PLTW MI Unit TWO

Maternal Serum Screening — First Trimester (hCG & PAPP-A)

Non-invasive blood test at 10-14 weeks measuring hCG and PAPP-A; estimates risk for Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13).

Maternal Serum Screening — Second Trimester / Quad Screen (AFP, hCG, DIA, uE3)

Blood test at 15-20 weeks measuring AFP, hCG, DIA, and uE3; screens for Down syndrome, Trisomy 18, and neural tube defects like spina bifida.

Nuchal Translucency (NT) Ultrasound

First-trimester screening combining blood test (hCG + PAPP-A) with measurement of nuchal translucency; screens for Trisomy 21 and Trisomy 18.

Anatomy Ultrasound

Standard ultrasound checking fetal appearance, growth, and structural development; identifies visible physical birth defects.

Noninvasive Prenatal Screening (NIPS / Cell-Free Fetal DNA)

Blood test from 10+ weeks analyzing fetal DNA fragments; highly accurate screening for Trisomy 21, 18, 13, and sex-chromosome disorders.

Chorionic Villus Sampling (CVS)

Diagnostic test at 10-12 weeks collecting placental tissue; diagnoses chromosomal abnormalities like Trisomy 21, 18, 13, and some inherited conditions.

Amniocentesis

Diagnostic test at 15-20 weeks removing amniotic fluid; diagnoses chromosomal disorders, genetic diseases, and certain infections.

Importance of Genetic Counseling

Helps parents understand inheritance, genetic risks, test options, and results to make informed medical decisions before and during pregnancy.

Karyotype

Visual arrangement of chromosomes; used to check chromosome count (should be 46), sex chromosomes (XX/XY), and abnormalities such as extra or missing chromosomes.

Autosomal Chromosomes

Chromosomes 1-22 that do not determine sex.

Sex Chromosomes

X and Y chromosomes; determine biological sex.

Female Karyotype

Has 46 chromosomes including two X chromosomes (XX).

Male Karyotype

Has 46 chromosomes including one X and one Y chromosome (XY).

Trisomy 21 (Down Syndrome)

Caused by three copies of chromosome 21; leads to developmental delays, characteristic facial features, and varying health concerns.

Trisomy 18 (Edwards Syndrome)

Caused by three copies of chromosome 18; associated with severe developmental delays, organ defects, and life-threatening complications.

Trisomy 13 (Patau Syndrome)

Caused by three copies of chromosome 13; associated with severe developmental abnormalities, including brain, heart, and facial defects.

Purpose of PCR

To make millions of copies of a specific DNA segment for testing, analysis, or identification.

Denaturation

First Step of PCR; DNA is heated to 90-98°C to separate the two strands.

Annealing

Second Step of PCR; Temperature drops to 40-60°C so primers can bind to the target sequence.

Extension

Last Step of PCR; Temperature rises to 70-75°C; Taq polymerase builds new DNA strands using dNTPs.

Thermal Cycler

The machine used to run PCR by changing the temperature automatically.

Primer

Short sequence of DNA that marks where DNA synthesis should start during PCR.

dNTPs

Nucleotide building blocks used to create new DNA during PCR.

Taq Polymerase

Heat-resistant enzyme that synthesizes DNA during PCR.

SNP

aka (Single Nucleotide Polymorphism); a variation at a single nucleotide position in DNA that can affect traits or indicate genetic differences.

Purpose of Gel Electrophoresis

To separate DNA fragments by size so researchers can determine genotype, identify SNP patterns, compare DNA samples, or confirm PCR results; essential for visualizing differences in DNA length caused by mutations or restriction sites.

Direction DNA Moves in Gel Electrophoresis

DNA moves toward the positive end (anode) because DNA is negatively charged.

Short vs Long DNA Fragments

Shorter fragments travel more easily through the gel pores, so they migrate farther than longer fragments.

What Band Number Represents

The number of bands reflects genotype: one band = homozygous, two bands = heterozygous (two fragment sizes).

How to Read Gel Electrophoresis

Compare sample band patterns to known controls; shorter fragments migrate farther, longer fragments remain closer to wells; analyze number and position of bands to determine genotype.

TT (homozygous taster)

2 bands on gel electrophoresis (both alleles cut by restriction enzyme)

tt (homozygous non-taster)

1 band on gel electrophoresis (no restriction enzyme cut)

Tt (heterozygous)

3 bands on gel electrophoresis (one allele cut, one uncut)

PGT (Preimplantation genetic testing)

screening technique performed on embryos created during IVF that screens for extra or missing chromosomes, single-gene disorders, structural rearrangements, and healthy embryos are selected for transfer

IVF (In vitro fertilization)

medical procedure that involves retrieving eggs from an ovary and is fertilized with sperm in a laboratory which reduces the risk of genetic/chromosomal risks by bypassing natural fertilization and only selected eggs that are healthy

Gene therapy

The addition/replacement of a gene (without changing it) of a person carrying a genetic disease and/or disorder

Gene editing

The actual technique that uses tools that cut and replace DNA and replace mutated genes using gene editing techniques.

Vectors

A genetic agent that carries modified genetic material and can be used to introduce extra genes into the genome of an organism.

Plasmid

a vector that can carry DNA of any gene size, is unlikely to cause an immune response, however is less efficient, does not integrate, and Cells may or may not uptake plasmid DNA.

Liposome

carries DNA of any size without cell specificity, unlikely immune response, no integration, and less efficient uptake by cells

Herpes Virus

also a vector that can carry Carry up to 20k base pairs, is likely to cause an immune response, however is is less efficient, does not integrate, and only infects nervous system cells

Adeno-associated virus

carries up to 5 kb DNA into dividing/non-dividing cells of various types, unlikely immune response, integrates, and more efficient

Adenovirus

carries up to 7.5 kb DNA into dividing/non-dividing cells variably, likely immune response, no integration, and highly efficient

Retrovirus

carries up to 8 kb RNA only into dividing cells, likely immune response, integrates randomly with cancer risk, and less efficient

Lentivirus

carries up to 8 kb RNA into dividing/non-dividing cells variably, unlikely immune response, integrates randomly with cancer risk, and more efficient

in vivo

Using a viral vector to carry an altered therapeutic gene directly into the patient's body.

ex vivo

Extracting cells from the body, genetically altered in a lab, and transplanting them back into the body.

CRISPR-Cas9

The actual gene-editing tool, derived from the bacterial defense system (CRISPR) that acts as "molecular scissors" (Cas9) to cut and modify existing DNA.

CRISPR

A set of DNA sequences stored inside bacteria that store snippets of viral DNA, allowing bacteria to recognize and fight off future infections/viruses.

Cas9

The enzyme that guides RNA acting as molecular scissors that's capable of cutting both strands of DNA.

Insert

A functional gene, when given to the patient, gives their body the ability to produce a functional protein.

Disable

dysfunctional gene is disabled, which eliminates impact of protein

Repair

dysfunctional gene is disabled, to produce a functional protein