Cell reproduction and the Continuity of Life: Prenatal Screening

Question 1

What is karyotyping?

Answer 1

Photographs a cell in metaphase. The picture is enlarged, and the homologous chromosomes are cut out and paired together. This is compared to a normal karyotype (White blood cell) to check for extra or missing chromosomes.

Question 2

What is an ultrasound?

Answer 2

High frequency sound waves get reflected off the fetus to create a picture. Informs on the size and position and abnormalities of the fetus. (Absent limbs, heart or bone issues, cleft palate)

Question 3

What is a fetoscopy?

Answer 3

An endoscope (tube with camera and light) is inserted into a slit in a woman’s abdomen. This directly views the fetus and makes procedures (Removing water from fetus’ brain or fetal blood transfusion) much easier. May take analytical cell samples.

Question 4

What is amniocentesis?

Answer 4

After 14 weeks, a needle is inserted into the amniotic sack, removing cell rich amniotic fluid. The cells grow in a sterile environment for karyotyping to determine chromosome number abnormalities and gender. Fluid is also checked for certain enzymes. Mostly used to detect down syndrome, which women over 40 are more likely to have. Results take several weeks.

Question 5

What is Chorionic Villus Sampling? (CVS)

Answer 5

Piece of the chorionic membrane surrounding the membrane is removed to be karyotyped, with results within one day. May be done after 9 weeks.

Question 6

What is cell-free DNA prenatal screening?

Answer 6

Noninvasive procedure that analyzes cell-free DNA fragments representing the fetus’ genetic profile. (Derived from the placenta and mother’s blood) Identifies chromosome number abnormalities. Due to being noninvasive, invasive test results may be needed to confirm positivity.

Question 7

What are the kinds of maternal blood tests?

Answer 7

• STI screening
• Antibody/Immunities against various diseases
• Blood type/rH factor
• Red blood cell counts (anemia)
• Hormones (Check above average levels of hormones, may indicate chromosome abnormalities)
• Glucose tolerance (diabetes)
• Alpha Fetoprotein test

Question 8

What is an Alpha Fetoprotein test?

Answer 8

This substance (produced by the fetus) appears in the mother’s blood at known levels. A test is taken at 15 weeks. Heightened levels indicates possible spina bifida or water in the brain, whilst lowered levels indicate down syndrome.

Question 9

What are gene specific genetic markers?

Answer 9

Used when nucleotide sequences for abnormal genes are known. A short strand of DNA (DNA probe) is made with a radioactive label and sequence that will only attach to sequences of defective genes. Becomes radioactive when attaching to a person’s DNA, being easily detectable by tests. Useful for screening carriers of sickle cell anemia.

Question 10

What disorders can be detected with DNA probes?

Answer 10

• Cystic fibrosis
• Duchenne muscular dystrophy
• Hemophilia
• Phenylketonuria
• Sickle cell anemia

Question 11

What are home pregnancy tests?

Answer 11

Devices that check urine for human chorionic gonadotropin (hcG), which is only released when pregnant. (When a fertilized egg attaches to the uterus)