The Making of a Flight Feather: Bio-architectural Principles and Adaptation.

The evolution of flight in feathered dinosaurs and early birds over millions of years required flight feathers whose architecture features hierarchical branches. While barb-based feather forms were investigated, feather shafts and vanes are understudied. Here, we take a multi-disciplinary approach to study their molecular control and bio-architectural organizations. In rachidial ridges, epidermal progenitors generate cortex and medullary keratinocytes, guided by Bmp and transforming growth factor ß (TGF-ß) signaling that convert rachides into adaptable bilayer composite beams. In barb ridges, epidermal progenitors generate cylindrical, plate-, or hooklet-shaped barbule cells that form fluffy branches or pennaceous vanes, mediated by asymmetric cell junction and keratin expression. Transcriptome analyses and functional studies show anterior-posterior Wnt2b signaling within the dermal papilla controls barbule cell fates with spatiotemporal collinearity. Quantitative bio-physical analyses of feathers from birds with different flight characteristics and feathers in Burmese amber reveal how multi-dimensional functionality can be achieved and may inspire future composite material designs. VIDEO ABSTRACT.

Chicken HOXC8 and HOXC10 genes may play a role in the altered skull morphology associated with the Crest phenotype.

One of the most intriguing traits found in domestic chickens is the Crest phenotype. This trait, characterized by a tuft of elongated feathers sprouted from the head, is found in breeds such as Polish chickens and Silkie chickens. Moreover, some crested chicken breeds also exhibit a protuberance in their anterodorsal skull region. Previous studies have strived to identify the causative factors of this trait. This study aimed to elucidate the role of chicken HOXC8 and HOXC10 in the formation of the Crest phenotype. We explored the effect of ectopic expression of HOXC8 or HOXC10 on the chicken craniofacial morphology using the RCAS retrovirus transformation system. Microcomputed tomography scanning was conducted to measure the 3D structure of the cranial bone of transgenic embryos for geometric morphometric analysis. We found that the ectopic expression of HOXC8 or HOXC10 in chicken heads caused mild morphological changes in the skull compared with the GFP-transgenic control group. Geometric morphometric analysis showed that HOXC8 and HOXC10 transgenic groups expressed a mild upward shape change in the frontal region of the skull compared with the control group, which is similar to what is seen in the crested chicken breeds. In conclusion, this study supports findings in previous studies in which HOX genes play a role in the formation of the altered skull morphology related to the Crest phenotype. It also supports that mutations in HOX genes may contribute to intra- and inter-specific variation in morphological traits in vertebrates.

Single-nucleotide polymorphisms in genes related to oxidative stress and ion channels in chickens are associated with semen quality and hormonal responses to thermal stress.

Heat stress causes economic loss of livestock industry in tropical areas. Exploring genetic markers for selection of thermotolerance will benefit chicken production. Oxidative stress and fluid-salt balance are tightly associated with thermotolerance and productivity in domestic animals. The study aimed to identify single-nucleotide polymorphisms (SNPs) in genes related to oxidative stress and ion-channel regulation and their associations with semen quality and hormonal responses. In total, 28 SNPs within 11 candidate genes were identified to associate with hormonal changes and semen quality in both broiler- and layer-type Taiwan country chickens (TCCs) after exposure to acute heat stress at 38 °C for 4 h. Acute heat stress significantly affected plasma levels of triiodothyronine and corticosterone and reduced sperm motility, viability, and concentrations in both strains at Day 1 after exposure. In the B-strain TCCs, five SNPs within NDUFA8 and DAB2IP had significant effects on plasma adrenaline and corticosterone levels, and six SNPs within TRPC1, SLC9A9, and TRPC7 markedly affected plasma corticosterone and triiodothyronine levels. In the L2 strain, 15 SNPs within PSMA2, TPK1, MTF1, and CUL1 exerted effects on plasma corticosterone and triiodothyronine levels. Five SNPs within CUL3, TRPC1, and SLC9A9 in the B strain and two SNPs within MTF1 in the L2 strain were associated with sperm concentrations at Day 1 after exposure to heat stress. In conclusion, acute heat stress impaired semen quality and altered plasma corticosterone and triiodothyronine levels in TCCs. Some SNPs involved in oxidative stress and ion-channel regulation were identified to associate with the hormonal and semen alterations. These SNPs in conjunction with differential hormonal responses and semen quality serve as genetic markers for thermotolerance selection in sire lines of chickens.

Unraveling the history of the genus Gallus through whole genome sequencing.

The genus Gallus is distributed across a large part of Southeast Asia and has received special interest because the domestic chicken, Gallus gallus domesticus, has spread all over the world and is a major protein source for humans. There are four species: the red junglefowl (G. gallus), the green junglefowl (G. varius), the Lafayette's junglefowl (G. lafayettii) and the grey junglefowl (G. sonneratii). The aim of this study is to reconstruct the history of these species by a whole genome sequencing approach and resolve inconsistencies between well supported topologies inferred using different data and methods. Using deep sequencing, we identified over 35 million SNPs and reconstructed the phylogeny of the Gallus genus using both distance (BioNJ) and maximum likelihood (ML) methods. We observed discrepancies according to reconstruction methods and genomic components. The two most supported topologies were previously reported and were discriminated by using phylogenetic and gene flow analyses, based on ABBA statistics. Terminology fix requested by the deputy editor led to support a scenario with G. gallus as the earliest branching lineage of the Gallus genus, instead of G. varius. We discuss the probable causes for the discrepancy. A likely one is that G. sonneratii samples from parks or private collections are all recent hybrids, with roughly 10% of their autosomal genome originating from G. gallus. The removal of those regions is needed to provide reliable data, which was not done in previous studies. We took care of this and additionally included two wild G. sonneratii samples from India, showing no trace of introgression. This reinforces the importance of carefully selecting and validating samples and genomic components in phylogenomics.

Dynamic contrast-enhanced magnetic resonance imaging in correlation with tongue cancer stages.

BACKGROUND: Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) plays a significant role in tumor stage as it can be used to measure tissue perfusion and permeability of tumors. PURPOSE: To investigate the relationships between both quantitative and semi-quantitative variables obtained from DCE-MRI and tongue cancer stages. MATERIAL AND METHODS: Mean values of Ktrans, enhancement ratio (ER), wash-in slope (slope), and the 95th percentile (95%) values of the distribution for Ktrans, ER, and slope values (Ktrans (95%), ER (95%), and slope (95%), respectively) were calculated for 53 patients with tongue cancers (American Joint Committee on Cancer 8th Edition stage group: 10 in stages I and II, 14 in stage III, 21 in stage IVa, and eight in stage IVb as determined by histopathologic assessment). The relationship between tumor staging and each of the six DCE-MRI parameters was assessed separately using ordinal logistic regression. RESULTS: The logistic regression analysis revealed that both mean and 95th percentile values of Ktrans were significantly and positively correlated with tongue cancer stage (P < 0.01). More aggressive tumor stages had larger kinetic parameter. Moreover, the semi-quantitative parameters, such as ER (95%) and slope (95%), may be more significant predictors for evaluating tongue cancer stages than the mean ER and mean slope. CONCLUSION: Both quantitative and semi-quantitative imaging biomarkers are useful for evaluating the stages of tongue cancer, and the indices obtained from DCE-MRI were positively correlated with the tumor stages. These parameters have the potential to non-invasively evaluate the stages of tongue cancer in the clinical setting.

Distribution and environmental risk assessment of trace metals in sludge from multiple sources in Taiwan.

This study evaluated the level of the contaminant of the heavy metals in sludge from different sources and the ecological risk criteria associated with it was also analyzed to establish its reuse in agriculture. The sludge samples were collected from the water plant (WTP), wastewater treatment plant (WWTP), and industrial water treatment plant (IPT) in Taiwan. The inductively coupled plasma mass spectrometry was used to measure the trace metals in sludge. The pollution level and ecological risk criteria for heavy metals in sludge were also used to evaluate its reuse in agriculture. The result shows the average concentrations of trace metals in sludge for three groups (WTP, WWTP, and ITP). Significant correlations were found between concentrations of Zn-Ag (p < 0.001). The higher values of Igeo showed in ITP, indicated Hg to be a major pollutant. In Taiwan, the regulations did not establish the reuse of sludge in agriculture. However, the concentration level of trace metals in sludge was particularly lower than the regular levels in most groups, like WTP and WWTP groups. The industrial sludge was not recommended for the use in agriculture. The results of this study can be used for regular monitoring to establish a reference for sludge management and application to agriculture.

Genomic regions and pathways associated with thermotolerance in layer-type strain Taiwan indigenous chickens.

This study aimed to investigate genetic markers and candidate genes associated with thermotolerance in a layer-type strain Taiwan indigenous chickens exposed to acute heat stress. One hundred and ninety-two 30-week-old roosters were subjected to acute heat stress. Changes in body temperature (BT, ΔT) were calculated by measuring the difference between the initial BT and the highest BT during heat stress and the results were categorized into dead, susceptible, tolerant, and intermediate groups depending on their survival and ΔT values at the end of the experiment. A genome-wide association study on survival and ΔT values was conducted using the Cochran-Armitage trend test and Fisher's exact test. Association analyses identified 80 significant SNPs being annotated to 23 candidate genes, 440 SNPs to 71 candidate genes, 64 SNPs to 25 candidate genes, and 378 SNPs to 78 candidate genes in the dead versus survivor, tolerant versus susceptible, intermediate versus tolerant, and intermediate versus susceptible groups, respectively. The annotated genes were associated with apoptosis, cellular stress responses, DNA repair, and metabolic oxidative stress. In conclusion, the identified SNPs of candidate genes provide insights into the potential mechanisms underlying physiological responses to acute heat stress in chickens.

Dry and wet seasonal variation of total mercury, inorganic mercury, and methylmercury formation in estuary and harbor sediments.

This study analyzed the seasonal variations and the spatial distributions of total mercury (THg), inorganic divalent mercury (IHg), and methylmercury (MeHg) in sediments of river mouth (RM), main channel (MC), and entrance (E) of the Port of Kaohsiung, Taiwan. The THg, IHg, and MeHg concentrations were, respectively, 198-9130, 2.6-3164, and <0.3-42.6 µg/kg in the wet season and 362-2264, 11.0-790, and 3.3-65.6 µg/kg in the dry season. As for seasonal variations, the concentrations of THg and IHg for RM sediment were higher in the wet season than in the dry season, whereas for MC and E was converse. Generally, MeHg in sediment was higher in the dry season than in the wet season. THg and IHg were mainly transported from the river, whereas MeHg was generated by onsite microbes transforming the local available IHg. Results indicated that the formation of MeHg in sediment may be mainly influenced by the concentration of IHg and seasonal variations.

Detecting phthalate esters in sludge particulates from wastewater treatment plants.

This study proposed a method for analysis of 10 phthalate esters compounds from wastewater treatment plant sludges. The analytical efficiency of GC-MS for of target compounds was verified by a standard mixture of phthalate esters. The response factors related to the respective internal standards from a five-point calibration curve quantified the phthalate esters in individual compounds. Based on the literature compiled by environmental agencies, new generation phthalate compounds have been developed, such as di-iso-nonyl phthalate (DiNP), di-iso-decyl phthalate (DiDP), as alternative to conventional phthalates. The analytical results showed that the total PAEs concentration was in the range from 7.4 to 138.6 mg kg-1 dw in these seven analyzed sludge samples. More, di-iso-nonyl phthalate (DiNP), di-iso-decyl phthalate (DiDP) and bis(2-ethylhexyl) phthalate (DEHP) contributed to over 99% of PAEs in the sludge. The correlation between total PAEs concentration in household and sewage flow treated at seven WWTPs and concentrations of DEHP, DiNP and DiDP was significant.

Morpho-regulation in diverse chicken feather formation: Integrating branching modules and sex hormone-dependent morpho-regulatory modules.

Many animals can change the size, shape, texture and color of their regenerated coats in response to different ages, sexes, or seasonal environmental changes. Here, we propose that the feather core branching morphogenesis module can be regulated by sex hormones or other environmental factors to change feather forms, textures or colors, thus generating a large spectrum of complexity for adaptation. We use sexual dimorphisms of the chicken to explore the role of hormones. A long-standing question is whether the sex-dependent feather morphologies are autonomously controlled by the male or female cell types, or extrinsically controlled and reversible. We have recently identified core feather branching molecular modules which control the anterior-posterior (bone morphogenetic orotein [BMP], Wnt gradient), medio-lateral (Retinoic signaling, Gremlin), and proximo-distal (Sprouty, BMP) patterning of feathers. We hypothesize that morpho-regulation, through quantitative modulation of existing parameters, can act on core branching modules to topologically tune the dimension of each parameter during morphogenesis and regeneration. Here, we explore the involvement of hormones in generating sexual dimorphisms using exogenously delivered hormones. Our strategy is to mimic male androgen levels by applying exogenous dihydrotestosterone and aromatase inhibitors to adult females and to mimic female estradiol levels by injecting exogenous estradiol to adult males. We also examine differentially expressed genes in the feathers of wildtype male and female chickens to identify potential downstream modifiers of feather morphogenesis. The data show male and female feather morphology and their color patterns can be modified extrinsically through molting and resetting the stem cell niche during regeneration.

Acute Heat Stress Changes Protein Expression in the Testes of a Broiler-Type Strain of Taiwan Country Chickens.

Heat stress leads to decreased fertility in roosters. This study investigated the global protein expression in response to acute heat stress in the testes of a broiler-type strain of Taiwan country chickens (TCCs). Twelve 45-week-old roosters were randomly allocated to the control group maintained at 25°C, and three groups subjected to acute heat stress at 38°C for 4 h, with 0, 2, and 6 h of recovery, respectively. Testis samples were collected for hematoxylin and eosin staining, apoptosis assay, and protein analysis. The results revealed 101 protein spots that differed significantly from the control following exposure to acute heat stress. The proteins that were differentially expressed participated mainly in protein metabolism and other metabolic processes, responses to stimuli, apoptosis, cellular organization, and spermatogenesis. Proteins that negatively regulate apoptosis were downregulated and proteins involved in autophagy and major heat shock proteins (HSP90α, HSPA5, and HSPA8) were upregulated in the testes of heat-stressed chickens. In conclusion, acute heat stress causes a change in protein expression in the testes of broiler-type B strain TCCs and may thus impair cell morphology, spermatogenesis, and apoptosis. The expression of heat shock proteins increased to attenuate the testicular injury induced by acute heat stress.

Genome-wide association study on the body temperature changes of a broiler-type strain Taiwan country chickens under acute heat stress.

Body temperature is the simplest parameter for evaluating the physiological conditions of animals under thermal stress. Genome-wide association studies (GWAS) have identified candidate genes related to economic traits in domestic animals. The present study conducted a GWAS on body temperature changes in a broiler-type strain Taiwan country chickens (TCCs) under acute heat stress. A total of two hundred 30-week-old roosters of a broiler-type strain TCCs were used. The roosters were subjected to acute heat stress at 38 °C for 4 h, and their body temperature was recorded before and during heat stress. The change in body temperature (ΔT) of each rooster was calculated according to the difference between the initial temperature and the highest body temperature during heat stress. The roosters were categorized according to survival and ΔT at the end into dead, susceptible, resistant, and intermediate groups. Collected red blood cells were genotyped using a 600 K chicken single-nucleotide polymorphism (SNP) array. A GWAS for ΔT was conducted using the Cochran-Armitage trend test. Significant SNPs were annotated as candidate genes according to the nearest genes. Results indicated that the ΔT of the heat-resistant group was significantly lower than that of the heat-susceptible group. A total of 17 SNPs belonging to 8 candidate genes, 352 SNPs for 78 candidate genes, and 174 significant SNPs for 63 candidate genes were identified in the association analyses in the dead vs. survival, resistant vs. susceptible, and intermediate vs. susceptible groups, respectively. The annotated candidate genes are associated with apoptosis, cellular response to external stimuli, and signal transduction pathways. In conclusion, the significant SNPs located in and proximal to genes in the GWAS analysis were related to apoptosis or responses to external stimuli which serve as potential candidates underlying physiological adaptation to heat stress or thermotolerance in chickens.

Semi-quantification of the minimum detectable difference of imaging quality of gamma camera SPET for four radionuclides via an innovative PMMA phantom with a V-shaped slit: interpretation of a feasibility study.

OBJECTIVE: An indigenous polymethyl metacrylate (PMMA) phantom with a V-shaped slit and a correlated technique for semi-quantifying the minimum detectable difference (MDD) of single photon emission tomography (SPET) via gamma camera scanning are proposed and validated using four radionuclides. MATERIALS AND METHODS: Radio-actinide solutions of gallium-67 (67Ga), technetium-99m (99mTc), iodine-131 (131I) and thallium-201 (201Tl) were diluted to 11c.c. and thoroughly injected into the continuous zig zag slit of the PMMA phantom. Either depth or edge of the slit between two lines of the V-shape was customized from deep or wide to change into shallow or narrow gradually. Thus, the quantified MDD could be easily evaluated, according to the revised Student's t-test evaluation. The revised Student's t-test was calculated by both full width at half maximum (FWHM) and edge width between two adjacent peaks that were acquired from the original data matrix of SPET. The derived MDD was indicated as for radionuclide, depth, width in mm: For 67Ga, 2.9, 2.13, for 99mTc, 2.5, 0.66, for 131I, 4.7, 2.38 and for 201Tl, 3.3, 2.00, respectively. RESULTS: Technetium-99m had the highest and 131I had the lowest MDD among the four radionuclides. Furthermore, two adjacent peaks of 67Ga could be easily identified with fewer counts than for 201Tl (depth, 2.9 vs. 3.3mm), but its MDD was poorer (width: 2.13 vs.2.00mm). The revised Student's t-test analysis proved to be an acceptable technique for the MDD identification. CONCLUSION: The proposed new combination of PMMA phantom with a V-slit and the revised Student's t-test proved to be instrumental in the MDD of SPET optimization analysis.

Annotation of differential protein expression in the hypothalami of layer-type Taiwan country chickens in response to acute heat stress.

The hypothalamus is the coordinating center for maintaining temperature homeostasis. In this study, global protein expression in the hypothalami of layer-type Taiwan country chickens in response to acute heat stress was investigated. Twelve 30-week-old female TCCs were divided into three acute heat-stressed groups, namely acute heat stress at 36 °C for 4 h with 0 h (without recovery, H4R0), 2 h (H4R2), or 6 h (H4R6) of recovery. A control group was maintained at 25 °C. Hypothalamus samples were collected at the end of each time point for proteomic analysis. The analysis results revealed that 134 protein spots representing 118 distinct proteins exhibited differential expressions after acute heat stress treatment. Results of gene ontology analysis showed that most of the differentially expressed proteins are involved in carbohydrate metabolism, cellular processes, actin cytoskeleton organization, and responses to stimuli. Functional pathway analysis results suggested that the proteins are associated with networks of carbon metabolism, glycolysis, and gluconeogenesis. Upregulation of the expression of triosephosphate isomerase, phosphoglycerate kinase, pyruvate kinase, alpha-enolase, glycogen phosphorylase (brain form), phosphoglucomutase, L-lactate dehydrogenase A chain and downregulation of 6-phosphogluconolactonase expression indicated an increase in the glycolytic activity and glucose supply for ATP production in the hypothalami in response to heat stress. By contrast, upregulated expressions of heat shock protein 90 alpha, glutathione S-transferase 2s, peroxiredoxin-1, and dihydropyrimidinase-like 2 suggested that acute heat stress adversely affects the hypothalamus; thus, it induces mechanisms that prevent oxidative damage and endoplasmic reticulum stress. In conclusion, acute heat stress induces differential protein expression in the hypothalami of the L2 strain Taiwan country chickens, which may manifest detrimental effects. Furthermore, differential expression is a critical response in the hypothalamus for the regulation of thermotolerance.

Effect of seasonal changes on fertility parameters of Holstein dairy cows in subtropical climate of Taiwan.

OBJECTIVE: The purpose of this retrospective study was to investigate the relationship between temperature-humidity index (THI), season, and conception rate (CR) of Holstein cows in central Taiwan. METHODS: The mean performance and number of observations were statistically evaluated for various parameters, including age at first service, number of days open, gestation length, CR, and calving interval for different parities. RESULTS: The results indicate that the mean age at first service was 493.2 days; the gestation length was similar across all cows of different parities, ranging from 275.1 to 280.7 days. The overall CR of all inseminations was significantly lower in multiparous cows (47.26%±0.22%) than in heifers (57.14%±0.11%) (p<0.05). At THI>72 and during the hot season (from June to November), CRs for multiparous cows were significantly reduced compared to that for heifers, while the ratio remained unchanged among heifers for all seasons. CONCLUSION: To achieve a high CR, lactating cows should be bred in winter and spring (from December to May) from the start of the seasonal breeding program, whereas the heifer should be allowed to breed in summer and fall under the subtropical climate in Taiwan.

Detection of QTL for traits related to adaptation to sub-optimal climatic conditions in chickens.

BACKGROUND: Growth traits can be used as indicators of adaptation to sub-optimal conditions. The current study aimed at identifying quantitative trait loci (QTL) that control performance under variable temperature conditions in chickens. METHODS: An F2 population was produced by crossing the Taiwan Country chicken L2 line (selected for body weight, comb area, and egg production) with an experimental line of Rhode Island Red layer R- (selected for low residual feed consumption). A total of 844 animals were genotyped with the 60 K Illumina single nucleotide polymorphism (SNP) chip. Whole-genome interval linkage mapping and a genome-wide association study (GWAS) were performed for body weight at 0, 4, 8, 12, and 16 weeks of age, shank length at 8 weeks of age, size of comb area at 16 weeks of age, and antibody response to sheep red blood cells at 11 weeks of age (7 and 14 days after primary immunization). Relevant genes were identified based on functional annotation of candidate genes and potentially relevant SNPs were detected by comparing whole-genome sequences of several birds between the parental lines. RESULTS: Whole-genome QTL analysis revealed 47 QTL and 714 effects associated with 178 SNPs were identified by GWAS with 5% Bonferroni genome-wide significance. Little overlap was observed between the QTL and GWAS results, with only two chromosomal regions detected by both approaches, i.e. one on GGA24 (GGA for Gallus gallus chromosome) for BW04 and one on GGAZ for six growth-related traits. Based on whole-genome sequence, differences between the parental lines based on several birds were screened in the genome-wide QTL regions and in a region detected by both methods, resulting in the identification of 106 putative candidate genes with a total of 15,443 SNPs, of which 41 were missense and 1698 were not described in the dbSNP archive. CONCLUSIONS: The QTL detected in this study for growth and morphological traits likely influence adaptation of chickens to sub-tropical climate. Using whole-genome sequence data, we identified candidate SNPs for further confirmation of QTL in the F2 design. A strong QTL effect found on GGAZ underlines the importance of sex-linked inheritance for growth traits in chickens.

Characterization of the testicular regeneration potential in premature cockerels.

Previous studies have shown that grafted neonatal chicken testicular tissue can develop and produce functional sperm; however, it was unclear whether regenerative processes or proportional growth caused the re-appearance of spermatogenic tissue. We dissociated testicular tissues, performed subcutaneous auto-transplantation of the re-aggregated cells to castrated cockerels, and monitored the post-surgery development of these transplanted aggregates. We found that these transplanted cell aggregates experienced compensatory growth in the form of a 300-fold increase in size, rather than the 30-fold increase observed in normal testis development. Further, these dissociated testicular cell aggregates restored seminiferous tubule structure and were able to produce testosterone and motile sperm. Therefore, we concluded that the dissociated testicular cells from 11-week-old cockerels retained a strong regenerative potential, as they exhibited compensatory growth, restored destroyed structure, and sustained spermatogenesis.

Transcriptomic analyses of regenerating adult feathers in chicken.

BACKGROUND: Feathers have diverse forms with hierarchical branching patterns and are an excellent model for studying the development and evolution of morphological traits. The complex structure of feathers allows for various types of morphological changes to occur. The genetic basis of the structural differences between different parts of a feather and between different types of feather is a fundamental question in the study of feather diversity, yet there is only limited relevant information for gene expression during feather development. RESULTS: We conducted transcriptomic analysis of five zones of feather morphologies from two feather types at different times during their regeneration after plucking. The expression profiles of genes associated with the development of feather structure were examined. We compared the gene expression patterns in different types of feathers and different portions of a feather and identified morphotype-specific gene expression patterns. Many candidate genes were identified for growth control, morphogenesis, or the differentiation of specific structures of different feather types. CONCLUSION: This study laid the ground work for studying the evolutionary origin and diversification of feathers as abundant data were produced for the study of feather morphogenesis. It significantly increased our understanding of the complex molecular and cellular events in feather development processes and provided a foundation for future studies on the development of other skin appendages.

The chicken frizzle feather is due to an α-keratin (KRT75) mutation that causes a defective rachis.

Feathers have complex forms and are an excellent model to study the development and evolution of morphologies. Existing chicken feather mutants are especially useful for identifying genetic determinants of feather formation. This study focused on the gene F, underlying the frizzle feather trait that has a characteristic curled feather rachis and barbs in domestic chickens. Our developmental biology studies identified defects in feather medulla formation, and physical studies revealed that the frizzle feather curls in a stepwise manner. The frizzle gene is transmitted in an autosomal incomplete dominant mode. A whole-genome linkage scan of five pedigrees with 2678 SNPs revealed association of the frizzle locus with a keratin gene-enriched region within the linkage group E22C19W28_E50C23. Sequence analyses of the keratin gene cluster identified a 69 bp in-frame deletion in a conserved region of KRT75, an α-keratin gene. Retroviral-mediated expression of the mutated F cDNA in the wild-type rectrix qualitatively changed the bending of the rachis with some features of frizzle feathers including irregular kinks, severe bending near their distal ends, and substantially higher variations among samples in comparison to normal feathers. These results confirmed KRT75 as the F gene. This study demonstrates the potential of our approach for identifying genetic determinants of feather forms.