Identity testing

lecture 3

What is a polymorphism?

DNA sequences that differ from the sequences in a population, but can still be shared within the population

What is VNTR?

variable number of tandem repeats

• 10-50 bp lengths of repeats

  • aka minisatellites

How can we analyze VNTR?

RFLP analysis

If we are testing two individuals for shared alleles, how is the chance of sharing influenced?

each additional gene tested will decrease the chance of sharing by 10-fold

How did we used to perform parentage testing?

RFLP between the child and alleged parents

What difference in alleles can exclude an alleged father from paternity?

just one allele

How many loci must be tested for parentage?

at least 8

What is STR?

short tandem repeats

• <10 bp repeats

  • microsatellites

How can we analyze STRs?

with PCR

Can we use fragmented or degraded DNA to detect STRs?

Yes

Which techniques can be used to analyze STRs in identity tests?

capillary electrophoresis with fluorescent markers

What kind of identification is commonly done with STR analysis? What gene is targeted?

gender ID
- test for amelogenin gene

Where is the amelogenin gene located?

the X and Y chromosomes

With STR analysis, how many bands would we expect from an XY individual when looking at the amelogenin gene?

two bands

→ Y chromosome amelogenin gene is 6 bp longer than X, so it produces a fragment at a different size

With STR analysis, how many bands would we expect from an XX individual when looking at the amelogenin gene?

one

How is confidence of an identity match influenced with increasing allele determination?

increased

In criminal ID cases, what system is used?

CODIS

In the CODIS system, how many core loci are used to ID?

13

What is a paternity index?

the likelihood that a child’s allele is inherited from the alleged father rather than random chance

What kind of paternity index does a common allele have?

low

What kind of paternity index does a rare allele have?

high

What is a combined paternity index?

multiplied paternity indexes for various alleles that state the likelihood of inheritance rather than random chance

What shape is the mitochrondrial genome?

circular

How is mitochondria DNA inherited?

from the mother

What are the uses of mtDNA?

• if our nuclear DNA is insufficient

  • good for identifying missing people, or ancestral relatives

What are the two main purposes for using DNA fingerprinting?

forensics and ancestral searching

What is the chain of events in inspecting criminal evidence?

1. visual inspection

2. presumptive tests (is it really evidence)

3. confirmatory tests

4. reporting to authorities

What are some sources of biological evidence?

blood, saliva, urine, hair, teeth, bone, tissue

• also cigarettes, envelopes, kleenex, bedsheets, clothing