2 Person Mixture #2

Vaginal swab of Victim

Case Scenario

• Assault occurred in dorm room• Suspect says it was consensual• No other parties heard or saw anything• Victim and Suspect were seen together earlier

that evening• Evidence is the vaginal swab of Victim• Sperm seen on swab

The Egram

This mixture is…

1 2 3 4

25% 25%25%25%1. 50/50 so we can’t do much

2. 50/50 but intimate sample so assume V and deconvolute

3. Just do a LR4. Perfect for CPI

The Interpretation

• This time it’s much closer to a 50/50 mixture• (Mixture #1 we looked at had the foreign

profile as a 65/35 major)• No alleles <300, so no concern about allelic

drop out

The Data Table

Match to Victim

• Remember, it’s her own swab so this is a good QA/QC check if she’s included

• I usually point out that this is a good start to the analysis when I’m on the witness stand

Any Alleles Foreign to Victim?

• We have a quick easy “Find Foreign to Reference” Function

• Red highlights means there are alleles present that are not found in the profile of the Victim

Match to Suspect

• If the suspect is excluded, I’m done• For sake of this demonstration, we’ll check

now• Remember, this shouldn’t influence your stat

The “Auto-Graph”There are 8 loci that the foreign type has only one option so we see those graphed here as we start.

The Victim is a slight major on her own swab, but TPOX and FGA are troublesome.

Problem?The major/minor ratio has flipped at TPOX and FGA.

We’ll come back to these at the end.

CSF Has Two Options for ForeignOption one has the foreign type as 11, 11 and only accounts for 23% of the DNA. Also, that option means the Victim has a PHR of 55%.

Option 2 has the foreign as 11, 12 with a proportion of 46% and both donors’ PHR at 98%.

Option 2 is the better choice

I used the “right click” option to send the 11, 12 to the “Vaginal Foreign” profile.

CSF Has Two Options for ForeignI could have used the “Popout calls” box and seen in real time that an 11 homozygote foreign gives proportions that are all out of whack.

D13 Has Two Options for Foreign

Option 1 is a homozygote foreign, but it doesn’t fit our graph real well, and has a 52% PHR for the Victim. We don’t typically see PHR that poor above 500 rfu

D13 Has Two Options for Foreign

Option 2 is a heterozygous foreign type of 11, 12. This both looks better on the graph, and is in line with what our running average shows us.

Skipping Ahead….For all of the remaining loci we had the same choice between a homozygote unknown and a heterozygote unknown.

In each instance, I selected the heterozygote option.

But we still have FGA and TPOX to deal with

FGAAt FGA we have a peak foreign to Victim in a stutter position.

Let’s recalculate for stutter. FGA = 17% stutter

FGA

Before we correct for stutter, the foreign type is the major contributor.

After we correct for stutter, the foreign type is now the minor contributor.

TPOXCan we fix TPOX by correcting for stutter? Unfortunately, no. This is the only type that fits our validated expectations, so we’ll keep it.

Moral of the story: We deal with biology here. Remember, it’s based on “Random Breeding” and this amplification has a certain amount of randomness in it.

That’s why you get differences between replicate amps.

Final Result

• The profile we deconvoluted matches the foreign profile on the vaginal swab