle, a large raptor exhibiting reverse sexual size dimorphism.

The primary (PSR), secondary (SSR) and adult (ASR) sex ratios of sexually reproducing organisms influence their life histories. Species exhibiting reversed sexual size dimorphism (RSD) may imply a higher cost of female production or lower female survival, thus generating biases in PSR, SSR and/or ASR towards males. The Harpy Eagle is the world's largest eagle exhibiting RSD. This species is found in the Neotropical region and is currently threatened with extinction. We used molecular markers to determine the sex of 309 Harpy Eagles spanning different life stages-eaglets, subadults and adults-from 1904 to 2021 within the Amazon Rainforest and Atlantic Forest. Sex ratios for all life stages revealed a female-biased deviation across all periods and regions. Our results suggest that the population bias towards females is an evolutionary ecological pattern of this species, and SSR and ASR likely emerged from the PSR. This natural bias towards females may be compensated by an earlier sexual maturation age of males, implying a longer reproductive lifespan and a higher proportion of sexually active males. A better understanding of the Harpy Eagle's life history can contribute to understanding sex-role evolution and enable more appropriate conservation strategies for the species.

Identification of sex-linked SNP markers in wild populations of monomorphic birds.

Single-nucleotide polymorphism (SNP) analysis is a powerful tool for population genetics, pedigree reconstruction and phenotypic trait mapping. However, the untapped potential of SNP markers to discriminate the sex of individuals in species with reduced sexual dimorphism or of individuals during immature stages remains a largely unexplored avenue. Here, we developed a novel protocol for molecular sexing of birds based on the detection of unique Z- and W-linked SNP markers. Our method is based on the identification of two unique loci, one in each sexual chromosome. Individuals are considered males when they show no calls for the W-linked SNP and are heterozygous or homozygous for the Z-linked SNP, while females exhibit both Z- and W-linked SNP calls. We validated the method in the Jackdaw (Corvus monedula). The reduced sexual dimorphism in this species makes it difficult to identify the sex of individuals in the wild. We assessed the reliability of the method using 36 individuals of known sex and found that their sex was correctly assigned in 100% of cases. The sex-linked markers also proved to be widely applicable for discriminating males and females from a sample of 927 genotyped individuals at different maturity stages, with an accuracy of 99.5%. Since SNP markers are increasingly used in quantitative genetic analyses of wild populations, the approach we propose has great potential to be integrated into broader genetic research programmes without the need for additional sexing techniques.

Sex-Associated SNP Confirmation of Sex-Reversed Male Farmed Japanese Flounder Paralichthys olivaceus.

Female Japanese flounder Paralichthys olivaceus grow more rapidly than the male. The goal of all-female commercial production requires an efficient method of genetic sex identification. We conducted genome-wide association analysis of female and male farmed Japanese flounder (n = 24 per phenotypic sex) and found all regions of chromosome 24 to be significantly associated with phenotypic sex, suggesting it as the sex chromosome. Genetic sex was identified based on single nucleotide polymorphisms (SNP) on chromosome 24 (n = 3568) using multidimensional scaling analysis, and individuals were clearly separated according to sex by the first dimension. The 61 SNPs most highly associated with sex were selected, and an amplicon-based SNP panel was developed. This was used to determine genetic sex of 39 females and 40 males. Eleven phenotypic males were assigned as female with XX genotype, suggesting sex reversal. Genetic sex was also assessed based on the indel of the amh gene promoter, which is the major candidate sex gene of Japanese flounder. We found four SNPs perfectly associated with genotypic sex in the sex-associated SNP panel, one of which was located in exon 2 of the amh gene. Along with the indel of the amh gene promoter, the sex-associated SNP panel will be of value in identifying genetic sex of farmed Japanese flounder. Molecular sexing will facilitate all-female production by breeding sex-reversed males.

Easy-to-use R functions to separate reduced-representation genomic datasets into sex-linked and autosomal loci, and conduct sex assignment.

Identifying sex-linked markers in genomic datasets is important because their presence in supposedly neutral autosomal datasets can result in incorrect estimates of genetic diversity, population structure and parentage. However, detecting sex-linked loci can be challenging, and available scripts neglect some categories of sex-linked variation. Here, we present new R functions to (1) identify and separate sex-linked loci in ZW and XY sex determination systems and (2) infer the genetic sex of individuals based on these loci. We tested these functions on genomic data for two bird and one mammal species and compared the biological inferences made before and after removing sex-linked loci using our function. We found that our function identified autosomal loci with ≥98.8% accuracy and sex-linked loci with an average accuracy of 87.8%. We showed that standard filters, such as low read depth and call rate, failed to remove up to 54.7% of sex-linked loci. This led to (i) overestimation of population FIS by up to 24%, and the number of private alleles by up to 8%; (ii) wrongly inferring significant sex differences in heterozygosity; (iii) obscuring genetic population structure and (iv) inferring ~11% fewer correct parentages. We discuss how failure to remove sex-linked markers can lead to incorrect biological inferences (e.g. sex-biased dispersal and cryptic population structure) and misleading management recommendations. For reduced-representation datasets with at least 15 known-sex individuals of each sex, our functions offer convenient resources to remove sex-linked loci and to sex the remaining individuals (freely available at https://github.com/drobledoruiz/conservation_genomics).

Non-Invasive Sex Determination of Nestlings and Adult Bonelli's Eagles Using Morphometrics.

Biometric analysis allows the sexing of most vertebrates, particularly birds. Birds of prey, and, especially, the Bonelli's eagle (Aquila fasciata), show reverse sexual dimorphism (i.e., females are usually larger than males). In contrast to blood sampling, the use of morphometrics allows sex determination using a non-invasive method, and, therefore, it facilitates fieldwork. By means of a linear discriminant analysis of biometric variables, we obtained different equations that allow the sexing of nestlings and adult Bonelli's eagles. We sampled 137 Bonelli's eagles, 82 nestlings and 55 adults in eastern Spain during the period 2015-2022. The sexes obtained after linear discriminant analysis were compared with their molecular sexing. The validation procedure of the linear discriminant equations facilitated the reduction of the number of variables used and, consequently, optimised working time and sexing accuracy. After validation, some equations showed a 100% sexing efficiency for Bonelli's eagles, particularly for adults. Our results showed that the variables with smaller overlap between the sexes were the lateral tarsus length and dorso-ventral tarsus length, particularly in nestlings. The rest of the variables showed some overlap between the sexes in both age classes. The results we obtained enable the sexing of juvenile and adult Bonelli's eagles in the field using just these two measurements. Hence, this is an easy, accurate, quick and non-invasive method with multiple applications, including in studies on population dynamics, survival analysis or extinction risk assessments, which, ultimately, could contribute to the improvement of the conservation status of this endangered species.

Effect of storage temperature and duration on direct PCR amplification of various feather types and DBS matrices.

The use of direct PCR has been pioneered over the last decade for DNA analysis of biological specimens of distinct origins. The information on how longer these specimens can be stored and amplified by direct PCR is however scanty. Such a piece of information could expedite research and diagnostic studies without compromising the reliability of results. The current study was therefore designed to analyze the effect of storage temperature and duration on direct PCR amplification of biological specimens having either low quantity or high quantity of DNA. Whole blood, dried blood spots (DBS), and feathers from chicken were stored for five years at three different temperatures, viz. room temperature (∼25 °C), 4 °C, and -20 °C. These samples were subjected to crude DNA extraction by diluting them in PBS buffer and heating at 98 °C after 1 day, 7 days, 15 days, 1 month, 3 months, 6 months, 1 year, 3 years and 5 years of storage. The crude DNA was PCR-amplified with the use of DNA sexing primers as well as DNA barcoding primers. Incubation at 98 °C for 10 min of any type of sample in PBS buffer was sufficient for crude DNA extraction. There was irrelevant impact of feather type, DBS matrix nature and storage temperature on amplification success over the period of analysis. It was possible to successfully accomplish the amplification of 96 samples with the use of routine PCR reagents within 3.5-6.0 hrs. In short, economical and fast genetic analysis of commonly used avian samples is feasible after their storage for longer time at room temperature.

Sex ratio and relatedness in the Griffon vulture (Gyps fulvus) population of Serbia.

Background: Once a widespread species across the region of Southeast Europe, the Griffon vulture is now confined to small and isolated populations across the Balkan Peninsula. The population from Serbia represents its biggest and most viable population that can serve as an important reservoir of genetic diversity from which the birds can be used for the region's reintroduction programmes. The available genetic data for this valuable population are scarce and as a protected species that belongs to the highly endangered vulture group, it needs to be well described so that it can be properly managed and used as a restocking population. Considering the serious recent bottleneck event that the Griffon vulture population from Serbia experienced we estimated the overall relatedness among the birds from this population. Sex ratio, another important parameter that shows the vitality and strength of the population was evaluated as well. Methods: During the annual monitoring that was performed in the period from 2013-2021, we collected blood samples from individual birds that were marked in the nests. In total, 169 samples were collected and each was used for molecular sexing while 58 presumably unrelated birds from different nests were used for inbreeding and relatedness analyses. The relatedness was estimated using both biparentally (10 microsatellite loci) and uniparentally (Cytb and D-loop I of mitochondrial DNA) inherited markers. Results: The level of inbreeding was relatively high and on average it was 8.3% while the mean number of relatives for each bird was close to three. The sex ratio was close to 1:1 and for the analysed period of 9 years, it didn't demonstrate a statistically significant deviation from the expected ratio of 1:1, suggesting that this is a stable and healthy population. Our data suggest that, even though a relatively high level of inbreeding can be detected among the individual birds, the Griffon vulture population from Serbia can be used as a source population for restocking and reintroduction programmes in the region. These data combined with previously observed genetic differentiation between the populations from the Iberian and Balkan Peninsulas suggest that the introduction of foreign birds should be avoided and that local birds should be used instead.

How low can you go? Introducing SeXY: sex identification from low-quantity sequencing data despite lacking assembled sex chromosomes.

Accurate sex identification is crucial for elucidating the biology of a species. In the absence of directly observable sexual characteristics, sex identification of wild fauna can be challenging, if not impossible. Molecular sexing offers a powerful alternative to morphological sexing approaches. Here, we present SeXY, a novel sex-identification pipeline, for very low-coverage shotgun sequencing data from a single individual. SeXY was designed to utilize low-effort screening data for sex identification and does not require a conspecific sex-chromosome assembly as reference. We assess the accuracy of our pipeline to data quantity by downsampling sequencing data from 100,000 to 1000 mapped reads and to reference genome selection by mapping to a variety of reference genomes of various qualities and phylogenetic distance. We show that our method is 100% accurate when mapping to a high-quality (highly contiguous N50 > 30 Mb) conspecific genome, even down to 1000 mapped reads. For lower-quality reference assemblies (N50 < 30 Mb), our method is 100% accurate with 50,000 mapped reads, regardless of reference assembly quality or phylogenetic distance. The SeXY pipeline provides several advantages over previously implemented methods; SeXY (i) requires sequencing data from only a single individual, (ii) does not require assembled conspecific sex chromosomes, or even a conspecific reference assembly, (iii) takes into account variation in coverage across the genome, and (iv) is accurate with only 1000 mapped reads in many cases.

Labile sex chromosomes in the Australian freshwater fish family Percichthyidae.

Sex-specific ecology has management implications, but rapid sex-chromosome turnover in fishes hinders sex-marker development for monomorphic species. We used annotated genomes and reduced-representation sequencing data for two Australian percichthyids, Macquarie perch Macquaria australasica and golden perch M. ambigua, and whole genome resequencing for 50 Macquarie perch of each sex, to identify sex-linked loci and develop an affordable sexing assay. In silico pool-seq tests of 1,492,004 Macquarie perch SNPs revealed that a 275-kb scaffold was enriched for gametologous loci. Within this scaffold, 22 loci were sex-linked in a predominantly XY system, with females being homozygous for the X-linked allele at all 22, and males having the Y-linked allele at >7. Seven XY-gametologous loci (all males, but no females, are heterozygous or homozygous for the male-specific allele) were within a 146-bp region. A PCR-RFLP sexing assay targeting one Y-linked SNP, tested in 66 known-sex Macquarie perch and two of each sex of three confamilial species, plus amplicon sequencing of 400 bp encompassing the 146-bp region, revealed that the few sex-linked positions differ between species and between Macquarie perch populations. This indicates sex-chromosome lability in Percichthyidae, supported by nonhomologous scaffolds containing sex-linked loci for Macquarie- and golden perches. The present resources facilitate genomic research in Percichthyidae, including formulation of hypotheses about candidate genes of interest such as transcription factor SOX1b that occurs in the 275-kb scaffold ~38 kb downstream of the 146-bp region containing seven XY-gametologous loci. Sex-linked markers will be useful for determining genetic sex in some populations and studying sex chromosome turnover.

Mosquito blood-feeding patterns and nesting behavior of American crows, an amplifying host of West Nile virus.

BACKGROUND: Although American crows are a key indicator species for West Nile virus (WNV) and mount among the highest viremias reported for any host, the importance of crows in the WNV transmission cycle has been called into question because of their consistent underrepresentation in studies of Culex blood meal sources. Here, we test the hypothesis that this apparent underrepresentation could be due, in part, to underrepresentation of crow nesting habitat from mosquito sampling designs. Specifically, we examine how the likelihood of a crow blood meal changes with distance to and timing of active crow nests in a Davis, California, population. METHODS: Sixty artificial mosquito resting sites were deployed from May to September 2014 in varying proximity to known crow nesting sites, and Culex blood meal hosts were identified by DNA barcoding. Genotypes from crow blood meals and local crows (72 nestlings from 30 broods and 389 local breeders and helpers) were used to match mosquito blood meals to specific local crows. RESULTS: Among the 297 identified Culex blood meals, 20 (6.7%) were attributable to crows. The mean percentage of blood meals of crow origin was 19% in the nesting period (1 May-18 June 2014), but 0% in the weeks after fledging (19 June-1 September 2014), and the likelihood of a crow blood meal increased with proximity to an active nest: the odds that crows hosted a Culex blood meal were 38.07 times greater within 10 m of an active nest than > 10 m from an active nest. Nine of ten crow blood meals that could be matched to a genotype of a specific crow belonged to either nestlings in these nests or their mothers. Six of the seven genotypes that could not be attributed to sampled birds belonged to females, a sex bias likely due to mosquitoes targeting incubating or brooding females. CONCLUSION: Data herein indicate that breeding crows serve as hosts for Culex in the initial stages of the WNV spring enzootic cycle. Given their high viremia, infected crows could thereby contribute to the re-initiation and early amplification of the virus, increasing its availability as mosquitoes shift to other moderately competent later-breeding avian hosts.

hiphop: Improved paternity assignment among close relatives using a simple exclusion method for biallelic markers.

Assignment of parentage with molecular markers is most difficult when the true parents have close relatives in the adult population. Here, we present an efficient solution to that problem by extending simple exclusion approaches to parentage analysis with single nucleotide polymorphic markers (SNPs). We augmented the previously published homozygote opposite test (hot), which counts mismatches due to the offspring and candidate parent having different homozygous genotypes, with an additional test. In this case, parents homozygous for the same SNP are incompatible with heterozygous offspring (i.e., "Homozygous Identical Parents, Heterozygous Offspring are Precluded": hiphop). We tested this approach in a cooperatively breeding bird, the superb fairy-wren, Malurus cyaneus, where rates of extra-pair paternity are exceptionally high, and where paternity assignment is challenging because breeding males typically have first-order adult relatives in their neighbourhood. Combining the tests and conditioning on the maternal genotype with a set of 1376 autosomal SNPs always allowed us to distinguish a single most likely sire from his relatives, and also to identify cases where the true sire must have been unsampled. In contrast, if just the hot test was used, we failed to identify a single most-likely sire in 2.5% of cases. Resampling enabled us to create guidelines for the number of SNPs required when first-order relatives coexist in the mating pool. Our method, implemented in the R package hiphop, therefore provides unambiguous parentage assignments even in systems with complex social organisation. We also identified a suite of Z- and W-linked SNPs that always identified sex correctly.

Long-term stability of sex chromosome gene content allows accurate qPCR-based molecular sexing across birds.

Embryos, juveniles, and even adults of many bird species lack pronounced external sexually dimorphic characteristics. Accurate identification of sex is crucial for research (e.g., developmental, population, and evolutionary studies), management of wildlife species, and captive breeding programmes for both conservation and poultry. An accurate molecular sexing method applicable across the entire bird radiation is theoretically possible thanks to the long-term stability of their ZZ/ZW sex chromosomes, but current methods are not applicable in a wide range of bird lineages. Here, we developed a novel molecular sexing method based on the comparison of gene copy number variation by quantitative real-time PCR (qPCR) in conserved Z-specific genes (CHRNA6, DDX4, LPAR1, TMEM161B, VPS13A), i.e. genes linked to Z but absent from W chromosomes. We tested the method across three paleognath and 70 neognath species covering the avian phylogeny. In addition, we designed primers for four Z-specific genes (DOCK8, FUT10, PIGG and PSD3) for qPCR-based molecular sexing in three paleognath species. We have demonstrated that the genes DOCK8, FUT10, PIGG and PSD3 can identify sex in paleognath birds and the genes CHRNA6, DDX4, TMEM161B, and VPS13A can reveal sex in neognath birds. The gene LPAR1 can be used to accurately identify sex in both paleognath and neognath species. Along with outlining a novel method of practical importance for molecular sexing in birds, our study also documents in detail the conservation of sex chromosomes across the avian phylogeny.

Poorly differentiated XX/XY sex chromosomes are widely shared across skink radiation.

Differentiated sex chromosomes are believed to be evolutionarily stable, while poorly differentiated sex chromosomes are considered to be prone to turnovers. With around 1700 currently known species forming ca 15% of reptile species diversity, skinks (family Scincidae) are a very diverse group of squamates known for their large ecological and morphological variability. Skinks generally have poorly differentiated and cytogenetically indistinguishable sex chromosomes, and their sex determination was suggested to be highly variable. Here, we determined X-linked genes in the common sandfish (Scincus scincus) and demonstrate that skinks have shared the same homologous XX/XY sex chromosomes across their wide phylogenetic spectrum for at least 85 million years, approaching the age of the highly differentiated ZZ/ZW sex chromosomes of birds and advanced snakes. Skinks thus demonstrate that even poorly differentiated sex chromosomes can be evolutionarily stable. The conservation of sex chromosomes across skinks allows us to introduce the first molecular sexing method widely applicable in this group.

Comparison of Cell-Free Fetal DNA Plasma Content Used to Sex Determination Between Three Trimesters of Pregnancy in Torkaman Pregnant Mare.

This investigation aimed to compare the cell-free fetal DNA (cffDNA) plasma present in three trimesters of pregnancy in Torkaman pregnant mare. Peripheral blood samples of 32 pregnant mares in three trimesters of pregnancy were collected in tubes containing ethylenediaminetetraacetic acid at three time points. Circulating cffDNA was extracted from 3 mL of maternal plasma. Using outer and inner primers, a conventional polymerase chain reaction was performed for the sex-determining region Y (SRY) gene present in the Y chromosome. Of the total 32 Torkaman pregnant mares, 24 were carrying male fetuses and eight were carrying female fetuses. In total, the accuracy of the test was 48.75%, 68.75%, and 75% in the first, second, and third trimesters of pregnancy, respectively. The sensitivities were 25%, 58.32%, and 66.66%, respectively, whereas their specificities were 100% in all trimesters. In conclusion, the SRY gene can permit the detection of equine fetal sex with good accuracy through cffDNA analysis in maternal plasma just in the third trimester of pregnancy, although specificity in all duration of pregnancy was 100%.