PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 11440823

Mechanisms for differences in monozygous twins.

P Gringras·W Chen
View original source ↗Export metadata ↓

Abstract

Monozygous (MZ) twins are often described as being physically and genetically identical. Clinical determination of zygosity relies on the assumption that any physical differences between a pair of twins imply they are dizygous. Most twin research relies on the assumption that dizygous twins share approximately 50% of the same genes, whereas monozygous twins share 100%. There is, however, increasing evidence to challenge both these assumptions. In this review, we describe a number of intrauterine effects and genetic mechanisms that may result in phenotypic, genotypic, and epigenetic differences between monozygous twins. Newer molecular techniques are resulting in such differences being increasingly commonly recognised. The potential for differences in monozygotic twin pairs is an important consideration for both clinicians and researchers involved in twin work.

Explore related subjects

Genetic VariationGenotypeHumansPhenotypeTwins, MonozygoticJournal ArticleReviewTwin Study

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

P Gringras, W Chen. 2001. Mechanisms for differences in monozygous twins.. https://doi.org/10.1016/s0378-3782(01)00171-2

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2026

Mitochondrial genome-derived microsatellites reveal genetic diversity and population structure in Callery pear populations.

Callery pear (Pyrus calleryana Decne.; PC) possesses many desirable characteristics valued in managed landscapes. This has driven the release of numerous cultivars, including both hybrids and selections derived from native populations. The extensive planting of PC cultivars in managed areas has contributed to the widespread occurrence of invasive individuals across a broad range of habitats in the eastern United States (US). Self-incompatibility, tolerance to various environmental conditions, pathogen and pest resistance, intraspecific hybridization among the cultivars, possible interspecific hybridization with other Pyrus species, and seed dispersal by various vertebrates have contributed to the spread and persistence of PC across diverse environments. Because effective and environmentally appropriate management options remain limited, improved understanding of PC genetics may help inform management strategies. Previous studies have characterized PC diversity using nuclear genomic short sequence repeats (gSSRs), however, neither a mitochondrial genome resource nor mitochondrial short sequence repeats (mtSSRs) have been developed for this purpose. Here, we assembled a mitochondrial genome of 485,892 bp and used five mtSSRs to characterize mitochondrial diversity and population structure among accessions from the species' native range in Asia (n = 72), southeastern US escapees (SNesc; n = 90), Tennessee escapees (TNesc; n = 90), and US-released commercial cultivars (UScult; n = 69 representing 14 unique cultivars). We found a high genetic diversity (He = 0.728) and evidence of genetic structure in PC. In distance-based and multivariate analyses, UScult occupied an intermediate position between the Asian populations and the US escapees. The observed mitochondrial diversity among samples assigned to PC cultivars is consistent with a complex genetic landscape and may reflect distinct maternal lineages, cultivar-labeling or record-keeping discrepancies, and/or technical variation. This study underscores the need for broader genomic investigations using authenticated cultivar reference material and high-resolution nuclear markers to resolve cultivar ancestry, validate true-to-name identity, and inform species management.

Genetic Variation↗
PubMed2026

Molecular identification and diversity assessment of Tyrrhenian Romulea species (Iridaceae).

Taxonomic assignments based only on morphology are often insufficient for delimiting species, particularly in complexes shaped by hybridization and polyploidy, where species boundaries are unclear. This limitation hinders progress in ecological, biogeographic and conservation research. The genus Romulea, distributed across Africa and the Mediterranean Basin, exemplifies this challenge. Despite its remarkable diversity, Mediterranean Romulea has not received much attention from genetic and molecular studies. Here, we present the first multilocus genotype analysis of Mediterranean Romulea taxa, focusing on the Tyrrhenian biogeographic province. Using target-capture sequencing with the universal Angiosperms353 kit, we generated genomic data for 272 individuals representing 18 putative taxa. Our findings reveal genetic groups that align with current taxonomy, the existence of cryptic divergence, and highlight the role of hybridization. Furthermore, analysis of intra-individual genetic diversity suggests one or several allopolyploid origins for Mediterranean Romulea. Four taxa (R. assumptionis, R. revelieri, R. ligustica, R. rollii) are consistently well differentiated across nuclear and plastid datasets, supporting their recognition as distinct species. In contrast, the widespread species R. ramiflora and R. columnae contain well-differentiated groups that may represent cryptic speciation. Several other taxa, including R. x melitensis, R. corsica, and R. bulbocodium, exhibit genomic signatures consistent with hybrid origins. Plastid and nuclear variation patterns are consistent with a hypothesis of rapid radiation in the Tyrrhenian region. These results provide a primary genomic framework for the integrative taxonomy of Romulea.

Genetic Variation↗
PubMed2025

Exploration of the genetic diversity of Avena Fatua L. (wild oat) through genotyping-by-sequencing and SDS-PAGE.

BACKGROUND: The consumption of oats has rapidly increased due to their exceptional nutritional value. However, concerns over genetic erosion have emerged as oat breeding programs rely on a highly limited genetic pool. This study aimed to expand the genetic diversity pool of oats by collecting wild oat (Avena fatua L.) populations in South Korea and assessing their genetic diversity and seed storage protein patterns. RESULTS: A total of 237 A. fatua individuals were collected in 2022 from eight regions in the southwestern coastal areas of South Korea. Genetic diversity and seed storage protein patterns were analyzed using genotyping-by-sequencing (GBS) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The GBS analysis identified 20,836 single-nucleotide polymorphisms (SNPs). An analysis of molecular variance (AMOVA) based on regional populations revealed that 40.9% of the genetic variation was attributed to differences among populations, while 59.1% was within populations, indicating high genetic differentiation within regional populations. Subsequent population structure analysis and discriminant analysis of principal components (DAPC) both stated the formation of two distinct genetic groups, with an AMOVA value of 70.9% between the groups, suggesting a high level of genetic variation. Pairwise FST analysis was conducted to compare the genetic differentiation between two populations, revealing that Jindo and Jangheung exhibited the highest level of genetic differentiation (FST = 0.795) among the geographic groups. Seed storage proteins were analyzed using SDS-PAGE, and the patterns were grouped using k-means clustering. A comparison between the groups based on protein patterns and those based on genetic variation revealed no significant correlation. CONCLUSION: This study provides data on the genetic diversity of A. fatua, a wild relative of cultivated oats, aimed at expanding the genetic pool of oats for future breeding programs. These findings are expected to be a foundational resource for oat breeding and genetic improvement efforts.

Genetic Variation↗