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What is cytogenetics?
The study of diseases related to chromosomal abnormalities
What is the leading cause of pregnancy miscarriage?
In what stage are chromosomes viewed for cytokenetic studies?
Metaphase - Mitosis
What is the difference b/t metacentric, submetacentric and acrocentric chromosomes?
- Metacentric: centromere at center
- Submetacentric: centromere farther from center
- Acrocentric: centromere closer to telomere near end where p-arm is really short
What are the four values of utilizing FISH?
- 1) microdeletions
- 2) gene amplification
- 3) abnormal karyotype detection
- 4) cancer studies
What is Polyploidy?
Gain of one or more chromosome sets
What is aneuploidy and what are two results of it?
- Aneuploidy: gain or loss of one chromosome
- Result: trisomy or monosomy
What causes aneuploidy?
Dysjunction at Meiosis I or II
Are monosomies lethal or viable?
What are the three viable trisomy chromosomes?
13, 18, 21
What is the disease related to Trisomy 21 and what are its symptoms (3)?
- Disease: Down Syndrome
- Symptoms: distinct face, GI problems, Heart defects
At what age does the incidence of Trisomy 21 increase?
>35 (although more incidences happen at younger ages just because more babies are born at this time)
What is the disease associated with Trisomy 18 and what are its symptoms (6)?
- Disease: Edward Syndrome
- Symptoms: low weight, mental retardation, clenched fist, overlapping fingers, small eyes, omphlaocele (gut opened)
What is the disease associated with Trisomy 13 and what are its symptoms (3)?
- Disease: Patau Syndrome
- Syndrome: cleft palate, postaxial polydactyly, large, triangular nose
What type of disease is Turner syndrome and what are its symptoms (2)?
- Monosomy, 45 XO
- symptoms: webbed neck, short stature
What is klinefelter syndrome and what are its symptoms (4)?
- Trisomy, 47 XXY
- Symptoms: tall, sterile, gynecomastia, small testes
Why is the SRY gene important?
It is what makes a male a true male. It is found on the Y chromosome
How does an XX male form?
The SRY gene is crossed during synapse of the pseudoautosomal region onto the X chromosome
How does and XY Female form?
The SRY gene is crossed over to the X chromosome and the Y is passed on to the female
What is translocation?
exchange of genetic material between non-homologous chromosomes
How does a reciprocal translocation occur?
Two parts of two chromosomes break and fuse with the other chromosome (3 with 6 and 6 with 3)
What are the percentages of offspring when a reciprocal translocation occurs?
- 25% normal
- 25% gen. abnormal, phen. normal
- 50% gen/pen abnormal
What is unique about a Robertsonian translocation compared to a reciprocal?
Robertsonian:Only on acrocentric chromosomes (centromere by telomere at small p-arm)
What is the karyotype count for a Roberstonian trans.?
45, b/c they lose two short arms and gain one long arm
What is the chance of a robertsonian mother bearing a down syndrome child?
What are the three types of chromosomal deletions (TIR)?
- 1) Terminal
- 2) Interstitial
- 3) Ring
What is a terminal deletion ?
single break and loss of one end of the chromosome
What is an interstitial deletion?
break at two places in an arm and fusion of the blunt ends
What is a ring deletion?
Two broken tips that cause the chromosome to fuse in ring form
What are the two types of inversions?
- 1) Pericentric: involving the centromere2) Paracentric: not involving the centromere***when they come together the cut pieces flip before inserting
What is PKU?
- Autosomal recessive disease
- Lack of phenylalanine hydroxylase
- phenylalanine builds up and is also converted to an acid
- these cause neuronal damage
What type of disease is Tay-Sachs and what population receives it most often?
- Autosomal recessive (HEX A)
- Ashkenazi Jews
How does Preimplantation genetic diagnosis (PGD) work?
- Have to be invitro fertilized
- one of the 8 cells removed for testing of Tay-Sachs or other heterozygote diseases
What are the four methods for prenatal screening and what part do they test?
- 1) CVS- fetal tissue
- 2) NTU- maternal blood/visual
- 3) Amniocentesis- amniotic fluid
- 4) ultrasound - visual
What does a high AFP and a low AFP tell about a fetus?
- High: risk for Neural Tube defect (NTD)
- Low: risk for trisomy
What two prenatal tests can be used for NTD and Trisomy?
NTU and Amniocentesis
At what weeks should the four tests be performed?
- 1) CVS 9-12 wks
- 2) NTU 11-14 wks
- 3) Amniocentesis 15-17 wks
- 4) anytime
When should a triple screen be performed?
What is extra in a quadruple test?
inhibin-A (to help measure down syndrome)
What are the three main enzymes tested in triple/quadruple test?