Exam #5: Chromosomal Aberrations Flashcards Preview

Biochemistry > Exam #5: Chromosomal Aberrations > Flashcards

Flashcards in Exam #5: Chromosomal Aberrations Deck (25)
Loading flashcards...
1
Q

Frequency of Chromosomal Aberrations

A

The majority of fetuses w/ chromosomal aberrations are spontaneously aborted i.e. chromosomal aberrations are much more frequent at conception than at birth

For 10,000 pregnancies:

  • 800 w/ chromosomal aberrations, BUT only 50 live births
  • 47, XXY, XXX, & XYY, and then Trisomy 21 had the most live births of the numerical aberrations (15 & 10)
  • Balanced rearrangement has more live births than those two numerical aberrations
  • Unbalanced rearrangements were spontaneously aborted 85% of the time
2
Q

Two Sources of Mutation Affecting Chromosomes

A

1) Numerical Aberrations = Nondisjunction during meiosis

2) Structural Chromosomal Alterations = rearrangements, loss, & duplication of parts of a chromosome

3
Q

Balanced Alteration

A
  • Move a fragment of DNA from one chromosome to another i.e. Translocations & Insertions (Inversion too)
  • No loss or gain of genetic material
4
Q

Unbalanced Alteration

A
  • Deletions & Duplications
  • BOTH change the amount of DNA in the cell
  • BOTH have an impact on the carrier
  • Deletions are typically more severe
5
Q

Cri-Du-Chat Syndrome

A
  • Caused by a deletion on chromosome 5 (del5p)
  • Face symptoms: Microcephaly, Hypertelorism, Micrognathia
  • Brain/CNS: Severe mental retardation
  • Cardiovascular: Heart Defects
  • Other: “Cat-like cry”
6
Q

Di George Syndrome

A
  • Caused by a microdeletion on chromosome 22
  • Autosomal dominant inheritance
  • Symptoms: heart defects, immunodeficiency, hypoparathyoridism, mental retardation, cleft palate
7
Q

Why do balanced chromosomal alterations cause infertility in otherwise healthy carriers?

A
  • Unbalanced alterations affect the carrier b/c the gene dosage is changed
  • Balanced typically DO NOT
  • However, balanced alterations greatly reduce the success of meiosis & subsequent pregnancy
8
Q

Philadelphia Chromosome

A
  • Translocation between chromosomes 9 & 22
  • Moves ABL tyrosine kinase gene from chromosome 9 next to the BCR region of chromosome 22
  • BCR/ABL chimeric protein is the dominant oncogene in CML
9
Q

Robertsonian Translocation

A
  • Long & short arms of a chromosome are exchanged
  • Result is one chromosome w/ both long arms & one chromosome w/ both short arms
  • Most common with chromosomes 13 & 14 in humans
10
Q

CML

A
  • Chronic Myelogenous Leukemia

- BCR/ABL protein from translocation of chromosome 9 & 22

11
Q

Inversion

A
  • Chromosome suffers two breaks
  • Broken-off fragment is reinserted in the wrong orientation/ upside-down
  • Balanced alteration
  • Often asymptomatic in carrier BUT problems arise in offspring
12
Q

Karyotype

A
  • Studying the chromosome composition under light microscopy
  • From cultured living cells of the patient that are arrested in metaphase
13
Q

Turner Syndrome Karyotype

A
  • Monosomy of X (45,X)

- Patient is female

14
Q

Klinefelter Karyotype

A
  • 47, XXY

- Patient is male

15
Q

Down Syndrome Karyotype

A
  • Trisomy 21
16
Q

Edwards Karyotype

A
  • Trisomy 18
17
Q

Patau Karyotype

A
  • Trisomy 13
18
Q

Aneuploid

A

Uneven number of chromosomes

19
Q

What are the two sources of structural chromosomal aberrations?

A

1) Healing of ds-DNA breaks with nonhomologous end joining

2) Unbalanced recombination

20
Q

Hypertelorism

A

Increased distance between two organs, typically the eyes

21
Q

Micrognathia

A

A condition where the jaw is undersized

22
Q

Insertion

A

Moves the DNA fragment into the middle of another chromosome

23
Q

Translocation

A

Moves the DNA fragment to the end of the another chromosome

24
Q

How do you make a Karyotype?

A

1) Obtain live cell culture
2) Arrest in metaphase
3) Lyse in hypotonic solution
4) Fix to microscope slide
5) Stain

25
Q

What are the indications for a karyotype?

A
  • Problems of early growth/development
  • Stillbirth/ Neonatal death
  • Fertility problems
  • Pregnancy with advanced maternal age (>35)