Numerical And Structural Abnormalities Flashcards
What is euploidy?
Exact multiples of haploid chromosome set. Humans are diploid; any more is not compatible with life (triploidy or tetraploidy)
How do you get tetraploidy?
Post meiotic event; presents as a duplication of a diploid complement most likely due to a failed early mitotic cleavage
How does triploidy occur?
can be due to failure of gametogenesis of one of the mitotic divisions giving a 2N gamete that gets fertilized by another gamete
-or a 3N complement can come from dispermy
aneuploidy
gain or loss of individual chromosomes; trisomy or monosomy
What is the only viable monosomy?
Turner’s syndrome
What are the 3 live-born trisomys?
Chromosome 21: Down’s
Chromosome 13
Chromosome 18
Aneuploidies are usually a result of____
meiotic or mitotic nondysjunction
Are aneuplodies inherited?
Not usually
What are the 3 basic components of chromosomal nomenclature?
- total number of chromosomes
- sex chromosome complement
- any chromosomal abnormalities
If a meiotic error produces a gamete with 2 copies of chromosome A what will happen?
fertilization with a normal gamete will result in trisomy
Is it possible for a embryo with trisomy 21 to produce disomic cell?
Yes; it would be mosaic
What is mosaicism?
presence of at least 2 different cell lines with at least one clear variation between them
How is a mosaic different from a chimera?
mosaic individuals have fewer variations
chimeras have many variations traced back to their cell lines
Trisomy 21 characteristics include
short stature low set ears microcephaly mental retardation upslanting eyes short hands eye folds protruding tongue infertile
Trisomy 13 (Patau syndrome) characteristics
-failure to thrive
-cleft lip and palate
-rocker bottom feet
polydactyly
-punched out scalp
-small head
-heart defect
Symptoms of Trisomy 18 (Edwards syndrome)
- low birthweight
- small mouth/jaw
- ventricular septal defect
- hypoplasia of muscles
- prominent occiput
- low set malformed ears
- rocker bottom feet
- crossed fingers
- -outlook is bleak even if the infant survives the 1st year
Sex chromosome aneuploidies are frequently more mild than autosomal aneuploidies because
of X inactivation
Describe XXX female.
1/1000 births, usually due to maternal meiosis I error
- average to tall stature
- learning deficit possible
- some fertility problems possible`
Describe XYY
-1/1000 male live births
-failure of paternal meiosis
-tall stature
-normal intelligence
normal fertility
-indistinguishable from xy
-originally it was thought that these people has an increased testerone and thus increased propeensity for violence, but not true
Klinefelter syndrome
- 1/1000 male life births
- 50% due to meiosis I error in father
- tall stature
- infertility
- some female characteristics may develop
- learnign deficiency possible
Turner Syndrome
- incidence: 1/5000 live female births
- short stature
- webbed neck
- edema of the hands and feet at birth; after birth, short hands and feet
- heart and renal anomalies
- increased carrying angle of the elbow
- shield chest
- low posterior hairlline
- normal intelligence, some learning disability
- usually infertile
How does Turner Syndrome arise?
about half have 45, X karyotype
- 15% have deletion or rearrangement on X
- 10% more are mosaics 45X/46, XX; or 45X, 46 XY
Males that have the mosaic male female Turner syndrome pattern are usually ok. Why aren’t the girls?
They are at increased with of gonadoblastoma–> gonad removal recommended
What are the major issues of Turner syndrome?
growth hormone to prevent short stature
- monitor for heart malfuncitons
- karyotype to be sure no Y chromosome is present
- counseling for probable infertility
