8.22.16 Lecture Flashcards
What is clinical cytogenetics?
The study of abnormalities of chromosome number and structure in relation to human disease
True or false - cytogenetic abnormalities are collectively more common than all Mendelian single gene disorders.
True
Cytogenetic abnormalities account for ___ live births.
1/154
The incidence of cytogenetic abnormalities in children of mothers >35 years old is ___.
1/50
What are the 6 major indications for cytogenetic analysis?
- Problems with early childhood growth and development (failure to thrive, abnormal physical appearance and/or internal structural abnormalities, mental retardation, ambiguous genitalia)
- Stillbirths and neonatal deaths that have the appearance of a cytogenetic abnormality
- History of infertility or recurrent miscarriage
- Known or suspected chromosome abnormality in a first degree relative
- Maternal age >35
- Cancer
What are the common types of dividing nucleated cells or tissues used for cytogenetic analysis?
- White blood cells (T lymphocytes) from peripheral blood
- Amniotic cells
- Cell of the chorionic villi (extra-embryonic fetal tissue that form the surface of the chorionic sac)
- Fibroblasts
- Cancer cells
- Bone marrow
How are chromosomes classified?
By position of centromere
What are the 3 classifications of chromosomes?
- Metacentric: centromere found midway
- Submetacentric: centromere off-center, arms of equal length
- Acrocentric: centromere very near on end, produces p arm known as a satellite
What are the 5 acrocentric chromosomes in humans?
13, 14, 15, 21, 22
Acrocentric satellite arms contain many copies of genes coding for ___.
rRNA
___ created by various staining procedures are unique to each chromosome.
Banding patterns
Which chromosome arm is longer? Which is shorter?
q; p
How are chromosomes numbered?
Example: 1p12 = chromosome 1, p arm, region 1, band 2 - note that regions are numbered from the centromere to the telomere
Normally, staining occurs during ___. However, higher resolutions are obtained when chromosomes are less condensed and are in ___.
Metaphase; prophase or prometaphase
What are the properties of dark bands stained with Giemsa?
- Stains strongly with quinicrine
- Maybe AT-rich
- Early condensation, late replication
- Gene poor
- Alu poor, LINE rich
What are the properties of pale bands stained with Giemsa?
- Stains weakly with quinicrine
- Maybe CG-rich
- Late condensation, early replication
- Gene rich
- LINE poor, Alu rich
What are several alternative chromosome staining methods?
- Q-banding (uses quinicrine, correlates to G-bands)
- R-banding (reverse Giemsa pattern)
- Fluorescence R-banding (fluorescent bands correlate to light bands in Giemsa)
- Prometaphase banding (higher resolution, G or R-banding)
What do the following abbreviations stand for regarding the description of chromosomal abnormalities?
- ,
- -
- ( )
- +
- ;
- del
- der
- dic
- dup
- fra
- i
- ins
- inv
- .ish
- mar
- mat
- p
- pat
- q
- r
- rob
- t
- ter
- separates chromosome number, sex chromosome, chromosomal abnormalities
- loss of chromosome
- surround structurally altered chromosomes/break points
- gain of chromosome
- separates rearranged chromosomes and breakpoints involve more than one chromosome
- deletion
- derivative chromosome (translation chromosome derived from 1 chromosome and containing its centromere)
- dicentric chromsome
- duplication of a portion
- fragile site
- isochromosome (arms are the same)
- insertion
- inversion
- precedes karyotype results from FISH
- marker chromosome (unidentifiable piece)
- maternally derived chromosome rearrangement
- short arm
- paternally derived chromosome rearrangement
- long arm
- ring chromosome
- Robertsonian translocation
- translocation
- terminal end of arm
What are aneuploidies?
Abnormalities of chromosome number; most common type of human chromosome disorder
What is the frequency of aneuploidies in all pregnancies?
5%
___ are incompatible with live births.
Autosomal monosomies