🧬 DNA, Chromosomes & Forensics – Study Guide (copy)
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38 Terms
Chromosome
A tightly coiled structure of DNA and proteins that carries genetic information.
Number of human chromosomes
Humans have 46 chromosomes (23 pairs).
Karyotype
A picture showing all chromosomes arranged in pairs.
Normal human karyotype
46 chromosomes total.
Male karyotype
XY.
Female karyotype
XX.
Monomer of DNA
Nucleotide.
Nucleotide components
Phosphate group, deoxyribose sugar, nitrogenous base.
Adenine (A)
Pairs with Thymine (T).
Thymine (T)
Pairs with Adenine (A).
Cytosine (C)
Pairs with Guanine (G).
Guanine (G)
Pairs with Cytosine (C).
DNA structure
Double helix.
DNA strands
Two strands.
Complementary bases
A–T and C–G.
Hydrogen bonds
Hold base pairs together.
Sugar-phosphate backbone
The sides of the DNA ladder.
Antiparallel strands
DNA strands run in opposite directions (5′→3′ and 3′→5′).
Purpose of DNA replication
To copy DNA so each new cell gets identical genetic information.
Helicase
Unzips DNA by breaking hydrogen bonds.
Primase
Adds RNA primers to start replication.
DNA polymerase
Builds new DNA by adding complementary nucleotides and proofreading.
DNA ligase
Connects DNA fragments together.
Leading strand
Made continuously toward the replication fork.
Lagging strand
Made in short pieces called Okazaki fragments.
Semi-conservative replication
Each new DNA molecule has one original strand and one new strand.
Template strand
Original DNA strand used for copying.
Complementary strand
New strand built to match the template.
Roy Brown case
A man wrongfully convicted of rape in the 1990s.
What freed Roy Brown
DNA testing proved his innocence.
Purpose of DNA profiling
To identify individuals based on unique DNA patterns.
STRs (Short Tandem Repeats)
Short repeating sections of DNA.
Why use STRs
They vary the most between people and are easier to measure than the entire genome.
How to compare DNA
Match banding patterns between samples — same pattern = same person.
CODIS (Combined DNA Index System)
National FBI DNA database.
Number of STRs used
20 standard STR locations.
Odds of two people matching
Less than 1 in a billion (except identical twins).
Roy Brown Case Outcome
Proved DNA profiling is far more accurate than older forensic methods.
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