Genetics and Genomics Commons^™

Genomic Insights Into The Mystery Of Mouse Mummies On The Summits Of Atacama Volcanoes, Jay F. Storz, Schuyler Liphardt, Marcial Quiroga-Carmona, Naim M. Bautista, Juan C. Opazo, Guillermo D’Elía, Jeffrey M. Good

Jay F. Storz Publications

Our understanding of the limits of animal life is continually revised by scientific exploration of extreme environments. Here we report the discovery of mummified cadavers of leaf-eared mice, Phyllotis vaccarum, from the summits of three different Andean volcanoes at elevations 6,029–6,233 m above sea level in the Puna de Atacama in Chile and Argentina. Such extreme elevations were previously assumed to be completely uninhabitable by mammals. In combination with a live-captured specimen of the same species from the nearby summit of Volcán Llullaillaco (6,739 m),¹ the summit mummies represent the highest altitude physical records of mammals in the …

Predictable Convergence In Hemoglobin Function Has Unpredictable Molecular Underpinnings, Chandrasekhar Natarajan, Federico G. Hoffmann, Roy E. Weber, Angela Fago, Christopher C. Witt, Jay F. Storz

Jay F. Storz Publications

To investigate the predictability of genetic adaptation, we examined the molecular basis of convergence in hemoglobin function in comparisons involving 56 avian taxa that have contrasting altitudinal range limits. Convergent increases in hemoglobin-oxygen affinity were pervasive among high-altitude taxa, but few such changes were attributable to parallel amino acid substitutions at key residues.Thus, predictable changes in biochemical phenotype do not have a predictable molecular basis. Experiments involving resurrected ancestral proteins revealed that historical substitutions have context-dependent effects, indicating that possible adaptive solutions are contingent on prior history. Mutations that produce an adaptive change in one species may represent precluded possibilities …

Oxygenation Properties And Isoform Diversity Of Snake Hemoglobins, Jay F. Storz, Chandrasekhar Natarajan, Hideaki Moriyama, Federico G. Hoffmann, Tobias Wang, Angela Fago, Hans Malte, Johannes Overgaard, Roy E. Weber

Jay F. Storz Publications

Available data suggest that snake hemoglobins (Hbs) are characterized by a combination of unusual structural and functional properties relative to the Hbs of other amniote vertebrates, including oxygenation-linked tetramer-dimer dissociation. However, standardized comparative data are lacking for snake Hbs, and the Hb isoform composition of snake red blood cells has not been systematically characterized. Here we present the results of an integrated analysis of snake Hbs and the underlying α- and β-type globin genes to characterize 1) Hb isoform composition of definitive erythrocytes, and 2) the oxygenation properties of isolated isoforms as well as composite hemolysates. We used species from …

Comparative Genomics Reveals Insights Into Avian Genome Evolution And Adaptation, Guojie Zhang, Cai Li, Qiye Li, Bo Li, Dennis M. Larkin, Chul Lee, Jay F. Storz, Agostinho Antunes, Matthew J. Greenwold, Robert W. Meredith, Anders Ödeen, Jie Cui, Qi Zhou, Luohao Xu, Hailin Pan, Zongji Wang, Lijun Jin, Pei Zhang, Haofu Hu, Wei Yang, Jiang Hu, Jin Xiao, Zhikai Yang, Yang Liu, Qiaolin Xie, Hao Yu, Jinmin Lian, Ping Wen, Fang Zhang, Hui Li, Yongli Zeng, Zijun Xiong, Shiping Liu, Long Zhou, Zhiyong Huang, Na An, Jie Wang, Quimei Zheng, Yingqi Xiong, Guangbiao Wang, Bo Wang, Jingjing Wang, Yu Fan, Rute R. Da Fonseca, Alonzo Alfaro-Núñez, Mikkel Schubert, Ludovic Orlando, Tobias Mourier, Jason T. Howard, Ganeshkumar Ganapathy, Andreas Pfenning, Osceola Whitney, Miriam V. Rivas, Erina Hara, Julia Smith, Marta Farré, Jitendra Narayan, Gancho Slavov, Michael N. Romanov, Rui Borges, João Paulo Machado, Imran Khan, Mark S. Springer, John Gatesy, Federico G. Hoffmann, Juan C. Opazo, Olle Håstad, Roger H. Sawyer, Heebal Kim, Kyu-Won Kim, Hyeon Jeong Kim, Seoae Cho, Ning Li, Yinhua Huang, Michael W. Bruford, Xiangjiang Zhan, Andrew Dixon, Mads F. Bertelsen, Elizabeth Derryberry, Wesley Warren, Richard K. Wilson, Shengbin Li, David A. Ray, Richard E. Green, Stephen J. O'Brien, Darren Griffin, Warren E. Johnson, David Haussler, Oliver A. Ryder, Eske Willerslev, Gary R. Graves, Per Alström, Jon Fjeldså, David P. Mindell, Scott V. Edwards, Edward L. Braun, Carsten Rahbek, David W. Burt, Peter Houde, Yong Zhang, Huanming Yang, Jian Wang, Avian Genome Consortium, Erich D. Jarvis, M. Thomas P. Gilbert, Jun Wang

Jay F. Storz Publications

Birds are the most species-rich class of tetrapod vertebrates and have wide relevance across many research fields. We explored bird macroevolution using full genomes from 48 avian species representing all major extant clades. The avian genome is principally characterized by its constrained size, which predominantly arose because of lineage-specific erosion of repetitive elements, large segmental deletions, and gene loss. Avian genomes furthermore show a remarkably high degree of evolutionary stasis at the levels of nucleotide sequence, gene synteny, and chromosomal structure. Despite this pattern of conservation, we detected many non-neutral evolutionary changes in protein-coding genes and noncoding regions. These analyses …

Oxygenation Properties And Oxidation Rates Of Mouse Hemoglobins That Differ In Reactive Cysteine Content, Jay F. Storz, Roy E. Weber, Angela Fago

Jay F. Storz Publications

House mice (genus Mus) harbor extensive allelic variation at two tandemly duplicated genes that encode the β-chain subunits of adult hemoglobin (Hb). Alternative haplotypes differ in the level of sequence divergence between the two β-globin gene duplicates: the Hbb^d and Hbb^p haplotypes harbor two structurally distinct β-globin genes, whereas the Hbb^s haplotype harbors two β-globin duplicates that are identical in sequence. One especially salient difference between the s-type Hbs relative to the d- and p-type Hbs relates to the number of reactive β-chain cysteine residues. In addition to the highly conserved cysteine residue …

Regulatory Changes Contribute To The Adaptive Enhancement Of Thermogenic Capacity In High-Altitude Deer Mice, Zachary A. Cheviron, Gwendolyn C. Bachman, Alex D. Connaty, Jay F. Storz

Jay F. Storz Publications

In response to hypoxic stress, many animals compensate for a reduced cellular O₂ supply by suppressing total metabolism, thereby reducing O₂ demand. For small endotherms that are native to high-altitude environments, this is not always a viable strategy, as the capacity for sustained aerobic thermogenesis is critical for survival during periods of prolonged cold stress. For example, survivorship studies of deer mice (Peromyscus maniculatus) have demonstrated that thermogenic capacity is under strong directional selection at high altitude. Here, we integrate measures of whole-organism thermogenic performance with measures of metabolic enzyme activities and genomic transcriptional profiles to …

Phylogenetic Diversification Of The Globin Gene Superfamily In Chordates, Jay F. Storz, Juan C. Opazo, Federico G. Hoffmann

Jay F. Storz Publications

Phylogenetic reconstructions provide a means of inferring the branching relationships among members of multigene families that have diversified via successive rounds of gene duplication and divergence. Such reconstructions can illuminate the pathways by which particular expression patterns and protein functions evolved. For example, phylogenetic analyses can reveal cases in which similar expression patterns or functional properties evolved independently in different lineages, either through convergence, parallelism, or evolutionary reversals. The purpose of this article is to provide a robust phylogenetic framework for interpreting experimental data and for generating hypotheses about the functional evolution of globin proteins in chordate animals. To do …

Expression And Purification Of Recombinant Hemoglobin In Escherichia Coli, Chandrasekhar Natarajan, Xiaoben Jiang, Angela Fago, Roy E. Weber, Hideaki Moriyama, Jay F. Storz

Jay F. Storz Publications

Background: Recombinant DNA technologies have played a pivotal role in the elucidation of structure-function relationships in hemoglobin (Hb) and other globin proteins. Here we describe the development of a plasmid expression system to synthesize recombinant Hbs in Escherichia coli, and we describe a protocol for expressing Hbs with low intrinsic solubilities. Since the alpha- and beta-chain Hbs of different species span a broad range of solubilities, experimental protocols that have been optimized for expressing recombinant human HbA may often prove unsuitable for the recombinant expression of wildtype and mutant Hbs of other species.

Methodology/Principal Findings: As a test case …

Developmental Regulation Of Hemoglobin Synthesis In The Green Anole Lizard Anolis Carolinensis, Jay F. Storz, Federico G. Hoffmann, Juan C. Opazo, Thomas J. Sanger, Hideaki Moriyama

Jay F. Storz Publications

Tetrapod vertebrates possess multiple alpha- and beta-like globin genes that are ontogenetically regulated, such that functionally distinct hemoglobin (Hb) isoforms are synthesized during different stages of development. The alpha- and beta-like globin genes of amphibians, birds and mammals are differentially expressed during embryonic development and postnatal life, but little is known about the developmental regulation of globin gene expression in non-avian reptiles. Here we report an investigation into the developmental regulation of Hb synthesis in the green anole lizard Anolis carolinensis. We tested two hypotheses derived from comparative genomic studies of the globin gene clusters in tetrapod vertebrates. First, …

Evolutionary Origins Of Oxygen Sensing In Animals, Kalle T. Rytkönen, Jay F. Storz

Jay F. Storz Publications

All animal life requires molecular oxygen as the terminal electron acceptor in aerobic energy production. A lack of oxygen can reduce the rate of energy production, whereas an excess of oxygen leads to the accumulation of toxic reactive oxygen species. Hence, animals have evolved sophisticated mechanisms with which to monitor and respond to fluctuations in oxygen availability, in order to maintain cellular homeostasis. In all animal taxa examined so far, the maintenance of physiological oxygen homeostasis is mediated by the oxygen-dependent post-translational hydroxylation of a heterodimeric transcription factor, termed hypoxia-inducible factor (HIF; Kaelin & Ratcliffe, 2008). The hydroxylation reaction is …

Differential Loss And Retention Of Cytoglobin, Myoglobin, And Globin-E During The Radiation Of Vertebrates, Federico G. Hoffmann, Juan C. Opazo, Jay F. Storz

Jay F. Storz Publications

If rates of postduplication gene retention are positively correlated with levels of functional constraint, then gene duplicates that have been retained in a restricted number of taxonomic lineages would be expected to exhibit relatively low levels of sequence conservation. Paradoxical patterns are presented by gene duplicates that have been retained in a small number of taxa but which are nonetheless subject to strong purifying selection relative to paralogous members of the same multigene family. This pattern suggests that such genes may have been co-opted for novel, lineage-specific functions. One possible example involves the enigmatic globin-E gene (GbE), which …

Experimental Approaches To Evaluate The Contributions Of Candidate Protein-Coding Mutations To Phenotypic Evolution, Jay F. Storz, Anthony J. Zera

Jay F. Storz Publications

Identifying mechanisms of molecular adaptation can provide important insights into the process of phenotypic evolution, but it can be exceedingly difficult to quantify the phenotypic effects of specific mutational changes. To verify the adaptive significance of genetically based changes in protein function, it is necessary to document functional differences between the products of derived and wild-type alleles and to demonstrate that such differences impinge on higher-level physiological processes (and ultimately, fitness). In the case of metabolic enzymes, this requires documenting in vivo differences in reaction rate that give rise to differences in flux through the pathway in which the enzymes …

Structure And Reactivity Of Hexacoordinate Hemoglobins, Smita Kakar, Federico G. Hoffmann, Jay F. Storz, Marian Fabian, Mark S. Hargrove

Jay F. Storz Publications

The heme prosthetic group in hemoglobins is most often attached to the globin through coordination of either one or two histidine side chains. Those proteins with one histidine coordinating the heme iron are called “pentacoordinate” hemoglobins, a group represented by red blood cell hemoglobin and most other oxygen transporters. Those with two histidines are called “hexacoordinate hemoglobins”, which have broad representation among eukaryotes. Coordination of the second histidine in hexacoordinate Hbs is reversible, allowing for binding of exogenous ligands like oxygen, carbon monoxide, and nitric oxide. Research over the past several years has produced a fairly detailed picture of the …

Integrating Evolutionary And Functional Approaches To Infer Adaptation At Specific Loci, Jay F. Storz, Christopher W. Wheat

Jay F. Storz Publications

Inferences about adaptation at specific loci are often exclusively based on the static analysis of DNA sequence variation. Ideally, population-genetic evidence for positive selection serves as a stepping-off point for experimental studies to elucidate the functional significance of the putatively adaptive variation. We argue that inferences about adaptation at specific loci are best achieved by integrating the indirect, retrospective insights provided by population-genetic analyses with the more direct, mechanistic insights provided by functional experiments. Integrative studies of adaptive genetic variation may sometimes be motivated by experimental insights into molecular function, which then provide the impetus to perform population genetic tests …

Gene Cooption And Convergent Evolution Of Oxygen Transport Hemoglobins In Jawed And Jawless Vertebrates, Federico G. Hoffmann, Juan C. Opazo, Jay F. Storz

Jay F. Storz Publications

Natural selection often promotes evolutionary innovation by coopting preexisting genes for new functions, and this process may be greatly facilitated by gene duplication. Here we report an example of cooptive convergence where paralogous members of the globin gene superfamily independently evolved a specialized O₂ transport function in the two deepest branches of the vertebrate family tree. Specifically, phylogenetic evidence demonstrates that erythroidspecific O₂ transport hemoglobins evolved independently from different ancestral precursor proteins in jawed vertebrates (gnathostomes) and jawless fish (cyclostomes, represented by lamprey and hagfish). A comprehensive phylogenetic analysis of the vertebrate globin gene superfamily revealed that the …

Genes For High Altitudes, Jay F. Storz

Jay F. Storz Publications

Analyses of genomes from Tibetan populations reveal a signaling pathway that may account for high-altitude adaptation. Tibetans, who have lived at high altitudes for nearly 25,000 years, survive the low-oxygen environment through a low blood hemoglobin concentration.

Lineage-Specific Patterns Of Functional Diversification In The Α- And Β-Globin Gene Families Of Tetrapod Vertebrates, Federico G. Hoffmann, Jay F. Storz, Thomas A. Gorr, Juan C. Opazo

Jay F. Storz Publications

The α- and β-globin gene families of jawed vertebrates have diversified with respect to both gene function and the developmental timing of gene expression. Phylogenetic reconstructions of globin gene family evolution have provided suggestive evidence that the developmental regulation of hemoglobin synthesis has evolved independently in multiple vertebrate lineages. For example, the embryonic β-like globin genes of birds and placental mammals are not 1:1 orthologs. Despite the similarity in developmental expression profiles, the genes are independently derived from lineage-specific duplications of a β-globin pro-ortholog. This suggests the possibility that other vertebrate taxa may also possess distinct repertoires of globin genes …

Genetic Differences In Hemoglobin Function Between Highland And Lowland Deer Mice, Jay F. Storz, Amy M. Runck, Hideaki Moriyama, Roy E. Weber, Angela Fago

Jay F. Storz Publications

In high-altitude vertebrates, adaptive changes in blood–O₂ affinity may be mediated by modifications of hemoglobin (Hb) structure that affect intrinsic O₂ affinity and/or responsiveness to allosteric effectors that modulate Hb–O₂ affinity. This mode of genotypic specialization is considered typical of mammalian species that are high-altitude natives. Here we investigated genetically based differences in Hb–O₂ affinity between highland and lowland populations of the deer mouse (Peromyscus maniculatus), a generalist species that has the broadest altitudinal distribution of any North American mammal. The results of a combined genetic and proteomic analysis revealed that deer mice harbor …

Phenotypic Plasticity And Genetic Adaptation To High-Altitude Hypoxia In Vertebrates, Jay F. Storz, Graham R. Scott, Zachary A. Cheviron

Jay F. Storz Publications

High-altitude environments provide ideal testing grounds for investigations of mechanism and process in physiological adaptation. In vertebrates, much of our understanding of the acclimatization response to high-altitude hypoxia derives from studies of animal species that are native to lowland environments. Such studies can indicate whether phenotypic plasticity will generally facilitate or impede adaptation to high altitude. Here, we review general mechanisms of physiological acclimatization and genetic adaptation to high-altitude hypoxia in birds and mammals. We evaluate whether the acclimatization response to environmental hypoxia can be regarded generally as a mechanism of adaptive phenotypic plasticity, or whether it might sometimes represent …

Molecular Basis Of A Novel Adaptation To Hypoxic-Hypercapnia In A Strictly Fossorial Mole, Kevin L. Campbell, Jay F. Storz, Anthony V. Signore, Hideaki Moriyama, Kenneth C. Catania, Alexander P. Payson, Joseph Bonaventura, Jörg Stetefeld, Roy E. Weber

Jay F. Storz Publications

Background: Elevated blood O₂ affinity enhances survival at low O₂ pressures, and is perhaps the best known and most broadly accepted evolutionary adjustment of terrestrial vertebrates to environmental hypoxia. This phenotype arises by increasing the intrinsic O₂ affinity of the hemoglobin (Hb) molecule, by decreasing the intracellular concentration of allosteric effectors (e.g., 2,3-diphosphoglycerate; DPG), or by suppressing the sensitivity of Hb to these physiological cofactors.

Results: Here we report that strictly fossorial eastern moles (Scalopus aquaticus) have evolved a low O₂ affinity, DPG-insensitive Hb - contrary to expectations for a mammalian species that is …

Evolutionary And Functional Insights Into The Mechanism Underlying High-Altitude Adaptation Of Deer Mouse Hemoglobin, Jay F. Storz, Amy M. Runck, Stephen J. Sabatino, John K. Kelly, Nuno Ferrand, Hideaki Moriyama, Roy E. Weber, Angela Fago

Jay F. Storz Publications

Adaptive modifications of heteromeric proteins may involve genetically based changes in single subunit polypeptides or parallel changes in multiple genes that encode distinct, interacting subunits. Here we investigate these possibilities by conducting a combined evolutionary and functional analysis of duplicated globin genes in natural populations of deer mice (Peromyscus maniculatus) that are adapted to different elevational zones. A multilocus analysis of nucleotide polymorphism and linkage disequilibrium revealed that high-altitude adaptation of deer mouse hemoglobin involves parallel functional differentiation at multiple unlinked gene duplicates: two α-globin paralogs on chromosome 8 and two β-globin paralogs on chromosome 1. Differences in …

Molecular Evolution Of Cytochrome B In High- And Low-Altitude Deer Mice (Genus Peromyscus), E. J. Gering, J. C. Opazo, Jay F. Storz

Jay F. Storz Publications

Patterns of amino-acid polymorphism in human mitochondrial genes have been interpreted as evidence for divergent selection among populations that inhabit climatically distinct environments. If similar patterns are mirrored in other broadly distributed mammalian species, then adaptive modifications of mitochondrial protein function may be detected in comparisons among locally adapted populations of a single wide-ranging species, or among closely related species that have adapted to different environments. Here, we test for evidence of positive selection on cytochrome b variation within and among species of the ecologically diverse rodent genus Peromyscus. We used likelihood-based comparisons of synonymous and nonsynonymous substitution rates to …

Evolution Of Duplicated Β-Globin Genes And The Structural Basis Of Hemoglobin Isoform Differentiation In Mus, Amy M. Runck, Hideaki Moriyama, Jay F. Storz

Jay F. Storz Publications

The functional diversification of multigene families may be strongly influenced by mechanisms of concerted evolution such as interparalog gene conversion. The β-globin gene family of house mice (genus Mus) represents an especially promising system for evaluating the effects of gene conversion on the functional divergence of duplicated genes. Whereas the majority of mammalian species possess tandemly duplicated copies of the adult β-globin gene that are identical in sequence, natural populations of house mice are often polymorphic for distinct two-locus haplotypes that differ in levels of functional divergence between duplicated β-globin genes, HBB-T1 and HBB-T2. Here, we use a phylogenetic …

Gene Duplication And The Resolution Of Adaptive Conflict, Jay F. Storz

Jay F. Storz Publications

Gene duplication is known to play an important role in the evolution of novel protein functions. However, there is still much debate about the evolutionary mechanisms that are responsible for the initial retention and subsequent divergence of newly created gene duplicates (Lynch et al., 2001; Zhang, 2003; Lynch and Katju, 2004; Taylor and Raes, 2004). According to the neofunctionalization (NEOF) model of Ohno (1970), the functional redundancy of duplicated genes entails a relaxation of purifying selection that results in the accumulation of degenerative mutations in one gene copy, while the other duplicate copy continues to perform the essential tasks of …

Origin And Ascendancy Of A Chimeric Fusion Gene: The Β/Δ-Globin Gene Of Paenungulate Mammals, Juan C. Opazo, Angela M. Sloan, Kevin L. Campbell, Jay F. Storz

Jay F. Storz Publications

The δ-globin gene (HBD) of eutherian mammals exhibits a propensity for recombinational exchange with the closely linked β-globin gene (HBB) and has been independently converted by the HBB gene in multiple lineages. Here we report the presence of a chimeric β/δ fusion gene in the African elephant (Loxodonta africana) that was created by unequal crossing-over between misaligned HBD and HBB paralogs. The recombinant chromosome that harbors the β/δ fusion gene in elephants is structurally similar to the ‘‘anti-Lepore’’ duplication mutant of humans (the reciprocal exchange product of the hemoglobin Lepore deletion mutant). However, the situation in …

New Genes Originated Via Multiple Recombinational Pathways In The Β-Globin Gene Family Of Rodents, Frederico Hoffmann, Juan Opazo, Jay F. Storz

Jay F. Storz Publications

Species differences in the size or membership composition of multigene families can be attributed to lineage-specific additions of new genes via duplication, losses of genes via deletion or inactivation, and the creation of chimeric genes via domain shuffling or gene fusion. In principle, it should be possible to infer the recombinational pathways responsible for each of these different types of genomic change by conducting detailed comparative analyses of genomic sequence data. Here, we report an attempt to unravel the complex evolutionary history of the β-globin gene family in a taxonomically diverse set of rodent species. The main objectives were: 1) …

Differential Loss Of Embryonic Globin Genes During The Radiation Of Placental Mammals, Juan C. Opazo, Federico Hoffmann, Jay F. Storz

Jay F. Storz Publications

The differential gain and loss of genes from homologous gene families represents an important source of functional variation among the genomes of different species. Differences in gene content between species are primarily attributable to lineage-specific gene gains via duplication and lineage-specific losses via deletion or inactivation. Here, we use a comparative genomic approach to investigate this process of gene turnover in the β-globin gene family of placental mammals. By analyzing genomic sequence data from representatives of each of the main superordinal clades of placental mammals, we were able to reconstruct pathways of gene family evolution during the basal radiation of …

Evidence For Contrasting Modes Of Selection At Interacting Globin Genes In The European Rabbit (Oryctolagus Cuniculus), R. Campos, Jay F. Storz, N. Ferrand

Jay F. Storz Publications

In hybrid zones between genetically differentiated populations, variation in locus-specific rates of introgression may reflect adaptation to different environments or adaptation to different genetic backgrounds. The European rabbit, Oryctolagus cuniculus, is well-suited to studies of such hybrid zone dynamics because it is composed of two genetically divergent subspecies that hybridize in a zone of secondary contact in central Iberia. A species-wide survey of allozyme variation revealed a broad range of locus-specific divergence levels (F_ST ranged from 0 to 0.54, mean F_ST = 0.16). Interestingly, the two loci that fell at opposite ends of the distribution of …

Genomic Evidence For Independent Origins Of Β-Like Globin Genes In Monotremes And Therian Mammals, Juan C. Opazo, Federico G. Hoffmann, Jay F. Storz

Jay F. Storz Publications

Phylogenetic reconstructions of the β-globin gene family in vertebrates have revealed that developmentally regulated systems of hemoglobin synthesis have been reinvented multiple times in independent lineages. For example, the functional differentiation of embryonic and adult β-like globin genes occurred independently in birds and mammals. In both taxa, the embryonic β-globin gene is exclusively expressed in primitive erythroid cells derived from the yolk sac. However, the “ε-globin” gene in birds is not orthologous to the ε-globin gene in mammals, because they are independently derived from lineage-specific duplications of a proto β-globin gene. Here, we report evidence that the early and late …

Rapid Rates Of Lineage-Specific Gene Duplication And Deletion In The Α-Globin Gene Family, Federico G. Hoffmann, Juan C. Opazo, Jay F. Storz

Jay F. Storz Publications

Phylogeny reconstructions of the globin gene families have revealed that paralogous genes within species are often more similar to one another than they are to their orthologous counterparts in closely related species. This pattern has been previously attributed to mechanisms of concerted evolution such as interparalog gene conversion that homogenize sequence variation between tandemly duplicated genes and therefore create the appearance of recent common ancestry. Here we report a comparative genomic analysis of the α-globin gene family in mammals that reveal a surprisingly high rate of lineage-specific gene duplication and deletion via unequal crossing-over. Results of our analysis reveal that …