US10114922B2

US10114922B2 - Identifying ancestral relationships using a continuous stream of input

Info

Publication number: US10114922B2
Application number: US14/029,765
Authority: US
Inventors: Jake Kelly Byrnes; Aaron Ling; Keith D. Noto; Jeremy Pollack; Catherine Ann Ball; Kenneth Gregory Chahine
Original assignee: Ancestry com DNA LLC
Current assignee: Ancestry com DNA LLC
Priority date: 2012-09-17
Filing date: 2013-09-17
Publication date: 2018-10-30
Also published as: US20160026755A1; US20190139624A1; US11335435B2

Abstract

Identification of inheritance-by-descent haplotype matches between individuals is described. A set of tables including word match, haplotypes and segment match tables are populated. DNA samples are received and stored. A word identification module extracts haplotype values from each sample. The word match table is indexed according to the unique combination of position and haplotype. Each column represents a different sample, and each cell indicates whether that sample includes that haplotype at that position. The haplotypes table includes the raw haplotype data for each sample. The segment match table is indexed by sample identifier, and columns represent other samples. Each cell is populated to indicate for each identified sample pair which position range(s) include matching haplotypes for both samples. The tables are persistently stored in databases of the matching system. As new sample data is received, each table is updated to include the newly received samples, and additional matching takes place.

Description

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional applications 61/702,160 filed on Sep. 17, 2012 and 61/874,329 filed on Sep. 5, 2013, both of which are hereby incorporated by reference in their entirety.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Oct. 16, 2013, is named 24437US_CRF_sequencelisting.txt and is 1,462 bytes in size.

BACKGROUND Field

The disclosed embodiments relate to identifying individuals in an existing dataset of genetic information that are related to individuals whose genetic information is newly analyzed.

Description of Related Art

Although humans are, genetically speaking, almost entirely identical, small differences in our DNA are responsible for much of the variation between individuals. Stretches of DNA that are determined to be relevant for some purpose are referred to as haplotypes. Haplotypes are identified based on consecutive single nucleotide polymorphisms (SNPs) of varying length. Certain haplotypes shared by individuals suggests a familial relationship between those individuals based on a principal known as identity-by-descent (IBD).

Because identifying segments of IBD DNA between pairs of genotyped individuals is useful in many applications, numerous methods have been developed to perform IBD analysis (Purcell et al. 2007, Gusev et al. 2009, Browning and Browning 2011, Browning and Browning 2013). However, these approaches do not scale for continuously growing very large datasets. For example, the existing GERMLINE implementation is designed to take a single input file containing all individuals to be compared against one another. While appropriate for the case in which all samples are genotyped and analyzed simultaneously, this approach is not practical when samples are collected incrementally.

SUMMARY

Described embodiments enable identification of IBD and consequently familial relationships within received samples and between a received sample and samples in an existing data set. An initial configuration includes populating a set of tables including a word match table, a haplotypes table and a segment match table. A set of phased DNA samples are received, e.g., from a DNA service, and stored in a DNA database. A word identification module extracts haplotype values from each sample. The word match table is indexed in one embodiment according to haplotypes, for example a specific haplotype on a specific chromosome. Each column of the word match table represents a different sample, and each cell includes an indication of whether that sample includes that haplotype at that position. The haplotypes table is populated to include the raw haplotype data for each sample. The segment match table is indexed by sample identifier, and columns represent other samples. Each cell of the table is populated to indicate for each identified sample pair which position range(s) include matching haplotypes for both samples.

The tables are persistently stored in databases of the matching system. Subsequently, as new sample data is received, each of the tables is updated to include the newly received samples, and additional matching takes place. The persistence of the tables avoids the necessity of recomputing relationships with the addition of each new sample, thus allowing for rapid and efficient scaling of the identification system and accommodation of continuous or periodic input of new sample data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a system architecture and environment in accordance with one embodiment.

FIG. 2 illustrates an example of a word match table according to one embodiment. FIG. 2 discloses SEQ ID NOS 2-5, respectively, in order of appearance.

FIG. 3 illustrates an example of a haplotype table in accordance with one embodiment. FIG. 3 discloses SEQ ID NOS 2-3, 6, 2-3, 6-7 and 3-4, respectively, in order of appearance.

FIG. 4 illustrates an example of a segment match table in accordance with one embodiment.

FIG. 5 illustrates a process for processing new samples in accordance with one embodiment.

FIG. 6 illustrates a process for updating a word match table in accordance with one embodiment.

FIG. 7 illustrates a process for updating a segment match table in accordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of the architecture and environment of system 100 according to one embodiment. System 100 includes a word identification module 103, a word match database 107, a segment match database 109, a haplotype database 111, and a DNA database 113. Also depicted in FIG. 1 are individual 101 (i.e. a human or other organism), DNA extraction service 102, and a DNA quality control (QC) and matching preparation service 115. Each of these illustrated features is described further below. Note that for purposes of clarity, only one of each item is included in the figure, but when implemented multiple instances of any or all of the depicted modules may be employed, as will be appreciated by those of skill in the art.

System 100 may be implemented in hardware or a combination of hardware and software. For example, system 100 may be implemented by one or more computers having one or more processors executing application code to perform the steps described here, and data may be stored on any conventional storage medium and, where appropriate, include a conventional database server implementation. For purposes of clarity and because they are well known to those of skill in the art, various components of a computer system, for example, processors, memory, input devices, network devices and the like are not shown in FIG. 1. In some embodiments, a distributed computing architecture is used to implement the described features. One example of such a distributed computing platform is the Apache Hadoop project available from the Apache Software Foundation.

Individuals 101 provide DNA samples for analysis of their genetic data. In one embodiment, an individual uses a sample collection kit to provide a sample, e.g., saliva, from which genetic data can be reliably extracted according to conventional methods. DNA extraction service 102 receives the sample and genotypes the genetic data, for example by extracting the DNA from the sample and identifying values of single nucleotide polymorphisms (SNPs) present within the DNA. DNA QC and matching preparation service 115 phases the genetic data and assesses data quality by checking various attributes such as genotyping call rate, genotyping heterozygosity rate, and agreement between genetic and self-reported gender. System 100 receives the genetic data from DNA extraction service 102 and stores the genetic data in DNA database 113.

Initial Configuration

For ease of explanation, we assume an initial set of DNA samples have been collected and are stored in DNA database 113. A decision for the implementer is to select a segment or window length to be used by system 100. In practice, window sizes of 100 or more SNPs are appropriate, but for purposes of illustration here we assume without loss of generality a window size of 10 SNP markers. The value of each marker will be one of two genetic bases, and each individual is associated with two sequences of values called haplotypes, because each person has two copies of each chromosome. For example, the genetic data for individual 1, haplotype 1, markers 1 through 10 might be: GCCATATGGC (SEQ ID NO: 1).

In processing the initial samples, word identification module 103 and matching module 105 populate an initial set of tables that we refer to below as the word match table, haplotypes table and segment match table. In the illustrated embodiment, the word match table is stored in word match database 107; the haplotypes table is stored in haplotype database 111; and the segment match table is stored in segment match database 109.

FIG. 2 illustrates a word match table 202 according to one embodiment. Word identification module 103 obtains genetic data for an individual from DNA database 113 and uses the data to populate the table. In one embodiment, each row of word match table 202 specifies a haplotype observed in a particular genomic window, and each column specifies an individual (referred to interchangeably as a user). A table cell (i.e. a particular row/column combination) therefore indicates whether that user has that haplotype, and reading across a row enables identification of all such users with the haplotype. In various embodiments, the haplotypes are hashed prior to insertion into the table 202. Depending on the window size and number of samples, this table may be very large. However, it is also very sparse as each individual has at most two distinct haplotypes for each window. Distributed, scalable big data stores such as Apache HBase are particularly well suited to storing and querying very large, very sparse tables such as this. In one embodiment, the row keys for word match table 202 are of the form [CHROMOSOME] [POSITION] [HAPLOTYPE], where [CHROMSOME] and [POSITION] denote the unique genomic location of the first SNP in a particular window and [HAPLOTYPE] is the sequence of bases observed in this window.

For example, referring still to FIG. 2, a row key of the form chr1_0000000010_ACTACGACCA (SEQ ID NO: 2) refers to the haplotype ACTACGACCA (SEQ ID NO: 2) observed in the window beginning at the 10^thSNP on chromosome 1. Executing a “Get” operation against the Window Match table with this key returns a list of all users having that haplotype at that position, which could be, for example, the following collection of columns:

U₁, U₅, U₇.

This indicates that samples U₁, U₅, and U₇have at least one copy of that haplotype in this window on this chromosome. Word identification module 103 adds a new row to table 202 each time a haplotype is observed for a first time at a particular window on a particular chromosome, and adds an indicator to each user's column if that user's sample includes the presence of that haplotype.

Referring now to FIG. 3, word identification module 103 also populates a haplotype table 302 with the raw phased haplotype data for each window and each sample. The row keys for haplotype table 302 are of the form [CHROMOSOME] [USER ID]. The columns in haplotype table 302 represent the pair of haplotypes observed in each window for the specified sample and chromosome. Each column is indexed by [POSITION] [EVEN OR ODD]. In the illustrated embodiment, the position is the first base in that particular window as numbered from the beginning of the sequence of nucleic acids for that sample. The value for each cell is the sequence for the specified sample at the given chromosome and position. When populating the table with new data, word identification module 103 arbitrarily labels each chromosomal haplotype pair as ODD or EVEN, thus while these definitions are consistent between neighboring windows on the same chromosome, there is no relationship between different chromosomes of the same individual. In the example illustrated in FIG. 3, the row key is of the form Chr1_U₁. This key would return all haplotype data for each window for sample U₁on chromosome 1. Storing the sequence of each window is useful for fuzzy matches between individuals after exact matches have been determined, as described further below. Word identification module 103 in the illustrated embodiment continues to add rows for each user and each chromosome until all of the initial samples are reflected in haplotypes table 302.

Next, and referring now to FIG. 4, matching module 105 populates the segment match table 402 to identify individuals who have at least one haplotype in common at a given location. Matching module 105 uses data from the word match table 202 as well as the haplotype table 302. These pairs of individuals are stored in the segment match database 109. The operation of the matching module 105 is discussed in greater detail below.

FIG. 4 illustrates a segment match table 402 according to one embodiment. Each row index represents a specific user and chromosome combination. Each column represents an individual and each cell contains a coordinate array indicating the locations of matching segments on that chromosome between the specified pair of individuals. In various embodiments, only matching segments of at least a threshold length, e.g., 5 Mb, 1 cM, etc., as determined by the implementer, are considered a match for purposes of insertion into table 402. The row key for this table in the illustrated embodiment is of the form [CHROMOSOME] [USER ID]. In the first row of FIG. 4, the row key Chr1_U₁specifies the row containing matches for user 1 along chromosome 1. Performing a “Get” operation against the segment match table 402 with key Chr1_U₁returns column U₂for user 2 as well as other users with whom user 1 has segments in common. For example, the operation might return:

U₂, U₄, U₅₃₈, U₇₀₃₄,

indicating that the sample with ID U1 has segments in common with samples U₂, U₄, U₅₃₈, and U₇₀₃₄.

The cell for U₂might contain values 10-40, 120-130, 550-700, 800-4560, indicating that along chromosome 1, for segment ranges 10-40, 120-130, 550-700, 800-4560 samples U₁and U₂contain at least one haplotype that is identical or nearly identical.

Matching module 105 proceeds to populate the segment match table 402 for each user and each chromosome. In one embodiment, a fuzzy matching algorithm is used to extend identified matches between the haplotypes of two users. For example, suppose that within chromosome 1, U₁has an exact segment matching with U₅₃₂from SNPs 100-299. Matching module 105 executes a fuzzy extension process that attempts to extend this match on both sides while allowing for small numbers of unmatched bases. To extend this segment on the left flank, matching module 105 performs a “Get” call against haplotypes table 302, supplying the row keys chr1_U₁and chr1_U₅₃₂, requesting the following columns:

0000000000_E, 0000000000_O, 0000000010_E, 0000000010_O . . . 0000000090_E, 0000000090_O.

The cells of this table contain the actual haplotypes for these windows and matching module 105 can extend a match by locating the sites containing alternate homozygotes (e.g., T/T for one sample and G/G for the other). Depending on the parameters specified by the implementer, fuzzy match extension proceeds until x alternate homozygotes are encountered. This process is repeated for each flank of each segment, updating the appropriate cells in segment match table 402 to reflect the longer matching string. Matching module 105 proceeds to populate the segment match table 402 for each user and each chromosome.

Addition of New Samples

After the initial population of tables 302, 202 and 402 in their respective databases 111, 107, 109 by word identification module 103 and matching module 105, new samples from additional individuals 101 can be received, and relationships between those individuals and both the previously processed individuals and other new individuals can be determined as described below.

Referring to FIG. 5, a process for processing new samples can be described generally as follows. A new sample is received 502 and stored in DNA database 113 as described above. Word match table 202 is updated 504, haplotypes table 302 is updated 506, and segment match table 402 is also updated 508 to reflect the newly identified relationships. We describe each of these processes in turn.

Referring to FIG. 6, word identification module 103 obtains 602 the new sample data, e.g., from DNA database 113. Word identification module 103 then updates the word match table 202, which, as noted, is persistently stored in database 107. To update the table 202, word identification module 103 first adds 604 a column to the world table to accommodate values for the new user. Next 606, for each haplotype in the user sample, identification module 103 determines 608 whether that haplotype is already in table 202. If not, module 103 adds 610 a new row for the table. Once the appropriate row is added or found, module 103 updates the user's column to indicate 612 the presence of the haplotype in the user's sample. The process then repeats 606 for each haplotype and for each newly received sample. The updated word match table 202 remains stored in database 107.

Next, word identification module 103

updates

506 haplotypes table 302 by adding a new row for each chromosome of the new user sample, and inserting the relevant haplotype data for each window.

In one embodiment, word identification module 103

updates

504, 506 the word match and haplotypes tables for each new sample being processed in a current batch, and then matching module 105

updates

508 the segment match table 402. Referring to FIG. 7, matching module 105 obtains 702 the new sample data and adds 704 a column to segment match table 402 for the new user. Next 706, for each chromosome of the new user, in an embodiment such as the one illustrated in FIG. 4 in which each row represents a particular chromosome for a particular user, matching module 105 adds 707 a row to segment match table 402. Then 708, for each of the existing users with data in table 402, matching module 105 determines 710 whether any haplotype matches of a minimum threshold length exist between the new user's sample and the existing user's sample on that chromosome. If so, matching module 105 extends 712 the match where possible, using a fuzzy logic approach described above, and enters 714 the results of the match in the appropriate cell of table 402. This process then continues, matching the new user against each existing user across each chromosome.

In one embodiment, following the update procedure of FIG. 5, a reducer is executed that eliminates duplicate matches due to reciprocal comparisons and creates an output file with the results from the process run. The data in the file is then usable to inform the implementer about potential relationships due to IBD between the various user samples. In some embodiments, system 100 is implemented as part of a service that enables subscribing users to submit samples and receive reports about other subscribers to whom they may be related, for example for those users who share a sufficiently high number of haplotype matches as described above. Depending on a user's privacy settings and opt-in preferences, examples of information provided might include blind (anonymous) introductions, account identifiers, or names or other contact information.

In addition to the embodiments specifically described above, those of skill in the art will appreciate that the invention may additionally be practiced in other embodiments. Within this written description, the particular naming of the components, capitalization of terms, the attributes, data structures, or any other programming or structural aspect is not mandatory or significant unless otherwise noted, and the mechanisms that implement the described invention or its features may have different names, formats, or protocols. Further, the system may be implemented via a combination of hardware and software, as described, or entirely in hardware elements. Also, the particular division of functionality between the various system components described here is not mandatory; functions performed by a single module or system component may instead be performed by multiple components, and functions performed by multiple components may instead be performed by a single component. Likewise, the order in which method steps are performed is not mandatory unless otherwise noted or logically required. It should be noted that the process steps and instructions of the present invention could be embodied in software, firmware or hardware, and when embodied in software, could be downloaded to reside on and be operated from different platforms used by real time network operating systems.

Algorithmic descriptions and representations included in this description are understood to be implemented by computer programs. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules or code devices, without loss of generality.

Unless otherwise indicated, discussions utilizing terms such as “selecting” or “computing” or “determining” or the like refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system memories or registers or other such information storage, transmission or display devices.

The present invention also relates to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, DVDs, CD-ROMs, magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, application specific integrated circuits (ASICs), or any type of media suitable for storing electronic instructions, and each coupled to a computer system bus. Furthermore, the computers referred to in the specification may include a single processor or may be architectures employing multiple processor designs for increased computing capability.

The algorithms and displays presented are not inherently related to any particular computer or other apparatus. Various general-purpose systems may also be used with programs in accordance with the teachings above, or it may prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description above. In addition, a variety of programming languages may be used to implement the teachings above.

Finally, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention.

Claims

We claim:

1. A computer-implemented method comprising:

receiving a first set of genetic data, the first set including a plurality of genetic data samples from a first plurality of human individuals, the first set of genetic data including a set of haplotypes for each of the first plurality of human individuals;

for each sample in the first set:

for each of the haplotypes in the sample, storing an identifier of the sample in an entry of a first table having rows indexed by haplotype, the entry located in a row indexed by the haplotype in the sample;

storing in a second table a plurality of haplotypes included in the sample, the second table having rows indexed by segments of each individual;

identifying a set of ranges of haplotype matches between the sample and each other sample based on the haplotypes;

storing in a third table the ranges of haplotype matches between the sample and each other sample, the third table indexed by segments of each individual;

receiving a second set of genetic data, the second set including a plurality of genetic data samples from a second plurality of human individuals, the second set of genetic data including a set of haplotypes for each of the second plurality of human individuals;

for each sample in the second set:

for each of the haplotypes in the sample, updating the first table by including an identifier of the sample in the second set in a row of the first table indexed by the haplotype contained by the sample;

updating the second table by including one or more additional rows each identifying a segment of the sample, wherein each additional row includes a plurality of haplotypes included in the segment;

for each segment of the sample:

identifying ranges of haplotype matches between the segment and each other sample from the first received set and the second received set by:

accessing a subset of haplotypes included in the additional row from the updated second table, and

for each haplotype in the subset of accessed haplotypes:

identifying an initial haplotype match by accessing an identifier of the other sample stored in a common row of the updated first table, the common row indexed by the haplotype in the subset;

accessing a row of the updated second table indexed by the segment of the other sample that is identified by the accessed identifier, the accessed row comprising the haplotype and an adjacent haplotype next to the haplotype; and

extending the initial haplotype match along nucleotide bases of the adjacent haplotype in the accessed row of the updated second table; and

generating a range of haplotype matches between the segment of the sample and the other sample, the range of haplotype matches comprising extended initial haplotype matches across the haplotypes in the subset;

updating the third table by including an additional row indexed by the segment of the sample to include the ranges of haplotype matches between the segment of the sample and each other sample; and

providing to at least two of the first or second plurality of human individuals an indication that a number of haplotype matches between them exceeds a threshold number of matches.

2. The method of claim 1 wherein updating the first table further comprises:

determining that the haplotype is not in the first table; and

adding an additional row in the first table indexed by the haplotype.

3. The method of claim 1 wherein a range of haplotype matches between two samples of the first or second sets comprises matching segments of the haplotypes from those samples of at least a threshold length.

4. The method of claim 1 wherein the first table is indexed by a hash value of the haplotype and updating the first table further comprises:

identifying a haplotype in the sample;

hashing the haplotype;

identifying in the first table a row indexed by the hashed haplotype; and

storing the identifier of the sample in the row of the first table that is indexed by the hashed haplotype.

5. A non-transitory computer readable medium including instructions configured to cause a processor to execute steps comprising:

for each sample in the first set:

for each sample in the second set:

for each segment of the sample:

for each haplotype in the subset of accessed haplotypes:

6. The non-transitory computer readable medium of claim 5 wherein updating the first table further comprises:

determining that the haplotype is not in the first table; and

adding an additional row in the first table indexed by the haplotype.

7. The non-transitory computer readable medium of claim 5 wherein a range of haplotype matches between two samples of the first or second sets comprises matching segments of the haplotypes from those samples of at least a threshold length.

8. The non-transitory computer readable medium of claim 5 wherein the table is indexed by a hash value of the haplotype and updating the first table further comprises:

identifying a haplotype in the sample;

hashing the haplotype;

identifying in the first table a row indexed by the hashed haplotype; and

9. The method of claim 3 wherein the threshold length is at least 1 centimorgan.

10. The non-transitory computer readable medium of claim 7 wherein the threshold length is at least 1 centimorgan.

11. The non-transitory computer readable storage medium of claim 5 wherein a haplotype is a haplotype value, a haplotype value representing particular genetic data present in a particular genomic window.

12. The non-transitory computer readable storage medium of claim 5, wherein the first table comprises a column for storing identifiers of samples, wherein a presence of an identifier of a sample in an entry at an intersection of the column and a row indexed by a haplotype indicates that the sample includes the haplotype that indexes the row.

13. The non-transitory computer readable storage medium of claim 5, wherein the second table comprises a column for each of a plurality of genomic windows; and wherein an entry at each row and column location in the second table indicates the haplotype for the sample of that row and for the genomic window of that column.

14. The non-transitory computer readable storage medium of claim 5, wherein the third table comprises a column for each of the samples; and wherein an entry at each row and column location in the third table indicates the range of haplotype matches generated between a segment of the sample of that row and the sample of that column.

15. The non-transitory computer readable storage medium of claim 5, wherein a range of haplotype matches includes a plurality of haplotype values that are sequential in position within or between genomic windows.

16. The method of claim 1 wherein a haplotype is a haplotype value, a haplotype value representing particular genetic data present in a particular genomic window.

17. The method of claim 1, wherein the first table comprises a column for storing identifiers of samples, wherein a presence of an identifier of a sample in an entry at an intersection of the column and a row indexed by a haplotype indicates that the sample includes the haplotype that indexes the row.

18. The method of claim 1, wherein the second table comprises a column for each of a plurality of genomic windows; and wherein an entry at each row and column location in the second table indicates the haplotype for the sample of that row and for the genomic window of that column.

19. The method of claim 1, wherein the third table comprises a column for each of the samples; and wherein an entry at each row and column location in the third table indicates the range of haplotype matches generated between a segment of the sample of that row and the sample of that column.

20. The method of claim 1, wherein a range of haplotype matches includes a plurality of haplotype values that are sequential in position within or between genomic windows.

21. The method of claim 1,

wherein identifying the initial haplotype match comprises identifying a match between the haplotype in the subset and a haplotype from one sample from either the first or second received set based on an inclusion of an identifier of the sample and an inclusion of an identifier of the one sample in the common row indexed by the haplotype of the updated first table;

wherein identifying ranges of haplotype matches between the segment of the sample and each other sample from the first received set and the second received set further comprises, for each haplotype in the subset, determining whether a nucleotide base of the adjacent haplotype beyond a first flank of the haplotype matches a corresponding sequence beyond a first flank of a haplotype in the accessed row of the updated second table; and

wherein extending the initial haplotype match comprises extending the identified match to an extended genomic window responsive to determining that the sequence beyond the first flank of the haplotype in the subset matches the corresponding sequence beyond a first flank of the haplotype in the accessed row of the updated second table.

22. The non-transitory computer readable storage medium of claim 5, wherein identifying the initial haplotype match comprises identifying a match between the haplotype in the subset and a haplotype from one sample from either the first or second received set based on an inclusion of an identifier of the sample and an inclusion of an identifier of the one sample in the common row indexed by the haplotype of the updated first table;