Primer on Human Pedigree Analysis:

Transcription

1 Primer on Human Pedigree Analysis: Criteria for the selection and collection of appropriate Family Reference Samples John V. Planz. Ph.D. UNT Center for Human Identification Successful Missing Person ID Missing persons identification is driven by the Family Reference Samples Law enforcement is primary point of contact for families Strategy for sample collection is critical How do you know who to collect Understanding genetics of relationship Level of relatedness First Order Second Order Tertiary 1

2 First Order Relative A direct descendant or predecessor of Missing Person SPOUSE - Not a Biological Relative but Critical to evaluation Second Order Relative A direct descendant or predecessor of a First Order Relative Tertiary Relatives Mostly, cousins descendants of Second Order Relatives 2

3 What genetic technologies are used Primary sorting- Lineage Specific Markers These markers are used to associate DNA obtained from a set of unidentified remains to reference individuals along Maternal and Paternal lines INSIST that mtdna is run on your samples when appropriate!! Maternal Lineages Mitochondrial DNA (mtdna) is transferred along the Maternal line Paternal Lineages Y Chromosome markers are transferred along the Paternal line 3

4 Autosomal Markers The DNA most folks talk about diffuses as you move away from the source Target for collection First Order Priority 1!! Both parents of Missing Person One parent and two or more Siblings One parent, Spouse and one or more children of Missing Person One parent and one sibling (might throw in an aunt or uncle too) Two or more siblings Both parents of Missing Person ab cd ac This is a slam dunk! One type from Mom and one from Dad must match the remains at every marker tested mtdna from Mom Y STR from Dad 4

5 One parent and Siblings ab cd bd ac ac One type from Mom must match the remains at every marker tested and so does mtdna A brother will share the Y STR type from Dad With Mom and the sibs we may possibly reconstruct what Dad might have been. One parent, spouse and children ab ab a/b ac de ce cd One type from Mom must match the remains at every marker tested and so does mtdna A son will share the father s Y STR type With Mom and the kids we may possibly reconstruct what Dad must have. One parent, one sibling and Uncle One type from Mom must match the remains at every marker tested and so does mtdna An Uncle will share the Y STR type from Dad Sister may share types with Missing Person and will identify one type from Dad Uncle may help here too maybe 5

6 What about siblings Siblings will share the mother s mtdna Brothers will share the fathers Y STR type Siblings generally share some autosomal markers but they don t have to! Enough siblings could reconstruct the parents IF they are Full Siblings! What about siblings who are not Reality some folks just don t know Test Brothers for shared Y STR type Test Siblings for shared mtdna type Known Half-siblings are helpful with the lineage specific markers but worthless with the autosomal markers So, what is needed Target First Order Relatives Need minimum of 2, better yet 3 family reference samples Represent both Maternal and Paternal Lineages Don t bother with distant relative except for a lineage specific markers Don t bother with direct samples i.e toothbrush, combs, underwear, etc 6

7 What s wrong with the direct samples Largely unreliable Must be proofed out with family reference samples Many result in DNA mixtures True Known samples: Guthrie Card, tissue biopsy, Military DNA repository sample card Identifications can be made if the right samples go into the database nothing happens if they don t! Now we will look at what you get back when an association is made for one of your cases and what it means. Each case is unique! Many scenarios can exist, and in each case the assumptions being made should be clearly stated. Lets look at a simple one: Scenario: Reference samples available from a mother and son of a missing person. Bones of a male are submitted as unidentified remains. 7

8 Reference Samples Unidentified Remains Metadata: Anthropology Sex Dental What can unite these cases Reference Samples = Unidentified Remains mtdna Reference Samples Unidentified Remains = Y STRs 8

9 Reference Samples P D Unidentified Remains B C Autosomal STRs Hypotheses: H o : The remains are from the missing person H a : The remains are unrelated to pedigree Hypotheses: H o : The remains are from the missing person H a : The remains are unrelated to pedigree These hypotheses allow for additional statistical understanding: we can calculate a probability associated with each hypothesis since the genetic markers are quantitative markers we won t bore you with the math When we look at these two hypotheses one may be more strongly supported than the other based on the data obtained in the case. All we really do at this point is compare the probabilities associated with each hypothesis and see which is favored. Or which scenario is more Likely. 9

10 For something like our example we might have the following conclusion: Given the genetic data and scenario proposed, it is approximately 10 times more likely to observe these results if the remains originated from the missing individual rather than the remains representing an individual unrelated to the pedigree examined. If we included the mtdna and Y STR data it would increase the likelihood substantially since in most cases these haplotypes have very small frequencies in the population. If we include all 13 STR markers we routinely test, the likelihood also increases substantially. But if we add another relative. quantum leaps at all levels For our example Pedigree M, C 1 10 Kinship Index M, S, C 1 20 M, S, C 1, C 2 40 M, S, C 1, C 2 20 The KI has a range of >0 to infinity So what is meaningful 10

11 So what is meaningful Comparison of UHR to a single sibling KI~0.8 Same UHR to both parents KI~385 Billion Same UHR to a direct blood sample ~ 43 Trillion Comparison of UHR to a mother & sibling KI~10K Same samples with mtdna KI~0 excluded! UHR to two siblings (13 STRs) KI~105 UHR to two siblings ( 6 STRs) KI~10,200 While the success and statistical relevance rests with how good a pedigree you have to compare to, the remains sample is still the limiting factor. We have good 2 lineage specific markers CODIS STRs have limited it statistical ti ti strength mtdna works extremely well on compromised samples insist that it is done!! Better markers are on the horizon When a lab sends out a report on a putative association, they put the ball in your court! Call them if you have questions Let them know if other relatives are available Let them know if an ID is rendered Let them know if a suspect is developed! They do care! 11