2.1 test

Question 1

Types of genetic tests

Answer 1

Carrier screening (for heterozygotes of recessive diseases)
PGD (preimplantation genetic diagnosis - used with IVF)
Fetal screening (includes amniocentesis, chorionic villi sampling, and ultrasound)
Newborn screening (routine tests shortly after baby is born)

Question 2

PGD

Answer 2

Preimplantation genetic diagnosis - must be used with IVF to determine a genetic condition before an embryo is implanted in the uterus

Single cell is removed from an embryo and examined; parents/doctors can choose which embryo to implant

Egg + sperm combine to form a blastocyst, whose DNA/chromosomes are then examined

Question 3

Amniocentesis

Answer 3

• Weeks 14-20
• Needle inserted through abdomen to uterus
• Sample is of amniotic fluid (liquid that cushions and surrounds the amniotic sac), which contains fetal cells
• Can detect neural tube defects

Question 4

CVS

Answer 4

• Weeks 10-12
• 2 options- catheter through cervix or needle through abdomen
• Sample is from chorionic villus cells (from the placenta, whose DNA is the same as the fetus’ DNA)
• Cannot detect neural tube defects

Question 5

Ultrasound

Answer 5

• Can image non-hollow organs like gallbladder, liver, pancreas, etc.
• Cannot image lungs (too much air for ultrasound waves to be transmitted), and waves also cannot pass through bone
• Can image liquid around bones or air-filled organs but not the actual structures

Question 6

Newborn screening

Answer 6

Screen for 4-30 genetic/metabolic disorders when the baby is 1-2 days old

Question 7

Cystic Fibrosis

Answer 7

Autosomal recessive
Treatment- antibiotics and mucus-thinning drugs

Question 8

Huntington’s

Answer 8

Autosomal dominant
Neuron degeneration, leading to mental decline
Treatment- PT, drugs to help with chorea (haloperidol, tetrabenazine, etc.)

Question 9

Duchenne Muscular Dystrophy

Answer 9

X-linked recessive trait
Dystrophin gene is mutated -> progressive muscle degeneration and weakness

Question 10

Leber hereditary optic neuropathy

Answer 10

• Mitochondrial disorder - passed down through mother’s DNA
• Vision loss, blindness

Question 11

Alzheimer’s

Answer 11

Autosomal dominant
Multifactorial condition (mutations in multiple genes and environmental causes

Question 12

PCR temperatures

Answer 12

Denature- 94 to 96 deg. C
Anneal- 50 to 65 deg. C
Extend- 72 deg. C

Question 13

PCR steps

Answer 13

1) High temperatures break down hydrogen bonds between complementary bases in DNA, causing the 2 strands to separate
2) Primers bind to DNA to mark where Taq polymerase will add nucleotides
3) Taq polymerase attaches to the primers and works in the 3’ to 5’ direction

Question 14

Restriction enzyme digest for PTC alleles (T & t)

Answer 14

Enzyme HaeIII cuts the sequence GG | CC
GGCC is only present in the dominant PTC allele (T) -> 2 fragments per allele are produced
GCC is present in the recessive PTC allele (t) -> HaeIII does not cut -> 1 whole, uncut fragment per allele
TT- 2 bands
Tt- 3 bands
Tt- 1 band

Question 14

SNPs

Answer 14

Single-nucleotide polymorphism- a segment of DNA that has a variation in just 1 nucleotide
Can occur in a non-coding region -> no impact; but can change protein folding if it occurs in a coding region

Question 15

PTC gene

Answer 15

Inability to taste PTC is recessive
Gene for PTC taste receptor is TAS2R38 (identified in 2003)