Prof Sir Walter Bodmer FRS
|Research Area:||Genetics and Genomics|
|Technology Exchange:||Biobanking, Bioinformatics, Cell sorting, Cellular immunology, Computational biology, Flow cytometry, Human genetics, Immunohistochemistry, Mass spectrometry, Medical statistics, Microscopy (Confocal), Microscopy (Video), Mouse models, Protein interaction, SNP typing, Statistical genetics and Transcript profiling|
|Scientific Themes:||Cancer and Genes, Genetics, Epigenetics & Genomics|
|Keywords:||colorectal cancer cell lines, cancer stem cells, differentiation, population genetics, transcriptional profiling and immunotherapy|
A single CD44+CD24+ cell from the SW1222 colorectal cell line can give rise to a large colony contai ...
Circulating tumour cells isolated by Lymphoprep (tm) from the peripheral blood of colorectal and pro ...
The major interests of this laboratory are in:
i)The fundamental genetics and biology of colorectal cancer (CRC) and their potential applications; and
ii)The characterisation and population distribution of genetic diversity in human populations, especially of the British Isles.
We have accumulated a panel of more than 100 colorectal carcinoma derived cell lines, representing more than 90 different independent tumours. The lines are extensively characterised with respect to genetic and epigenetic changes, as well as whole genome mRNA expression and other biological properties. The lines thus provide an invaluable resource for studying the basic biology of CRC, as well as CRC drug responses in relation to tumour properties.
We have, for example, been able to identify cancer stem cells in the lines and shown the importance of the homeobox gene, CDX1, for the control of columnar cell differentiation, as well as the role of hypoxia in blocking differentiation. We are now extending our studies to the identification of the major genes that control stemness and cellular differentiation in CRCs.
We have shown that the response of the cell lines to the direct effects of the anti EGFR monoclonal antibody, cetuximab, is strongly associated with being triple KRAS, BRAF, PIK3CA wild type and highly expressing epiregulin, closely paralleling clinical data. The immune mediated effects (largely ADCC), however, correlate with ERBB1 levels and not with the KRAS mutation status, effects that can only be seen with a sufficiently large number of lines. We are now working on characterising the responses of the cell lines to a wide variety of different drugs and antibodies and their combinations, with a view to identifying new effective treatment combinations and so helping to optimize the clinical treatment of CRCs.
Recently, we have had considerable success in growing out medium to long-term cultures from fresh CRC tumour material. These primary cultures are now being compared with the cell lines, both with respect to their biological properties and their drug responses.
We have a major interest in the study of genetic variability in human populations and have collected a control UK population that can be used for case-control and rare variant disease association studies, as well as providing the basis for characterising the genetic variation of the British population in relation to its history and origins. We have now accumulated more than 4000 DNA samples from people from throughout the UK in rural areas, all four of whose grandparents come from the same area. This approach aims to minimise the effects of more recent population admixture. A novel approach to the analysis of 500k snp data on a subset of over 2000 samples, in collaboration with colleagues in the statistics department, has shown remarkable geographic patterning of the genetic variability in the UK. We are also studying the genetics of normal differences, especially of facial features, in these population samples (see the website: http://www.peopleofthebritishisles.org/).
|Professor Peter Donnelly FRS||Wellcome Trust Centre for Human Genetics||University of Oxford||United Kingdom|
Nature, 519 (7543), pp. 309-14. Read abstract2015. The fine-scale genetic structure of the British population.
Fine-scale genetic variation between human populations is interesting as a signature of historical demographic events and because of its potential for confounding disease studies. We use haplotype-based statistical methods to analyse genome-wide single nucleotide polymorphism (SNP) data from a carefully chosen geographically diverse sample of 2,039 individuals from the United Kingdom. This reveals a rich and detailed pattern of genetic differentiation with remarkable concordance between genetic clusters and geography. The regional genetic differentiation and differing patterns of shared ancestry with 6,209 individuals from across Europe carry clear signals of historical demographic events. We estimate the genetic contribution to southeastern England from Anglo-Saxon migrations to be under half, and identify the regions not carrying genetic material from these migrations. We suggest significant pre-Roman but post-Mesolithic movement into southeastern England from continental Europe, and show that in non-Saxon parts of the United Kingdom, there exist genetically differentiated subgroups rather than a general 'Celtic' population. Hide abstract
J. Pathol., 234 (1), pp. 34-45. Read abstract2014. Rapidly derived colorectal cancer cultures recapitulate parental cancer characteristics and enable personalized therapeutic assays.
We have developed a simple procedure for deriving pure cultures of growing cancer cells from colorectal cancers, including material refrigerated overnight, for pathological characterization and cytotoxicity assays. Forty-six cancers were processed and cultures set up under varying culture conditions. Use of a Rho kinase (ROCK1) inhibitor markedly increased culture survival, resulting in 80% of samples growing in culture for at least 1 month and beyond. Overnight refrigeration of samples before culture initiation had little effect on success rates, paving the way for cultures to be established for samples collected over wide geographical areas, such as those for clinical trials. Primary cultures demonstrated good correlation for differentiation markers compared to parent cancers, and were highly dynamic in 3D culture. In Matrigel, many colonies formed central lumens, indicating the presence of stem-like cells. Viable colonies in these cultures recapitulated the in vivo generation of carcinoembryonic antigen (CEA)-positive necrotic/apoptotic debris, much of which was derived from abnormal vacuolated dynamic 'bubble cells' that have not previously been described. Although bubble cells morphologically resembled signet ring cells, a rare cancer subtype, immunostaining suggested that they were most likely derived from terminally differentiated enterocytes. Micro-assays showed that drug toxicity could be measured in these cultures within hours and with sensitivity down to a few hundred cells. Primary cultures derived by our method provide valid in vitro avatars for studying the pathology of cancers in vitro and are amenable to pre-clinical drug testing, paving the way for personalized cancer treatment. Hide abstract
Cancer Res., 74 (12), pp. 3238-47. Read abstract2014. Colorectal cancer cell lines are representative models of the main molecular subtypes of primary cancer.
Human colorectal cancer cell lines are used widely to investigate tumor biology, experimental therapy, and biomarkers. However, to what extent these established cell lines represent and maintain the genetic diversity of primary cancers is uncertain. In this study, we profiled 70 colorectal cancer cell lines for mutations and DNA copy number by whole-exome sequencing and SNP microarray analyses, respectively. Gene expression was defined using RNA-Seq. Cell line data were compared with those published for primary colorectal cancers in The Cancer Genome Atlas. Notably, we found that exome mutation and DNA copy-number spectra in colorectal cancer cell lines closely resembled those seen in primary colorectal tumors. Similarities included the presence of two hypermutation phenotypes, as defined by signatures for defective DNA mismatch repair and DNA polymerase ε proofreading deficiency, along with concordant mutation profiles in the broadly altered WNT, MAPK, PI3K, TGFβ, and p53 pathways. Furthermore, we documented mutations enriched in genes involved in chromatin remodeling (ARID1A, CHD6, and SRCAP) and histone methylation or acetylation (ASH1L, EP300, EP400, MLL2, MLL3, PRDM2, and TRRAP). Chromosomal instability was prevalent in nonhypermutated cases, with similar patterns of chromosomal gains and losses. Although paired cell lines derived from the same tumor exhibited considerable mutation and DNA copy-number differences, in silico simulations suggest that these differences mainly reflected a preexisting heterogeneity in the tumor cells. In conclusion, our results establish that human colorectal cancer lines are representative of the main subtypes of primary tumors at the genomic level, further validating their utility as tools to investigate colorectal cancer biology and drug responses. Hide abstract
Cancer Res., 74 (9), pp. 2377-84. Read abstract2014. Cancer cell lines for drug discovery and development.
Despite the millions of dollars spent on target validation and drug optimization in preclinical models, most therapies still fail in phase III clinical trials. Our current model systems, or the way we interpret data from them, clearly do not have sufficient clinical predictive power. Current opinion suggests that this is because the cell lines and xenografts that are commonly used are inadequate models that do not effectively mimic and predict human responses. This has become such a widespread belief that it approaches dogma in the field of drug discovery and optimization and has spurred a surge in studies devoted to the development of more sophisticated animal models such as orthotopic patient-derived xenografts in an attempt to obtain more accurate estimates of whether particular cancers will respond to given treatments. Here, we explore the evidence that has led to the move away from the use of in vitro cell lines and toward various forms of xenograft models for drug screening and development. We review some of the pros and cons of each model and give an overview of ways in which the use of cell lines could be modified to improve the predictive capacity of this well-defined model. Hide abstract
Br. J. Cancer, 108 (10), pp. 2106-15. Read abstract2013. Myofibroblast activation in colorectal cancer lymph node metastases.
BACKGROUND: Myofibroblasts have an important role in regulating the normal colorectal stem cell niche. While the activation of myofibroblasts in primary colorectal cancers has been previously described, myofibroblast activation in lymph node metastases has not been described before. METHODS: Paraffin-embedded lymph node sections from patients with macrometastases, micrometastases and isolated tumour cells were stained to identify myofibroblasts and to characterise the distribution of different cell types in tumour-containing lymph nodes. The extent of myofibroblast presence was quantified and compared with the size of the metastasis and degree of proliferation and differentiation of the cancer cells. RESULTS: We show substantial activation of myofibroblasts in the presence of colorectal metastases in lymph nodes, which is intimately associated with glandular structures, both in micro- and macrometastases. The degree of activation is positively associated with the size of the metastases and the proportion of Ki67+ve cancer cells, and negatively associated with the degree of enterocyte differentiation as measured by CK20 expression. CONCLUSION: The substantial activation of myofibroblasts in tumour-containing lymph nodes strongly suggests that these metastatic cancer cells are still significantly dependent on their microenvironment. Further understanding of these epithelial-mesenchymal interactions could lead to the development of new therapies in metastatic disease. Hide abstract
Proc. Natl. Acad. Sci. U.S.A., 109 (51), pp. 21046-51. Read abstract2012. Direct and immune mediated antibody targeting of ERBB receptors in a colorectal cancer cell-line panel.
A significant proportion of colorectal cancer (CRC) patients are resistant to anti-ERBB1 [avian erythroblastic leukemia viral (v-erb-b) oncogene homolog, receptor for EGF] monoclonal antibodies (Mabs). We evaluated both immune and nonimmune effects of cetuximab (anti-ERBB1 Mab), trastuzumab (anti-ERBB2 Mab), pertuzumab (anti-ERBB2 Mab), and lapatinib (dual ERBB1 and ERBB2 tyrosine kinase inhibitor) in a large well-characterized panel of 64 CRC cell lines to find response predictive tumor characteristics. There was a significant correlation between the direct effects of cetuximab and lapatinib. Both agents were associated (P = 0.0004) with "triple' wild-type status in KRAS, BRAF, and PIK3CA exon 20. Most cell lines were resistant to the direct effects of anti-ERBB2 Mabs, suggesting that the effects of lapatinib might mainly be through ERBB1. Microarray mRNA expression profiles of sensitive and resistant cell lines showed that although ERBB1 receptor or ligand levels did not associate with cetuximab sensitivity, high levels of ERBB2 (P = 0.036) and amphiregulin (P = 0.026) predicted sensitivity to lapatinib. However, higher ERBB1 expression predicted susceptibility to cetuximab-induced antibody-dependent cellular cytotoxicity and occurred independently of KRAS/BRAF/PIK3CA mutations (P = 0.69). Lapatinib may be an effective alternative therapy to cetuximab in triple wild-type tumors. Microarray analysis provides suggestive biomarkers for resistance. ERBB1 levels, independent of mutation status, predict immune killing. Therefore, anti-ERBB1 antibodies may be considered in CRC tumors with higher ERBB1 expression and favorable FcγR polymorphisms. Hide abstract
Proc. Natl. Acad. Sci. U.S.A., 108 (11), pp. 4382-7. Read abstract2011. Hypoxia and lineage specification of cell line-derived colorectal cancer stem cells.
Hypoxia is an important regulator of normal and cancer stem cell (CSC) differentiation. Colorectal CSCs from SW1222, LS180, and CCK81 colorectal cancer-derived cell lines are able to differentiate into complex 3D lumen-containing structures in normoxia, whereas in hypoxia, they form undifferentiated dense colonies that have reduced expression of the enterocyte differentiation marker CDX1, lack goblet cell formation, and have increased expression of BMI1 and activated Notch1. Hypoxia increases the clonogenicity of CSCs, which is cumulative as each round of hypoxia enriches for more CSCs. The hypoxic phenotype is reversible, because cells from hypoxic-dense colonies are able to reform differentiated structures when regrown in normoxia. We show that CDX1 is able to stimulate the generation of lumens even in hypoxia and has a negative feedback on BMI1 expression. Knockdown of CDX1 reduces lumen formation but does not affect goblet cell formation, suggesting that enterocytes and goblet cells form from different progenitor cells. Notch inhibition by dibenzazepine (DBZ) allowed CSCs to form goblet cells in both normoxia and hypoxia. Finally, we show that Hif1α, but not CA9, is an important mediator of the effects of hypoxia on the clonogenicity and differentiation of CSCs. In summary, hypoxia maintains the stem-like phenotype of colorectal cell line-derived CSCs and prevents differentiation of enterocytes and goblet cells by regulating CDX1 and Notch1, suggesting that this regulation is an important component of how hypoxia controls the switch between stemness and differentiation in CSCs. Hide abstract
Eur. J. Hum. Genet., 20 (2), pp. 203-10. Read abstract2012. People of the British Isles: preliminary analysis of genotypes and surnames in a UK-control population.
There is a great deal of interest in a fine-scale population structure in the UK, both as a signature of historical immigration events and because of the effect population structure may have on disease association studies. Although population structure appears to have a minor impact on the current generation of genome-wide association studies, it is likely to have a significant part in the next generation of studies designed to search for rare variants. A powerful way of detecting such structure is to control and document carefully the provenance of the samples involved. In this study, we describe the collection of a cohort of rural UK samples (The People of the British Isles), aimed at providing a well-characterised UK-control population that can be used as a resource by the research community, as well as providing a fine-scale genetic information on the British population. So far, some 4000 samples have been collected, the majority of which fit the criteria of coming from a rural area and having all four grandparents from approximately the same area. Analysis of the first 3865 samples that have been geocoded indicates that 75% have a mean distance between grandparental places of birth of 37.3 km, and that about 70% of grandparental places of birth can be classed as rural. Preliminary genotyping of 1057 samples demonstrates the value of these samples for investigating a fine-scale population structure within the UK, and shows how this can be enhanced by the use of surnames. Hide abstract
Nature, 491 (7422), pp. 56-65. Read abstract2012. An integrated map of genetic variation from 1,092 human genomes.
By characterizing the geographic and functional spectrum of human genetic variation, the 1000 Genomes Project aims to build a resource to help to understand the genetic contribution to disease. Here we describe the genomes of 1,092 individuals from 14 populations, constructed using a combination of low-coverage whole-genome and exome sequencing. By developing methods to integrate information across several algorithms and diverse data sources, we provide a validated haplotype map of 38 million single nucleotide polymorphisms, 1.4 million short insertions and deletions, and more than 14,000 larger deletions. We show that individuals from different populations carry different profiles of rare and common variants, and that low-frequency variants show substantial geographic differentiation, which is further increased by the action of purifying selection. We show that evolutionary conservation and coding consequence are key determinants of the strength of purifying selection, that rare-variant load varies substantially across biological pathways, and that each individual contains hundreds of rare non-coding variants at conserved sites, such as motif-disrupting changes in transcription-factor-binding sites. This resource, which captures up to 98% of accessible single nucleotide polymorphisms at a frequency of 1% in related populations, enables analysis of common and low-frequency variants in individuals from diverse, including admixed, populations. Hide abstract
Proc. Natl. Acad. Sci. U.S.A., 107 (8), pp. 3722-7. Read abstract2010. Cancer stem cells from colorectal cancer-derived cell lines.
Cancer stem cells (CSCs) are the subpopulation of cells within a tumor that can self-renew, differentiate into multiple lineages, and drive tumor growth. Here we describe a two-pronged approach for the identification and characterization of CSCs from colorectal cancer cell lines, using a Matrigel-based differentiation assay, and cell surface markers CD44 and CD24. About 20 to 30% of cells from the SW1222 cell line form megacolonies in Matrigel that have complex 3D structures resembling colonic crypts. The megacolonies' capacity to self-renew in vitro is direct evidence that they contain the CSCs. Furthermore, just 200 cells from SW1222 megacolonies initiate tumors in NOD/SCID mice. We also showed that CD44(+)CD24(+) cells enriched for colorectal CSCs in the HT29 and SW1222 cell lines, which can self-renew and reform all four CD44/CD24 subpopulations, are the most clonogenic in vitro and can initiate tumors in vivo. A single SW1222 CD44(+)CD24(+) CSC, when grown in Matrigel, can form large megacolonies that differentiate into enterocyte, enteroendocrine, and goblet cell lineages. The HCT116 line does not differentiate or express CDX1, nor does it contain subpopulations of cells with greater tumor-forming capacity, suggesting that HCT116 contains mainly CSCs. However, forced expression of CDX1 in HCT116 leads to reduced clonogenicity and production of differentiating crypt-containing colonies, which can explain the selection for reduced CDX1 expression in many colorectal cancers. In summary, colorectal cancer cell lines contain subpopulations of CSCs, characterized by their cell surface markers and colony morphology, which can self-renew and differentiate into multiple lineages. Hide abstract
J. Theor. Biol., 266 (4), pp. 708-11. Read abstract2010. On the proportion of cancer stem cells in a tumour.
It is now generally accepted that cancers contain a sub-population, the cancer stem cells (CSCs), which initiate and drive a tumour's growth. At least until recently it has been widely assumed that only a small proportion of the cells in a tumour are CSCs. Here we use a mathematical model, supported by experimental evidence, to show that such an assumption is unwarranted. We show that CSCs may comprise any possible proportion of the tumour, and that the higher the proportion the more aggressive the tumour is likely to be. Hide abstract
Curr. Opin. Genet. Dev., 20 (3), pp. 262-7. Read abstract2010. Rare genetic variants and the risk of cancer.
There are good reasons to expect that common genetic variants do not explain all of the inherited risk of the common cancers, not least of these being the relatively low proportion of familial relative risk that common cancer SNPs currently explain. One promising source of the unexplained risk is rare, low-penetrance genetic variants, a class that ranges from low-frequency polymorphisms (allele frequency < 5%) through subpolymorphic variants (frequency 0.1-1.0%) to very low frequency or 'private' variants with frequencies of 0.1% or less. Examples of rare cancer variants include breast cancer susceptibility loci CHEK2, BRIP1 and PALB2. There are considerable challenges associated with the discovery and testing of rare predisposition alleles, many of which are illustrated by the issues associated with variants of unknown significance in the Mendelian cancer predisposition genes. However, whilst cost constraints remain, the technological barriers to rare variant discovery and large-scale genotyping no longer exist. If each individual carries many disease-causing rare variants, the so-called missing heritability of cancer might largely be explained. Whether or not rare variants do end up filling the heritability gap, it is imperative to look for them along side common variants. Hide abstract
Proc. Natl. Acad. Sci. U.S.A., 107 (49), pp. 21058-63. Read abstract2010. Replication error deficient and proficient colorectal cancer gene expression differences caused by 3'UTR polyT sequence deletions.
Replication error deficient (RER+) colorectal cancers are a distinct subset of colorectal cancers, characterized by inactivation of the DNA mismatch repair system. These cancers are typically pseudodiploid, accumulate mutations in repetitive sequences as a result of their mismatch repair deficiency, and have distinct pathologies. Regulatory sequences controlling all aspects of mRNA processing, especially including message stability, are found in the 3'UTR sequence of most genes. The relevant sequences are typically A/U-rich elements or U repeats. Microarray analysis of 14 RER+ (deficient) and 16 RER- (proficient) colorectal cancer cell lines confirms a striking difference in expression profiles. Analysis of the incidence of mononucleotide repeat sequences in the 3'UTRs, 5'UTRs, and coding sequences of those genes most differentially expressed in RER+ versus RER- cell lines has shown that much of this differential expression can be explained by the occurrence of a massive enrichment of genes with 3'UTR T repeats longer than 11 base pairs in the most differentially expressed genes. This enrichment was confirmed by analysis of two published consensus sets of RER differentially expressed probesets for a large number of primary colorectal cancers. Sequence analysis of the 3'UTRs of a selection of the most differentially expressed genes shows that they all contain deletions in these repeats in all RER+ cell lines studied. These data strongly imply that deregulation of mRNA stability through accumulation of mutations in repetitive regulatory 3'UTR sequences underlies the striking difference in expression profiles between RER+ and RER- colorectal cancers. Hide abstract
Proc. Natl. Acad. Sci. U.S.A., 112 (13), pp. E1550-8. Read abstract2015. The CDX1-microRNA-215 axis regulates colorectal cancer stem cell differentiation.
The transcription factor caudal-type homeobox 1 (CDX1) is a key regulator of differentiation in the normal colon and in colorectal cancer (CRC). CDX1 activates the expression of enterocyte genes, but it is not clear how the concomitant silencing of stem cell genes is achieved. MicroRNAs (miRNAs) are important mediators of gene repression and have been implicated in tumor suppression and carcinogenesis, but the roles of miRNAs in differentiation, particularly in CRC, remain poorly understood. Here, we identified microRNA-215 (miR-215) as a direct transcriptional target of CDX1 by using high-throughput small RNA sequencing to profile miRNA expression in two pairs of CRC cell lines: CDX1-low HCT116 and HCT116 with stable CDX1 overexpression, and CDX1-high LS174T and LS174T with stable CDX1 knockdown. Validation of candidate miRNAs identified by RNA-seq in a larger cell-line panel revealed miR-215 to be most significantly correlated with CDX1 expression. Quantitative ChIP-PCR and promoter luciferase assays confirmed that CDX1 directly activates miR-215 transcription. miR-215 expression is depleted in FACS-enriched cancer stem cells compared with unsorted samples. Overexpression of miR-215 in poorly differentiated cell lines causes a decrease in clonogenicity, whereas miR-215 knockdown increases clonogenicity and impairs differentiation in CDX1-high cell lines. We identified the genome-wide targets of miR-215 and found that miR-215 mediates the repression of cell cycle and stemness genes downstream of CDX1. In particular, the miR-215 target gene BMI1 has been shown to promote stemness and self-renewal and to vary inversely with CDX1. Our work situates miR-215 as a link between CDX1 expression and BMI1 repression that governs differentiation in CRC. Hide abstract
Clin. Cancer Res., Read abstract2016. A NOVEL CARCINOEMBRYONIC ANTIGEN T CELL BISPECIFIC ANTIBODY (CEA TCB) FOR THE TREATMENT OF SOLID TUMORS.
PURPOSE: CEA TCB is a novel IgG-based T Cell Bispecific antibody for the treatment of CEA-expressing solid tumors currently in Phase 1 clinical trials (NCT02324257). Its format incorporates bivalent binding to CEA, a head-to-tail fusion of CEA and CD3e binding Fab domains and an engineered Fc region with completely abolished binding to FcγRs and C1q. The study provides novel mechanistic insights into the activity and mode of action of CEA TCB. EXPERIMENTAL DESIGN: CEA TCB activity was characterized on 110 cell lines in vitro and in xenograft tumor models in vivo using NOG mice engrafted with human PBMCs. RESULTS: Simultaneous binding of CEA TCB to tumor and T cells leads to formation of immunological synapses, T cell activation, secretion of cytotoxic granules and tumor cell lysis. CEA TCB activity strongly correlates with CEA expression, with higher potency observed in highly CEA-expressing tumor cells and a threshold of approximately 10,000 CEA binding sites/cell, which allows distinguishing between high- and low-CEA expressing tumor and primary epithelial cells, respectively. Genetic factors do not affect CEA TCB activity confirming that CEA expression level is the strongest predictor of CEA TCB activity. In vivo, CEA TCB induces regression of CEA-expressing xenograft tumors with variable amounts of immune cell infiltrate, leads to increased frequency of activated T cells and converts PD-L1 negative into PD-L1 positive tumors. CONCLUSION: CEA TCB is a novel generation TCB displaying potent anti-tumor activity; it is efficacious in poorly-infiltrated tumors where it increases T cell infiltration and generates a highly-inflamed tumor microenvironment. Hide abstract
Genetics, 199 (2), pp. 267-79. Read abstract2015. Genetic characterization of human populations: from ABO to a genetic map of the British people.
From 1900, when Landsteiner first described the ABO blood groups, to the present, the methods used to characterize the genetics of human populations have undergone a remarkable development. Concomitantly, our understanding of the history and spread of human populations across the earth has become much more detailed. As has often been said, a better understanding of the genetic relationships among the peoples of the world is one of the best antidotes to racial prejudices. Such an understanding provides us with a fascinating, improved insight into our origins as well as with valuable information about population differences that are of medical relevance. The study of genetic polymorphisms has been essential to the analysis of the relationships between human populations. The evolution of methods used to study human polymorphisms and the resulting contributions to our understanding of human health and history is the subject of this Perspectives. Hide abstract