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PubMed1998

In Situ Transmission Electron Microscopy Observations of Silicidation Processes for Cobalt Thin Films Deposited on Silicon.

: Morphological evolution associated with silicidation of Co thin films deposited on (100) and (111) Si substrates has been followed using transmission electron microscopy with in situ thermal annealing from ambient temperature up to 850 degreesC. Noticeable structural changes associated with the formation of CoSi2 occur at temperatures as low as 400 degreesC and the reaction is essentially complete at about 500 degreesC. Prolonged heating above 500 degreesC leads to CoSi2 grain growth and coalescence and, finally, to pinholes formation. Silicidation of Co films on (100) and (111) Si substrates follows the same pattern. The morphology of films annealed in situ is similar to those annealed ex situ except that the Si/CoSi2 interface appears to be much rougher. This behavior is associated with the specific geometry of cross-sectional TEM specimens, where surface diffusion dominates bulk diffusion. Very thin Co films, which have less contribution from surface diffusion than thicker films, are ideal for studying dynamic phenomena at Co/Si reactive interfaces.

Journal Article↗
PubMed2001

Fossil that fills a critical gap in avian evolution.

Despite the discoveries of well-preserved Mesozoic birds, a key part of avian evolution, close to the radiation of all living birds (Aves), remains poorly represented. Here we report on a new taxon from the Late Cretaceous locality of Ukhaa Tolgod, Mongolia, that offers insight into this critically unsampled period. Apsaravis and the controversial alvarezsaurids are the only avialan taxa known from the continental deposits at Ukhaa Tolgod, which have produced hundreds of fossil mammals, lizards and other small dinosaurs. The new taxon, Apsaravis ukhaana, is the best-preserved specimen of a Mesozoic ornithurine bird discovered in over a century. It provides data important for assessing morphological evolution across Avialae, with implications for, first, the monophyly of Enantiornithes and Sauriurae; second, the proposition that the Mesozoic sister taxa of extant birds, as part of an 'ecological bottleneck', inhabited exclusively near-shore and marine environments; and third, the evolution of flight after its origin.

Animals↗
PubMed2000

Evolutionary developmental biology and the problem of variation.

One of the oldest problems in evolutionary biology remains largely unsolved. Which mutations generate evolutionarily relevant phenotypic variation? What kinds of molecular changes do they entail? What are the phenotypic magnitudes, frequencies of origin, and pleiotropic effects of such mutations? How is the genome constructed to allow the observed abundance of phenotypic diversity? Historically, the neo-Darwinian synthesizers stressed the predominance of micromutations in evolution, whereas others noted the similarities between some dramatic mutations and evolutionary transitions to argue for macromutationism. Arguments on both sides have been biased by misconceptions of the developmental effects of mutations. For example, the traditional view that mutations of important developmental genes always have large pleiotropic effects can now be seen to be a conclusion drawn from observations of a small class of mutations with dramatic effects. It is possible that some mutations, for example, those in cis-regulatory DNA, have few or no pleiotropic effects and may be the predominant source of morphological evolution. In contrast, mutations causing dramatic phenotypic effects, although superficially similar to hypothesized evolutionary transitions, are unlikely to fairly represent the true path of evolution. Recent developmental studies of gene function provide a new way of conceptualizing and studying variation that contrasts with the traditional genetic view that was incorporated into neo-Darwinian theory and population genetics. This new approach in developmental biology is as important for microevolutionary studies as the actual results from recent evolutionary developmental studies. In particular, this approach will assist in the task of identifying the specific mutations generating phenotypic variation and elucidating how they alter gene function. These data will provide the current missing link between molecular and phenotypic variation in natural populations.

Animals↗
PubMed1997

The role of habitat shift in the evolution of lizard morphology: evidence from tropical Tropidurus.

We compared morphology of two geographically close populations of the tropical lizard Tropidurus hispidus to test the hypothesis that habitat structure influences the evolution of morphology and ecology at the population level. T. hispidus isolated on a rock outcrop surrounded by tropical forest use rock crevices for refuge and appear dorsoventrally compressed compared with those in open savanna. A principal components analysis revealed that the populations were differentially distributed along an axis representing primarily three components of shape: body width, body height, and hind-leg length. Morphological divergence was supported by a principal components analysis of size-free morphological variables. Mitochondrial DNA sequences of ATPase 6 indicate that these populations are closely related relative to other T. hispidus, the rock outcrop morphology and ecology are derived within T. hispidus, and morphological and ecological divergence has occurred more rapidly than genetic divergence. This suggests that natural selection can rapidly adjust morphology and ecology in response to a recent history of exposure to habitats differing in structure, a result heretofore implied from comparative studies among lizard species.

Animals↗
PubMed1995

Observations on the pathological spectrum and clinical course of microsporidiosis in men infected with the human immunodeficiency virus: follow-up study.

The purposes of this research were to determine whether microsporidian infection is accompanied by structural alterations of the duodenal mucosa and to characterize the clinical and morphological evolution of intestinal microsporidiosis. In a previous systematic electron microscopic evaluation of mucosal biopsy specimens from patients with human immunodeficiency virus infection, we detected Enterocytozoon bieneusi in the duodenal tissue of 31 men. This report concerns a follow-up study of these 31 men, who underwent repeated clinical and laboratory evaluations, including repeated duodenal biopsies. Eighteen men had chronic diarrhea at enrollment and 13 had no diarrhea. The CD4+ cell counts (per mm3) ranged from 10 to 660 and were normal for three men. E. bieneusi infection was accompanied by a wide spectrum of histopathology of duodenal tissue; over a mean follow-up of 15 months, no consistent change in duodenal mucosal morphology was observed, and diarrhea did not invariably develop. These observations indicate that diarrhea and severe villus injury do not invariably accompany infection. Further studies are needed to determine the relationship between E. bieneusi infection and clinical illness.

AIDS-Related Opportunistic Infections↗
PubMed1986

Morphological differentiation of mitochondria in the early chick embryo: a stereological analysis.

The morphological evolution of mitochondria in three cell types of chick embryo in neurulation was analyzed by stereological methods. Mitochondria, showing a random distribution, were characterized by moderate electron-dense matrices and normal cristae. The numerical density of mitochondria significantly increased in the neuroectoderm and epiblastic cells while their volume density remained unchanged. The mitochondria in mesoderm cells were ellipsoidal (axial ratio 2:1) at stages 5 and 8 although they underwent an elongation in neuroectoderm and epiblastic cells (axial ratio from 2:1 to 1.6:1). The individual size of "average mitochondria" in the mesoderm cells was smaller than in other cell types. The total V/S (volume/surface) ratio of mitochondria decreased during neurulation. These morphological changes have been discussed emphasizing the possible metabolical role of mitochondria during morphogenesis.

Animals↗
PubMed2003

Perspective: embedded molecular switches, anticancer selection, and effects on ontogenetic rates: a hypothesis of developmental constraint on morphogenesis and evolution.

The switch between the cell cycle and the progress of differentiation in developmental pathways is prevalent throughout the eukaryotes in all major cell lineages. Disruptions to the molecular signals regulating the switch between proliferative and differentiating states are severe, often resulting in cancer formation (uncontrolled proliferation) or major developmental disorders. Uncontrolled proliferation and developmental disorders are potentially lethal defects in the developing animal. Therefore, natural selection would likely favor a tightly controlled regulatory mechanism to help prevent these fundamental defects. Although selection is usually thought of as a consequence of environmental or ecological influences, in this case the selective force to maintain this molecular switch is internal, manifested as a potentially lethal developmental defect. The morphogenetic consequences of this prevalent, deeply embedded, and tightly controlled mechanistic switch are currently unexplored, however experimental and correlative evidence from several sources suggest that there are important consequences on the control of growth rates and developmental rates in organs and in the whole animal. These observations lead one to consider the possibility of a developmental constraint on ontogenetic rates and morphological evolution maintained by natural selection against cancer and other embryonic lethal defects.

Biological Evolution↗
PubMedDate not supplied

Transient hepatic attenuation differences (THAD) not connected to focal lesions.

PURPOSE: To report our experience with helical CT evaluation of transient hepatic attenuation differences (THAD), and in particular of those not associated with focal lesions, in an attempt to provide an aetiopathogenetic picture that accounts for the morphology, evolution and density of THAD. MATERIALS AND METHODS: Between January 1998 and January 2001 we observed THAD in 130/988 biphasic helical CT liver examinations performed in the arterial and portal dominant phase. THAD were associated to focal hepatic lesions in 87 patients; in 43 patients there was no such association. This second group of patients, composed of 23 males and 20 females ranging in age from 17 to 80 years (average = 58.8), was enrolled in the study. THAD were associated to: Budd-Chiari syndrome (9), portal venous thrombosis (10), liver cirrhosis (7), acute inflammation of an adjacent organ (4), dilatation of the entire biliary tree (3), hepatic stasis caused by heart failure (2) and constrictive pericarditis (1), fine-needle percutaneous biopsy (2), arterioportal shunting (2), parenchymal compression by fractured ribs (2) and by a strengthened phrenic pillar (1). THAD were evaluated according to extension, morphology and density. For each case at least 10 density measurements were performed by sampling regions of interest on the parenchyma with THAD and on the contralateral parenchyma. The results (mean and standard deviation) were compared to those relative to 30 healthy patients. 22/43 patients were followed up for 6#150;24 months by at least one US and helical CT examination. During CT, the direct appreciation of vascular thrombus during the portal dominant phase was also considered. RESULTS: We detected 18 localised and 25 diffuse THAD. The localised sectoral THAD (11), wedge-shaped with clear border sign, were associated to thrombosis of a portal branch (6), fine-needle percutaneous biopsy (2), arterioportal shunting (2) and partial Budd-Chiari syndrome (1). The localised non-sectoral THAD (7), with variable morphology and without the clear border sign, were associated to acute inflammation of an adjacent organ (4) and to parenchymal compression by the ribs or diaphragm (3). Diffuse THAD associated to Budd-Chiari syndrome (8) and to heart failure (3) showed mosaic enhancement of hepatic parenchyma (patchy pattern); those linked to portal trunk thrombosis (4) and cirrhosis (7) revealed predominant enhancement of external hepatic parenchyma (central-peripheral phenomenon); finally, those concurrent with dilatation of the entire biliary tree showed parenchymal enhancement close to the dilated bile ducts (peribiliary pattern). Follow-up (22/43) demonstrated complete THAD regression after removal (5/22) and less conspicuity of THAD after partial overcome of the stoppage (1/22). In 2/22 cases of arterioportal shunting no substantial changes were seen. The remaining 14/22 cases showed a gradual, slow tendency towards THAD regression with hypotrophy of the involved parenchyma and compensatory contralateral hypertrophy even in the case of endurance of the causative agents. CONCLUSIONS: Based on our experience and the literature we suggest a classification for THAD unrelated to focal hepatic lesions. We recognise 4 causes: portal vein stoppage-obstruction, portal in-flow diversion, trauma and inflammation. When THAD is related to the first three causes pathogenesis is portal hypoperfusion. In the fourth group the mediators of the arterial phenomena are those of inflammation even though portal hypoperfusion might be involved as well. THAD identification makes the detection of vascular thrombi easier by comparison with their direct finding during the portal dominant phase. Finally, THAD are to be investigated for their potential utility in the detection and characterisation of several hepatic diseases. As a consequence, hepatic CT studies cannot ignore arterial dominant phase evaluation, even if no focal hepatic lesions are expected.

Adolescent↗
PubMed1998

The natural history of the cervical foramen in symptomatic and asymptomatic individuals aged 20-60 years as measured by magnetic resonance imaging. A descriptive approach.

STUDY DESIGN: This study was intended to identify normal degenerative morphologic evolution in the bony foramen in asymptomatic subjects by decade in comparison with symptomatic subjects of like decades. OBJECTIVES: To determine normal degenerative changes in the cervical spine caused by the aging process that predispose a person to foraminal stenosis and radiculopathy. SUMMARY OF BACKGROUND DATA: Cervical radiculopathy is a common problem caused by degenerative changes as people age. The characteristics of the foramen that result in stenosis are not known. METHODS: Five to six symptomatic and asymptomatic people in each decade volunteered for magnetic resonance imaging. Lordosis, disc heights, and ratio of spinal cord diameter to spinal canal diameter were measured at C4-C5, C5-C6, and C6-C7 from sagittal magnetic resonance images. Foraminal heights, widths, and areas were measured at the isthmus of the same foramen from oblique images. RESULTS: Foraminal heights, widths, and areas were larger in asymptomatic patients than in symptomatic patients. Morphologic analysis showed that inferior facet hypertrophy tended to decrease the width of the foramen in aging people. Disc heights, lordosis, and ratio of spinal cord diameter to spinal canal diameter showed no significant differences. CONCLUSIONS: Foraminal height affects overall foraminal area but tends to change little with age. Width also affects overall area and not only decreases in older people but also significantly affects the available area for the exiting nerve root.

Adult↗
PubMed1997

The influence of senescence on craniofacial and cervical morphology in humans.

This study discusses the morphologic evolution of the cranio-facial and cervical bone structures throughout life. A cephalometric study was made on lateral radiographs. The population studied included 84 males and 102 females. Ages ranged from 21 to 101. The cranial structures, superior facial structure, mandible and cervical vertebral column were successively examined. The anteroposterior diameter of the calvarium does not seem to undergo any modification during life. On the other hand, a highly significant increase of the thickness of this structure can be noted. The upper facial structure presents some modification, namely a significant increase of its posterior height. The palatine processus seems to change direction and pivot downwards and forwards. The maxillary sinus does not undergo any changes. The mandible, which is stable in its major axes, shows more malleable sectors which are more especially situated at the level of its body. The study of the cervical vertebral column reveals a loss of overall height, and an increase in the lordosis. The most numerous and most evident morphologic modifications were observed around the age of fifty in both males and females. The fact that these transformations are always commoned and greater in the latter reveals the plausible influence of the menopause. It appears that bone structures of membranous origin are the site of significant modifications compared with structures of endochondral origin, which benefit from a greater stability.

Adult↗
PubMed1998

Evolution of the "classical" cadherin family of cell adhesion molecules in vertebrates.

The cadherins are major mediators of calcium-dependent cell-cell adhesion and are also involved in cell signaling pathways during development. The classical cadherins, which are the definitive group of the cadherin superfamily, are transmembrane proteins that consist of an extracellular domain of five cadherin repeats, including an HAV tripeptide conserved in one binding surface within the first domain, and a highly conserved cytoplasmic domain that interacts with the actin cytoskeleton via the catenin proteins. These cadherins play major roles in vertebrate morphogenesis; they are expressed widely throughout development, antibodies to specific cadherins perturb a variety of developmental processes, and many gene knockouts are lethal at early stages of development. Phylogenetic analysis of the "classical" cadherins shows that in the vertebrates there are four paralog families. The rate of evolutionary change is radically different between the different paralogs, indicating that there are significantly different selection pressures on the functions of the various cadherins, both between the different paralogs in a single organism lineage and between different organism lineages within a single paralog family. There is also evidence for gene conversion between the E-cadherin and P-cadherin paralogs in Gallus gallus and possibly Xenopus laevis, but not between the same paralogs in the mammalian lineages. A scheme for the origin of the paralogs within the vertebrate lineage based on these analyses indicates that the presence of the four paralog families is a characteristic of vertebrates and that variation of cadherin structure and function is a significant factor in morphological evolution of vertebrates.

Animals↗
PubMed2002

The evolution of embryo size in angiosperms and other seed plants: implications for the evolution of seed dormancy.

Seed dormancy plays an important role in germination ecology and seed plant evolution. Morphological seed dormancy is caused by an underdeveloped embryo that must mature prior to germination. It has been suggested that the presence of an underdeveloped embryo is plesiomorphic among seed plants and that parallel directional change in embryo morphology has occurred separately in gymnosperms and in angiosperms. We test these hypotheses using original data on embryo morphology of key basal taxa, a published dataset, and the generalized least squares (GLS) method of ancestral character state reconstruction. Reconstructions for embryo to seed ratio (E:S) using family means for 179 families showed that E:S has increased between the ancestral angiosperm and almost all extant angiosperm taxa. Species in the rosid clade have particularly large embryos relative to the angiosperm ancestor. Results for the gymnosperms show a similar but smaller increase. There were no statistically significant differences in E:S between basal taxa and any derived group due to extremely large standard errors produced by GLS models. However, differences between reconstructed values for the angiosperm ancestor and more highly nested nodes are large and these results are robust to topological and branch-length manipulations. Our analysis supports the idea that the underdeveloped embryo is primitive among seed plants and that there has been a directional change in E:S within both angiosperms and gymnosperms. Our analysis suggests that dormancy enforced by an underdeveloped embryo is plesiomorphic among angiosperms and that nondormancy and other dormancy types probably evolved within the angiosperms. The shift in E:S was likely a heterochronic change, and has important implications for the life history of seed plants.

Biological Evolution↗
PubMed1999

Myocardial scarring after transmyocardial laser revascularization: A potential mechanism of clinical improvement?

BACKGROUND AND OBJECTIVE: The morphological evolution of transmyocardial laser channels was analyzed in a pig model. MATERIALS AND METHODS: Five channels were created in the lateral wall of the left ventricle of 12 animals, using a Ho:YAG laser. In half of the animals, an additional infarction was induced in the same area. Animals were sacrificed at one-week intervals until week 5 and the critical regions of the left ventricular wall were subjected to microscopic computed morphometrical analysis. RESULTS: There was no clearly patent lumen at any stage. Cross-sectional area of the channels fell from 8.5 +/- 1.2 mm(2) at day 0 to 2.1 +/- 0.1 mm(2) at day 35. From day 7 onward, the channel area was gradually replaced by granulation tissue and the proportion of the channel occupied by granulation scar tissue increased from 37 +/- 2% at day 7 to 100% at day 28. In the subgroup with concomitant infarction, granulation tissue of both channel and infarction became indistinguishable from day 14 onward. CONCLUSIONS: These results suggest strongly that channel patency is not the mechanism of angina relief after transmyocardial laser revascularization with Ho:YAG laser.

Animals↗
PubMed1998

Extra-tumoral breast tissue in breast-cancer patients: variations with a family history of breast cancer. WHO Collaborative Study of Neoplasia and Steroid Contraceptives.

In order to study the relationship between benign breast changes, a family history of breast cancer and breast cancer, extratumoral breast tissue from 1259 breast-cancer patients in the WHO Collaborative Study of Neoplasia and Contraceptives was classified histologically. The occurrence of ductal hyperplasia, ductal atypia, sclerosing adenosis, adenosis, lobular atypia, lactational metaplasia, cysts, apocrine metaplasia, apocrine hyperplasia and atypia, duct ectasia and the epithelial-stromal ratio was evaluated as absent, mild, moderate or marked, along with registration of the quality and number of slides. Information on occurrence of cancer in the family was available for patients' mothers and grandmothers. Logistic-regression analyses showed that the prevalence odds ratios for lactational metaplasia, cysts, duct ectasia and calcification were significantly increased in patients with a family history of breast cancer. Apocrine metaplasia and hyperplasia were not significantly increased. The prevalence rates of ductal atypia (ductal carcinoma in situ and atypical ductal hyperplasia), ductal hyperplasia, sclerosing adenosis, adenosis and high epithelial-stromal ratio did not differ significantly among patients with or without a family history of breast cancer. A family history of other types of cancer did not influence the occurrence of any of the benign components. The findings in the present study are strikingly similar to those in our earlier comparison of extra-tumoral breast tissue in patients from countries with high and low risk of breast cancer. It is reasonable to conclude from this that a history of breast cancer in a woman's mother or grandmother and the factors leading to higher risk of breast cancer in some countries than in others have similar effects on the morphologic evolution of breast cancer through benign and pre-cancerous changes.

Breast Diseases↗
PubMed1999

Description of the chondrocranium and osteogenesis of the Chacoan burrowing frog, Chacophrys pierotti (Anura: Leptodactylidae).

The larval chondrocranium of the large-headed leptodactylid frog, Chacophrys pierotti (Ceratophryinae), is described in detail. Descriptions include the ontogeny of the chondrocranium and osteogenesis of the cranial skeleton. The chondrocranium of C. pierotti is profoundly different from the chondrocrania previously described for the other genera of the Ceratophryinae (Ceratophrys and Lepidobatrachus). The chondrocranium of Chacophrys is longer than wide and not particularly robust or laterally expanded; that of Ceratophrys is very robust, whereas the chondrocranium of Lepidobatrachus is widely expanded laterally. These differences are particularly apparent in the elements associated with the jaw (i.e., suprarostral, infrarostral, Meckel's cartilage, palatoquadrate, cornua trabeculae), which are robust in Ceratophrys and thin and elongate in Lepidobatrachus. Unlike Ceratophrys and Lepidobatrachus, which possess highly specialized carnivorous larva, the chondrocranium of Chacophrys more closely resembles the typical microphagous herbivore morphology characteristic of other leptodactylid frogs for which the chondrocrania are known. These data suggest that Chacophrys is the basal taxon within the monophyletic Ceratophryinae. The ontogeny of the chondrocranium of Chacophrys, as well as the cranial ossification sequence, do not differ greatly from those described for Ceratophrys. Detailed descriptions of the ontogeny of the chondrocranium and the bony skeleton are needed for additional taxa within the Ceratophryinae (especially Lepidobatrachus). Such descriptive ontogenetic studies promise new insight into the phylogeny and morphological evolution of this remarkable group of large-headed frogs.

Animals↗
PubMed1985

Alzheimer changes in nondemented patients younger than sixty-five: possible early stages of Alzheimer's disease and senile dementia of Alzheimer type.

Senile plaques (SP) and neurofibrillary tangles (NFT) were found in 38 (74.5%) of 51 unselected brains of nondemented patients who died between the ages of 55 and 64 years. A high proportion (22, or 43%) had only NFTs. These were consistently present in the entorhinal cortex and/or the hippocampus; the olfactory bulb, the amygdala, and the nucleus basalis of Meynert were also occasionally involved. Isolated SPs were seen in only 3 brains (6%); SPs and NFTs coexisted in 13 (25.5%). The distribution patterns of NFTs and SPs differed. NFTs were seen in discrete, mostly single neurons of the structure, already noted, whereas SPs occurred in a more generalized distribution over the base and convexity of the cerebrum. The plaques were usually small (30 mu in diameter) and consisted of delicate fibrillary material. Other types of SP were also seen. The incidence of various types of plaques in nondemented patients is considered to indicate a morphological evolution of these structures.

Alzheimer Disease↗
PubMed2001

Comparative insect developmental genetics: phenotypes without mutants.

The last decade has seen a dramatic increase in interest in the extent to which morphological evolution depends on changes in regulatory pathways. Insects provide a fertile ground for study because of their diversity and our high level of understanding of the genetic regulation of development in Drosophila melanogaster. However, comparable genetic approaches are presently possible in only a small number of non-Drosophilid insects. In a recent paper, Hughes and Kaufman have used a new methodology, RNA interference, in the milkweed bug, Oncopeltus fasciatus, to phenocopy the effects of mutations in Hox genes. RNA interference involves the injection of double-stranded RNA of the same sequence as the relevant mRNA resulting in a depletion of that transcript. Hughes and Kaufman focused on the gnathal segments, which elaborate specialized appendages important to feeding. Their results indicate that gnathal adaptations in this bug are correlated with changes in Hox gene functions and interactions.

Animals↗
PubMed1994

Homeotic gene expression in the locust Schistocerca: an antibody that detects conserved epitopes in Ultrabithorax and abdominal-A proteins.

To investigate what role homeotic genes may play in morphological evolution, we are comparing homeotic gene expression in two very different insects, Drosophila (Diptera) and Schistocerca (Orthoptera). In this paper we describe a monoclonal antibody, FP6.87, that recognizes the products of both the Ultrabithorax (Ubx) and abdominal-A (abd-A) genes in Drosophila, via an epitope common to the carboxy terminal region of these two proteins. This antibody recognizes nuclear antigens present in the posterior thorax and abdomen of Schistocerca. We infer that it recognizes the Schistocerca homolog of UBX protein, and probably also of ABD-A. As the distribution of Schistocerca ABD-A protein is already known, we can use this reagent to map the expression of Schistocerca UBX in the thorax and anterior abdomen, where ABD-A is not expressed. Both the general domain, and many of the details, of UBX expression are remarkably conserved compared with Drosophila. Thus UBX expression extends back from T2 in the ectoderm (including the CNS), but only from A1 in the mesoderm. As noted for other bithorax complex genes in Schistocerca, expression begins in the abdomen, at or shortly before the time of segmentation. It only later spreads anteriorly to the thorax. For much of embryogenesis, the expression of UBX in the thoracic epidermis is largely restricted to the T3 limb. In this limb, UBX is strikingly regulated, in a complex pattern that reflects limb segmentation. Reviewing these and earlier observations, we conclude that evolutionary changes affect both the precise regulation of homeotic genes within segments, and probably also the spectrum of downstream genes that respond to homeotic gene expression in a given tissue. Overall domains of homeotic gene expression appear to be well conserved between different insect groups, though a change in the extent and timing of homeotic gene expression may underlie the modification of the posterior abdomen in different insect groups.

Amino Acid Sequence↗