Bioc L06 and L07 Cytogenetics Flashcards

Question

What cancers can result from reciprocal translocation?

Answer 1

**Chronic myelogenous Leukemia (CML)****:** translocation results in fusion protein w/ tyrosine kinase activity **Burkitt Lymphoma (solid tumor)**: c-myc oncogene (on chromosome 8) placed near Ig heavy chain locus activates Ig heavy chain gene which activates c-myc

Answer 2

Translocation of **acrocentric autosomal chromosomes (13,14,15,21,22)**. Involves **loss of short arms** and **fusion of two long arms at the centromere.** **Individuals are normal** because short arms contain redundant DNA but they do have one less chromosome (loss of two but gained one robertsonian) Like reciprocal translocations, a carrier can produces 6 different gametes in two types through alternate segregation, and 6 possible conceptions if joined with normal gamete. **Conceptions that result in monosomy or trisomy are not compatible with life except one that results in trisomy 21** (causes 5% of down syndrome)

Answer 3

A type of chromosomal abnormality w/ loss of genetic material. **Terminal** deletions result in loss of the end of a chromosome. **Interstitial** deletions involve two breaks with loss of genetic material between the breaks. 1. **cri‐du‐chat syndrome** (“cry of the cat” in French) is caused by a deletion of the distal p arm of chromosome 5; the karyotype is 46, XY, del (5p). 2. **Wolf‐Hirschhorn syndrome** is caused by a deletion of the distal p arm of chromosome 4, 46, XX, del (4p). **Ring chromosomes** result from breakage on both ends of a chromosome that then fuse. May arise following genetic damage or spontaneously during development. Results in monosomy of all daughter cells.

Answer 4

Small deletions that can be terminal or interstitial, usually affecting a large number of genes leading to microdeletion syndromes (aka contiguous gene syndrome). Famous examples include: Prader‐Willi (15q11‐13) Angelman(15q11‐13) DiGeorge (22q11.2)

Answer 5

A type of chromosomal abnormality where two breaks occur and the sequence in between is reinserted inverted. If the inversion includes the centromere it is called a **pericentric inversion** Inversions that do not include the centromere are called **paracentric** inversions. The arrangements are **balanced** **so the parent is unaffected** but their inverted chromosomes can't align properly during meiosis 1 resulting in **offspring with deletions or insertions**

Answer 6

"The search in a population for persons possessing certain genotypes that (1) are already associated with disease or predisposition to disease or (2) may lead to disease in their descendants" The three types are: 1. Population screening (includes newborn) 2. Prenatal screening 3. Family screening

Answer 7

PKU, galactosemia and hypothyroidism

Answer 8

Autosomal recessive disease affecting metabolism 1/40 northern Europeans are carriers. MCADD newborn screening is now required. MCADD results in incomplete B-oxidation of fatty acids. Medium‐chain fatty acyl‐CoA can't be broken down to Acetyl Coa, NADH or FADH2 resulting in decreased ATP, decreased ketogenesis, faster glycogen depletion and ultimately **Hypoketotic hypoglycemia**. Treated with high carb diet and avoiding prolonged fast

Answer 9

Heterozygote screening is used to detect unaffected carriers of disease causing agents w/in populations at risk for autosomal recessive disorders. Used where prenatal diagnosis is available. **Tay-sachs** screening is common w/ the **Ashkenazi Jew** population (1/30 are carriers). Some couples avoid birth of affected child by **preimplantation genetic diagnosis (PGD)**

Answer 10

**Analysis of fetal tissue** (amniocentesis, CVS, cordocentesis, in‐vitro fertilization diagnosis) **Visualization of the fetus** (ultrasonography)

Answer 11

9-12 weeks LMP to collect fetal trophoblastic tissue for cytogenetic and DNA testing. Can detect chromosomal abnormalities and genotype

Answer 12

They are used from 11-14 weeks LMP to check for neural tube defects or and risk of trisomies. **nuchal fold measurement** (ultrasound) can detect neural tube defects * *MSAFP** (maternal serum AFP): * *High MSAFP = risk of neural tube defects**, * *Low MSAFP levels = trisomies risk**

Answer 13

Amniocentesis is used 15-17 weeks LMP. It is the collection of amniocytes and amniotic fluid for **Cytogenetic analysis, DNA testing** and **Fetal AFP** * *High fetal AFP = high NTD risk** * *Low fetal AFP levels = trisomies risk**

Answer 14

**Triple screen:** MSAFP, hCG, Estriol Many false positives with triple screen. **Quadruple Screen:** triple screen + Inhibin A (produced by placenta and ovaries, higher levels if fetus has down syndrome) A quadruple screen increases the accuracy of down syndrome screening.