STRs used for Forensics

Question 1

Satellite

Answer 1

tandemly repeated DNA sequence that contains 1 to 1000s base pairs

Question 2

Satellite location

Answer 2

near the centromere

Question 3

Minisatellite

Answer 3

VNTR
10-100 base pair repeats
Problem: huge range in size making it hard to multiplex

Question 4

Microsatellite

Answer 4

STR
2-6 base pair repeats
make up about 3% of the genome
more than 1 million in the genome

Question 5

Ways to find STRs

Answer 5

search GenBank (6+ contiguous repeat units)
Molecular Biology Isolation

Question 6

Simple repeats

Answer 6

repeats same sequence and length

Question 7

Compound repeats

Answer 7

multiple simple repeats

Question 8

Complex repeats

Answer 8

several repeat blocks with intervening sequences

Question 9

Complex hypervariable repeats

Answer 9

differ in size and sequence

Question 10

Microvariants

Answer 10

contain incomplete repeat units

Question 11

Advantages of tetra nucleotide loci

Answer 11

multiplexing, reduced allelic dropout, used of degraded DNA, reduced size of stutter

Question 12

Naming alleles rules

Answer 12

standardized by International Society of Forensic Genetics (ISFG)
use first possible motif
use the coding strand, or the first published
name micro variants with decimal

Question 13

Selection criteria for STRs

Answer 13

greater than 70% heterozygosity
different chromosomes
reproducible, useful in multiplex
low stutter
low mutation rate
90-500 base pairs

Question 14

Reasons for the 13 CODIS STR loci

Answer 14

different chromosomes (prevent linkage)
15-82 different alleles
simple, compound, and complex
associated with genes or not

Question 15

Commercial kits for STR

Answer 15

labeled primers (ready for multiplexing)
size standard
allelic ladders
buffers, dNTPs, etc.

Question 16

Non-nucleotide linkers

Answer 16

added density, slows down the DNA
HEO (hexaethyleneoxide)
shifts 2.5 base pairs
helps with overlapping alleles without chaining the primers

Question 17

Amelogenin

Answer 17

gene for protein in tooth enamel
found on sex chromosomes
6 base pair deletion on X chromosome
combine with STRs for sex determination