Mendelian Expectations Research Articles

Inheritance and ecological effects of exogenous genes from transgenic Brassica napus to Brassica juncea hybrids

●With the rapid development of new breeding techniques, the ecological impacts of transgenic plants receive wide concern again, particularly for potential gene flow from transgenic crops to their relatives. The transgene insertion position, number of gene copies, and flanking sequence of exogenous genes integrated into the recipient genome affect the genetic stability and fitness of offspring.●We employed hybrids F1 and F2, six backcross generations BC1-BC6 and BC1F1 from transgenic Brassica napus with Bacillus thuringiensis (Bt) cry1Ac gene and its wild relative B. juncea through hand pollination. We detected exogenous gene copies, mRNA transcription, and protein expression by ddPCR, qRT-PCR and ELISA, and the fitness of hybrid and backcross generations.●Exogenous genes followed Mendelian segregation expectations in hybrid and backcrossed generations, with stable gene copies, mRNA transcription and protein concentration of exogenous genes in offspring. Exogenous gene copies had no significant effects on plant fitness, but had positive effects on mRNA transcription and protein concentration that varied with growth stages in hybrid and backcross generations.●Our study demonstrated inheritance and ecological effects of exogenous genes from transgenic plants to wild relatives, which will help ecological risk management of biotechnological plants released in the nature.

Mapping quantitative trait loci for seminal root angle in a selected durum wheat population.

Seminal root angle (SRA) is an important root architectural trait associated with drought adaptation in cereal crops. To date, all attempts to dissect the genetic architecture of SRA in durum wheat (Triticum durum Desf.) have used large association panels or structured mapping populations. Identifying changes in allele frequency generated by selection provides an alternative genetic mapping approach that can increase the power and precision of QTL detection. This study aimed to map quantitative trait loci (QTL) for SRA by genotyping durum lines created through divergent selection using a combination of marker-assisted selection (MAS) for the major SRA QTL (qSRA-6A) and phenotypic selection for SRA over multiple generations. The created 11 lines (BC1F2:5) were genotyped with genome-wide single-nucleotide polymorphism (SNP) markers to map QTL by identifying markers that displayed segregation distortion significantly different from the Mendelian expectation. QTL regions were further assessed in an independent validation population to confirm their associations with SRA. The experiment revealed 14 genomic regions under selection, 12 of which have not previously been reported for SRA. Five regions, including qSRA-6A, were confirmed in the validation population. The genomic regions identified in this study indicate that the genetic control of SRA is more complex than previously anticipated. Our study demonstrates that selection mapping is a powerful approach to complement genome-wide association studies for QTL detection. Moreover, the verification of qSRA-6A in an elite genetic background highlights the potential for MAS, although it is necessary to combine additional QTL to develop new cultivars with extreme SRA phenotypes.

Together inbreeding and reproductive compensation favor lethal t-haplotypes.

Male mice who are heterozygous for distorting and non-distorting alleles at the t-haplotype transmit the driving t-haplotype around 90% of the time-a drastic departure from Mendelian expectations. This selfish act comes at a cost. The mechanism underlying transmission distortion in this system causes severe sterility in males homozygous for the drive alleles, ultimately preventing its fixation. Curiously, many driving t-haplotypes also induce embryonic lethality in both sexes when homozygous; however, this is neither universal nor a necessity for this distortion mechanism. Charlesworth provided an adaptive explanation for the evolution of lethal t-haplotypes in a population segregating for distorting and non-distorting t alleles-if mothers compensate by replacing dead embryos with new offspring (or by transferring energy to surviving offspring), a recessive lethal can be favored because it effectively allows mothers the opportunity to trade in infertile males for potentially fertile offspring. This model, however, requires near complete reproductive compensation for the invasion of the lethal t-haplotype and produces an equilibrium frequency of lethal drivers well below what is observed in nature. We show that low levels of systemic inbreeding, which we model as brother-sister mating, allow lethal t-haplotypes to invade with much lower levels of reproductive compensation. Furthermore, inbreeding allows these lethal haplotypes to largely displace the ancestral male-sterile haplotypes. Our results show that together inbreeding and reproductive compensation move expected equilibria closer to observed haplotype frequencies in natural populations and occur under lower, potentially more reasonable, parameters.

Paramutation at the maize pl1 locus is associated with RdDM activity at distal tandem repeats.

Exceptions to Mendelian inheritance often highlight novel chromosomal behaviors. The maize Pl1-Rhoades allele conferring plant pigmentation can display inheritance patterns deviating from Mendelian expectations in a behavior known as paramutation. However, the chromosome features mediating such exceptions remain unknown. Here we show that small RNA production reflecting RNA polymerase IV function within a distal downstream set of five tandem repeats is coincident with meiotically-heritable repression of the Pl1-Rhoades transcription unit. A related pl1 haplotype with three, but not one with two, repeat units also displays the trans-homolog silencing typifying paramutations. 4C interactions, CHD3a-dependent small RNA profiles, nuclease sensitivity, and polyadenylated RNA levels highlight a repeat subregion having regulatory potential. Our comparative and mutant analyses show that transcriptional repression of Pl1-Rhoades correlates with 24-nucleotide RNA production and cytosine methylation at this subregion indicating the action of a specific DNA-dependent RNA polymerase complex. These findings support a working model in which pl1 paramutation depends on trans-chromosomal RNA-directed DNA methylation operating at a discrete cis-linked and copy-number-dependent transcriptional regulatory element.

Testing a candidate meiotic drive locus identified by pool sequencing.

Meiotic drive biases the transmission of alleles in heterozygous individuals, such that Mendel's law of equal segregation is violated. Most examples of meiotic drive have been discovered over the past century based on causing sex ratio distortion or the biased transmission of easily scoreable genetic markers that were linked to drive alleles. More recently, several approaches have been developed that attempt to identify distortions of Mendelian segregation genome wide. Here, we test a candidate female meiotic drive locus in Drosophila melanogaster, identified previously as causing a ∼54:46 distortion ratio using sequencing of large pools of backcross progeny. We inserted fluorescent visible markers near the candidate locus and scored transmission in thousands of individual progeny. We observed a small but significant deviation from the Mendelian expectation; however, it was in the opposite direction to that predicted based on the original experiments. We discuss several possible causes of the discrepancy between the 2 approaches, noting that subtle viability effects are particularly challenging to disentangle from potential small-effect meiotic drive loci. We conclude that pool sequencing approaches remain a powerful method to identify candidate meiotic drive loci but that genotyping of individual progeny at early developmental stages may be required for robust confirmation.

Distortion of Mendelian segregation across the Angus cattle genome uncovering regions affecting reproduction

Nowadays, the availability of genotyped trios (sire-dam-offspring) in the livestock industry enables the implementation of the transmission ratio distortion (TRD) approach to discover deleterious alleles in the genome. Various biological mechanisms at different stages of the reproductive cycle such as gametogenesis, embryo development and postnatal viability can induce signals of TRD (i.e., deviation from Mendelian inheritance expectations). In this study, TRD was evaluated using both SNP-by-SNP and sliding windows of 2-, 4-, 7-, 10- and 20-SNP across 92,942 autosomal SNPs for 258,140 genotyped Angus cattle including 7,486 sires, 72,688 dams and 205,966 offspring. Transmission ratio distortion was characterized using allelic (specific- and unspecific-parent TRD) and genotypic parameterizations (additive- and dominance-TRD). Across the Angus autosomal chromosomes, 851 regions were clearly found with decisive evidence for TRD. Among these findings, 19 haplotypes with recessive patterns (potential lethality for homozygote individuals) and 52 regions with allelic patterns exhibiting complete or quasi-complete absence for homozygous individuals in addition to under-representation (potentially reduced viability) of the carrier (heterozygous) offspring were found. In addition, 64 (12) and 20 (4) regions showed significant influence on the trait heifer pregnancy at p-value < 0.05 (after chromosome-wise false discovery rate) and 0.01, respectively, reducing the pregnancy rate up to 15%, thus, supporting the biological importance of TRD phenomenon in reproduction.

Unravelling transmission ratio distortion across the bovine genome: identification of candidate regions for reproduction defects

BackgroundBiological mechanisms affecting gametogenesis, embryo development and postnatal viability have the potential to alter Mendelian inheritance expectations resulting in observable transmission ratio distortion (TRD). Although the discovery of TRD cases have been around for a long time, the current widespread and growing use of DNA technologies in the livestock industry provides a valuable resource of large genomic data with parent–offspring genotyped trios, enabling the implementation of TRD approach. In this research, the objective is to investigate TRD using SNP-by-SNP and sliding windows approaches on 441,802 genotyped Holstein cattle and 132,991 (or 47,910 phased) autosomal SNPs.ResultsThe TRD was characterized using allelic and genotypic parameterizations. Across the whole genome a total of 604 chromosomal regions showed strong significant TRD. Most (85%) of the regions presented an allelic TRD pattern with an under-representation (reduced viability) of carrier (heterozygous) offspring or with the complete or quasi-complete absence (lethality) for homozygous individuals. On the other hand, the remaining regions with genotypic TRD patterns exhibited the classical recessive inheritance or either an excess or deficiency of heterozygote offspring. Among them, the number of most relevant novel regions with strong allelic and recessive TRD patterns were 10 and 5, respectively. In addition, functional analyses revealed candidate genes regulating key biological processes associated with embryonic development and survival, DNA repair and meiotic processes, among others, providing additional biological evidence of TRD findings.ConclusionsOur results revealed the importance of implementing different TRD parameterizations to capture all types of distortions and to determine the corresponding inheritance pattern. Novel candidate genomic regions containing lethal alleles and genes with functional and biological consequences on fertility and pre- and post-natal viability were also identified, providing opportunities for improving breeding success in cattle.

Transmission ratio distortion regions in the context of genomic evaluation and their effects on reproductive traits in cattle

Transmission ratio distortion (TRD), which is a deviation from Mendelian expectations, has been associated with basic mechanisms of life such as sperm and ova fertility and viability at developmental stages of the reproductive cycle. In this study different models including TRD regions were tested for different reproductive traits [days from first service to conception (FSTC), number of services, first service nonreturn rate (NRR), and stillbirth (SB)]. Thus, in addition to a basic model with systematic and random effects, including genetic effects modeled through a genomic relationship matrix, we developed 2 additional models, including a second genomic relationship matrix based on TRD regions, and TRD regions as a random effect assuming heterogeneous variances. The analyses were performed with 10,623 cows and 1,520 bulls genotyped for 47,910 SNPs, 590 TRD regions, and several records ranging from 9,587 (FSTC) to 19,667 (SB). The results of this study showed the ability of TRD regions to capture some additional genetic variance for some traits; however, this did not translate into higher accuracy for genomic prediction. This could be explained by the nature of TRD itself, which may arise in different stages of the reproductive cycle. Nevertheless, important effects of TRD regions were found on SB (31 regions) and NRR (18 regions) when comparing at-risk versus control matings, especially for regions with allelic TRD pattern. Particularly for NRR, the probability of observing nonpregnant cow increases by up to 27% for specific TRD regions, and the probability of observing stillbirth increased by up to 254%. These results support the relevance of several TRD regions on some reproductive traits, especially those with allelic patterns that have not received as much attention as recessive TRD patterns.

Parent-offspring genotyped trios unravelling genomic regions with gametic and genotypic epistatic transmission bias on the cattle genome.

Several biological mechanisms affecting the sperm and ova fertility and viability at developmental stages of the reproductive cycle resulted in observable transmission ratio distortion (i.e., deviation from Mendelian expectations). Gene-by-gene interactions (or epistasis) could also potentially cause specific transmission ratio distortion patterns at different loci as unfavorable allelic combinations are under-represented, exhibiting deviation from Mendelian proportions. Here, we aimed to detect pairs of loci with epistatic transmission ratio distortion using 283,817 parent-offspring genotyped trios (sire-dam-offspring) of Holstein cattle. Allelic and genotypic parameterization for epistatic transmission ratio distortion were developed and implemented to scan the whole genome. Different epistatic transmission ratio distortion patterns were observed. Using genotypic models, 7, 19 and 6 pairs of genomic regions were found with decisive evidence with additive-by-additive, additive-by-dominance/dominance-by-additive and dominance-by-dominance effects, respectively. Using the allelic transmission ratio distortion model, more insight was gained in understanding the penetrance of single-locus distortions, revealing 17 pairs of SNPs. Scanning for the depletion of individuals carrying pairs of homozygous genotypes for unlinked loci, revealed 56 pairs of SNPs with recessive epistatic transmission ratio distortion patterns. The maximum number of expected homozygous offspring, with none of them observed, was 23. Finally, in this study, we identified candidate genomic regions harboring epistatic interactions with potential biological implications in economically important traits, such as reproduction.

Comparative transmission genetics of introgressed chromatin in reciprocal advanced backcross populations in Gossypium (cotton) polyploids.

Introgression is a potential source of valuable genetic variation and interspecific introgression lines are important resources for plant breeders to access novel alleles. Experimental advanced-generation backcross populations contain individuals with genomic compositions similar to those resulting from natural interspecific hybridization and provide opportunities to study the nature and transmission pattern of donor chromatin in recipient genomes. Here, we analyze transmission of donor chromatin in reciprocal backcrosses between G. hirsutum and G. barbadense. Across the genome, recurrent backcrossing in both backgrounds yielded donor chromatin at slightly higher frequencies than the Mendelian expectation in BC5F1 plants, while the average frequency of donor alleles in BC5F2 segregating families was less than expected. In the two subgenomes of polyploid cotton, the rate of donor chromatin introgression was similar. Although donor chromatin was tolerated over much of the recipient genomes, 21 regions recalcitrant to donor alleles were identified. Only limited correspondence is observed between the recalcitrant regions in the two backgrounds, suggesting the effect of species background on introgression of donor segments. Genetic breakdown was progressive, with floral abscission and seed inviability ongoing during backcrossing cycles. Regions of either high or low introgression tended to be in terminal chromosomal regions that are generally rich in both genes and crossover events, with long stretches around the centromere having limited crossover activity resulting in relatively constant low introgression frequencies. Constraints on fixation and selection of donor alleles highlights the challenges of utilizing introgression breeding in crop improvement.

Within-family variation in larval viability and growth is controlled by different genes: a case study with Crassostrea gigas

Variation in growth and survival of planktonic larvae has profound effects on marine population abundance. Environmental causes of differential larval growth and mortality are well studied, but genetic variation in these traits is less well understood. Here, we reveal genetic variation in survival and growth of full-sib larvae of the Pacific oyster Crassostrea gigas reared under identical conditions. We size-selected 1.42 million, 24 d old larvae to produce small, medium, and large size classes, constituting 93% of the population. Parental tissues and a total of 144 larvae sampled from each size class were individually genotyped with a panel of 45 mapped DNA markers. Consistent with previous work, 11 markers had genotypic frequencies that differed significantly from their Mendelian expectations and, upon mapping, are explained by 6 viability quantitative trait loci (vQTL). Notably, shell-length variance among size classes maps to 6 major growth QTL (gQTL), with just 2 collectively explaining 18% of the variance. We found little overlap between vQTL and gQTL, suggesting that variation in these larval traits is controlled by different genes. This study demonstrates the feasibility of genotyping single larvae for the identification of multiple QTL. Understanding genetic variation in larval biology is important for a comprehensive understanding of marine recruitment.

Unravelling the genetics of non-random fertilization associated with gametic incompatibility

In the dairy industry, mate allocation is dependent on the producer’s breeding goals and the parents’ breeding values. The probability of pregnancy differs among sire-dam combinations, and the compatibility of a pair may vary due to the combination of gametic haplotypes. Under the hypothesis that incomplete incompatibility would reduce the odds of fertilization, and complete incompatibility would lead to a non-fertilizing or lethal combination, deviation from Mendelian inheritance expectations would be observed for incompatible pairs. By adding an interaction to a transmission ratio distortion (TRD) model, which detects departure from the Mendelian expectations, genomic regions linked to gametic incompatibility can be identified. This study aimed to determine the genetic background of gametic incompatibility in Holstein cattle. A total of 283,817 genotyped Holstein trios were used in a TRD analysis, resulting in 422 significant regions, which contained 2075 positional genes further investigated for network, overrepresentation, and guilt-by-association analyses. The identified biological pathways were associated with immunology and cellular communication and a total of 16 functional candidate genes were identified. Further investigation of gametic incompatibility will provide opportunities to improve mate allocation for the dairy cattle industry.

Rüdin's 1916 Monograph: On the Inheritance and Primary Origin of Dementia Praecox.

In 1916, Ernst Rüdin published the first modern family study in the history of psychiatric genetics, the major goal of which was to test whether the pattern of risk in the siblings of dementia praecox (DP) probands followed Mendelian expectations. He utilized systematic ascertainment of probands and multisourced diagnostic assessments of probands and relatives, applying the narrow Kraepelinian concept of DP. In a novel step, he collaborated closely with a statistical geneticist-Wilhelm Weinberg-and applied his sibling, proband, and age correction methods. In his key sample-701 sibships when neither parent had DP-the morbid risk for DP in siblings was 4.48%, much lower than 25% expected for a recessive disorder. Risk for DP was increased by alcoholism or other mental disorders in parents. Other non-DP psychoses were common in both siblings and parents of DP probands. Rüdin discussed several alternative genetic models for DP including a 2-locus recessive, incomplete penetrance, and an oligogenic model. The high rates of other psychoses and psychopathic personalities in relatives might arise, he suggested, because these disorders shared genetic risks with DP. Rüdin established that DP, when carefully studied, ran in families, did not have a simple Mendelian genetic transmission pattern, and appeared likely to be genetically related to other non-DP psychotic disorders and perhaps some kinds of psychopathic personalities. This study, the most important in Rüdin's career, should be viewed in the context of his later extensive support of and collaboration with Nazi eugenic policies.

Abstract 1452: Analyses of whole exome sequencing (WES) data of hereditary lung cancer families identify germline copy number variations (CNVs) in multiple genes

Abstract Lung cancer (LC) is the most common cause of cancer mortality and the third most common cancer by incidence in the United States. While environmental factors play an important role in its development, LC risk also exhibits a high degree of heritability. Linkage analyses and genome-wide association studies have identified multiple loci associated with increased LC risk; however, much of the heritability has yet to be explained by these loci. Structural mutations, including copy number variations (CNVs), contribute to phenotypic diversity through dosage and/or cis-regulatory effects. Unbiased CNV mapping is only possible with the use of high-depth, short-read sequencing and remains much more complicated and prone to false positives than SNP detection. As the tools necessary for CNV detection have improved, both somatic and germline CNVs have been shown to play an important role in disease, especially cancer, and often they account for a significant proportion of pathogenic variants. Little has been done to understand the role of germline CNVs in the biological pathways of hereditary lung cancer (HLC). The goal of the current project is to utilize the whole exome sequencing (WES) data in identifying the CNVs in the HLC families (≥3 LC/family) recruited by the Genetic Epidemiology of Lung Cancer Consortium (GELCC). This work uses germline WES data from 203 individuals (60 with a LC diagnosis) from 25 HLC families (≥3 LC affected/family). We limited our investigation to CNVs called by two independent tools using read depth to infer copy number changes and genomic breakpoints: GATK 4 (https://gatk.broadinstitute.org) and XHMM (https://atgu.mgh.harvard.edu/xhmm/). We have identified CNVs (deletions) in the following protein coding genes: KIR2DL1 (19q13.42; OR=1.77), DMBT1 (10q26.13; OR=1.56), SIBPB1 (20p13; OR=1.53), LILRA6 (20p13; OR=1.53), and HLA-DRB5 (6p21.32; OR=1.64) in ≥3 families in at least two individuals/family. All of these genes with the exception of HLA-DRB5 were previously reported in LC studies; HLA-DRB5 was reported in other cancer studies. DMBT1 was reported to be a candidate tumor suppressor gene and frequent loss of heterozygosity (LOH) was observed in several human tumors. It is highly expressed in lung and loss of expression was reported in LC cell lines. All CNVs identified in our study are consistent with Mendelian expectations and appear to be uncommon in the general population. CNVs in these genes may contribute to the lung cancer risk in the HLC families. Further validation of the identified variants is ongoing. We will consider overall CNV burden and disease association with identified deletions and duplications. The enrichment of rare variants in oncogenically associated genes that co-segregate with LC provides specific mutations for future work and improves our understanding of the inheritance and pathogenesis of LC. Citation Format: John Waldron, Kirsten W. Termine, Anthony M. Musolf, Mariza de Andrade, Colette Gaba, Ramaswamy Govindan, Ping Yang, Ming You, Ellen Jaeger, Angelle F. Bencaz, Marshall W. Anderson, Ann G. Schwartz, Susan M. Pinney, Christopher I. Amos, Joan E. Bailey-Wilson, Diptasri M. Mandal. Analyses of whole exome sequencing (WES) data of hereditary lung cancer families identify germline copy number variations (CNVs) in multiple genes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1452.

31 Gametic Incompatibility: Improving the Success of Mate Allocation in Dairy Cattle

Abstract In the dairy industry, mate allocation is mainly based on the parents’ breeding values and inbreeding coefficients aiming to achieve the producer’s breeding goal. With artificial insemination, the portfolio of sires to choose from is large and the quality of the semen doses is standardized. However, not all sire-dam matings are equally likely to produce a successful pregnancy. Among other reproduction issues, the success of a mating could vary due to the incompatibility of gametes coming from the sire and the dam and could influence the fertilization’s success, additionally to the reproductive capacity of the parents. Considering the gametic incompatibility of the potential parents could be a novel option to improve mating plans. Under the hypothesis that gametic incompatibility has a significant effect on reproduction and reduces the odds of fertilization and pregnancy, this study aimed to determine the genetic background of gametic incompatibility. Transmission ratio distortion (TRD), which detects deviations from Mendelian inheritance expectations, is commonly used to identify deleterious mutations. We adapted the TRD model by including an interaction effect between the gametes leading to the offspring genotype to detect regions with TRD effects and gametic incompatibility. Our dataset contained 436,651 genotyped (50K SNP) Canadian Holstein cattle from 283,817 parents-offspring trios. A total of 482 regions with TRD containing 671 positional genes were found. The functional analysis detected biological pathways associated with uterus development, embryonic skeletal system development, and nervous system development. Additionally, gene ontology terms from the topology-based pathway enrichment analysis were mostly related to the steroid hormones signalling pathway. Although difficult, genes specific to gametic incompatibility could be differentiated from genes underlying other reproduction processes by refining the genetic regions with TRD. With further investigation, we will provide new information to improve mate allocation for the dairy cattle industry.

Unravelling the mystery of female meiotic drive: where we are.

Female meiotic drive is the phenomenon where a selfish genetic element alters chromosome segregation during female meiosis to segregate to the egg and transmit to the next generation more frequently than Mendelian expectation. While several examples of female meiotic drive have been known for many decades, a molecular understanding of the underlying mechanisms has been elusive. Recent advances in this area in several model species prompts a comparative re-examination of these drive systems. In this review, we compare female meiotic drive of several animal and plant species, highlighting pertinent similarities.

Magnitude of Mendelian versus complex inheritance of rare disorders.

In medical genetics, the vast majority of patients with a currently known genetic basis harbor a rare deleterious allele explaining its Mendelian inheritance. Increasingly, for these phenotypes, we recognize exceptions to Mendelian expectations from non-penetrance of clinical disease to significant inter-individual variation in clinical manifestations, likely reflecting the actions of additional modifier genes. Despite recent progress, we still remain ignorant about the molecular basis for many rare disorders presumed to be Mendelian. The molecular evidence increasingly suggests a role for multiple genes in some of these cases, but for how many? In this article, I discuss why equating a phenotype as Mendelian or complex may be short-sighted or even erroneous. As we learn more about the functions of the human genome with its genes in networks, we should view the phenotype of an individual patient as arising from his or her total genomic deleterious burden in a set of functionally inter-related genes affecting that phenotype. This can sometimes arise from deleterious allele(s) at a single gene (Mendelian inheritance) creating a specific biochemical deficiency (or excess) but could just as frequently arise from the cumulative effects of multiple disease alleles (complex inheritance) leading to the same biochemical deficiency (or excess).

Patterns and mechanisms of sex ratio distortion in the Collaborative Cross mouse mapping population.

In species with single-locus, chromosome-based mechanisms of sex determination, the laws of segregation predict an equal ratio of females to males at birth. Here, we show that departures from this Mendelian expectation are commonplace in the 8-way recombinant inbred Collaborative Cross (CC) mouse population. More than one-third of CC strains exhibit significant sex ratio distortion (SRD) at wean, with twice as many male-biased than female-biased strains. We show that these pervasive sex biases persist across multiple breeding environments, are stable over time, and are not mediated by random maternal effects. SRD exhibits a heritable component, but QTL mapping analyses fail to nominate any large effect loci. These findings, combined with the reported absence of sex ratio biases in the CC founder strains, suggest that SRD manifests from multilocus combinations of alleles only uncovered in recombined CC genomes. We explore several potential complex genetic mechanisms for SRD, including allelic interactions leading to sex-biased lethality, genetic sex reversal, chromosome drive mediated by sex-linked selfish elements, and incompatibilities between specific maternal and paternal genotypes. We show that no one mechanism offers a singular explanation for this population-wide SRD. Instead, our data present preliminary evidence for the action of distinct mechanisms of SRD at play in different strains. Taken together, our work exposes the pervasiveness of SRD in the CC population and nominates the CC as a powerful resource for investigating diverse genetic causes of biased sex chromosome transmission.

First evidence of deviation from Mendelian proportions in a conservation programme.

Classic Mendelian inheritance is the bedrock of population genetics and underpins pedigree-based management of animal populations. However, assumptions of Mendelian inheritance might not be upheld in conservation breeding programmes if early viability selection occurs, even when efforts are made to equalise genetic contributions of breeders. To test this possibility, we investigated deviations from Mendelian proportions in a captive metapopulation of the endangered Tasmanian devil. This marsupial population is ideal for addressing evolutionary questions in conservation due to its large size, range of enclosure types (varying in environmental conditions), good genomic resources (which aid interpretation), and the species' biology. Devil mothers give birth to more offspring than they can nurse in the pouch, providing the potential for intense viability selection amongst embryos. We used data from 140known sire-dam-offspring triads to isolate within-family selection from population-level mechanisms (such as mate choice or inbreeding), and compared observed offspring genotypes at 123 targeted SNPs to neutral (i.e., Mendelian) expectations. We found lower offspring heterozygosity than expected, and subtle patterns that varied across a gradient of management intensity from zoo-like enclosures to semi-wild environments for some loci. Meiotic drive or maternal-foetal incompatibilities are consistent with our results, although we cannot statistically confirm these mechanisms. We found some evidence that maternal genotype affects annual litter size, suggesting that family-level patterns are driven by differential offspring mortality before birth or during early development. Our results show that deviations from Mendelian inheritance can occur in conservation programmes, despite best-practice management to prevent selection.

A novel test for annexin A5 M2 haplotyping in in vitro fertilization patients and preimplantation embryos

To develop a test for evaluating the annexin A5 M2 haplotype in invitro fertilization patients and preimplantation embryos. Test performance was measured by comparing Sanger sequencing of parental blood DNA and quantitative real-time polymerase chain reaction (qPCR) of saliva DNA, 3 fibroblast cell line 7-cell aliquots and their corresponding purified DNA, 123 trophectoderm biopsy samples, and DNA isolated from 1 embryonic stem cell line along with the Mendelian inheritance expectations, embryo Sanger sequencing, and single-nucleotide polymorphism (SNP) microarray-based linkage analysis. Preimplantation genetic testing laboratory research on IVF patient and embryo DNA. An assay was developed for the detection of the M2 haplotype on saliva samples of 6 invitro fertilization patients. In addition, 13 patients who underwent preimplantation genetic testing with data on parental and embryo biopsy DNA available for research use were evaluated. None. The concordance rates between Sanger sequencing, SNP array-based linkage analysis, and Mendelian inheritance expectations with qPCR. The concordance rate between Sanger sequencing and qPCR was 100% on parental blood DNA and saliva DNA. The sample concordance rate between all replicates of 7-cell aliquots was 100%. The sample concordance rate between 3 cell lines used to prepare 7-cell aliquots and purified genomic DNA was 100%. The concordance rate between qPCR and Sanger sequencing results from a single trophectoderm biopsy and isolated embryonic stem cell line was 100%. The concordance rate of trophectoderm biopsy qPCR results and expectations from Mendelian inheritance rules was 97%; however, when SNP array-based linkage analysis was included, the concordance rate reached 100%. This study resulted in the development of a convenient saliva collection method and qPCR-based genotyping method to screen for the M2 haplotype. In addition, a novel method for testing preimplantation embryos has been established, providing an alternative to the use of low molecular weight heparin, through selection of embryos without the M2 haplotype.