Topic 14.2: Chromosomal abnormalities Flashcards
what are the two types of chromosomal abnormalities
numerical and structural
what are the two types of chromosomal abnormalities considering their consequences
balanced and unbalanced
what is balanced abnormalities
no genetic information lost and/or no phenotypic changes
what is unbalanced abnormalities
anything that is not balanced
what are some numerical abnormalities
POLYPLOIDY
gain of extra haploid set of chromosomes (23)
eg: triploidy - 3n=69
most commonly caused by polyspermy - two sperm fertilize one egg
occurs in pregnancies and causes around 15% of miscarriages
ANEUPLOIDY
loss or gain of whole chromosome
this is trisomies and monosomies
caused by meiotic non disjunction
MOSAICISM
presence of two or more cell lines in an individual
throughout the body or tissue specific
caused by mitotic non disjunction
what are examples of triosomies that are viable for life
downs syndrome 47(+21)
patau syndrome 47 (+13)
edwards syndrome 47 (+18)
klinefelter syndrome 47 (XXY)` (males)
what are examples of monosomies that are viable for life
turner syndrome 45, X (females)
what are the types of structural abnormalities
deletion or microdeletions- of a whole part of a chromosome
duplication - of a whole part of a chromosome
inversion - part of chromosome swapped. either paracentric - not involve centromere or pericentric - over the centromere
substitution/insertion - one part of one chromosome inserted into another
translocation - two chromosomes swap information, either reciprocal or robertsonian
isochromosomes - one chromosome has two p arms and the other of the same pair has two q arms
ring chromosomes - can fuse to form a ring
marker chromosome - extra bit of DNA on top of 46 chromosome, genes on them can cause disease
what are the two types of translocation
reciprocal or roberstonian
what is reciprocal translocation
where a bit of chromosome swaps from one chromosome to another
- can be balanced (all info is there) or unbalanced (causes disease)
instead of forming two bivalents during meiosis, forms quadrivalent (sequence similarities combine), which when segregated will have 3 possible ways, 6 gametes (alternate, homologous, non homologous) and will result in a 3:1 non disjunction (unbalanced:balanced). balanced = alternate, contains all the correct amount of information
what is the karyotype of a normal male
46, XY
what is the karyotype of a normal female
46, XX
what is robertsonian translocation
2 acrocentric chromosomes fuse (small p arm)
q arms fuse and become one chromosome and p arms lost
results in 45 chromosomes in balanced carriers
females higher risk than males
problem during meiosis not mitosis
trivalent will form during meiosis, segregation with 6 possible outcomes
when mixed with normal chromosomes from other gamete (sex cell) = aneuploidy risk
what can robertsonian translocation cause
downs syndrome as happens on chromosome 21
what does balanced mean
lost DNA but not lost genetic information as p arms contain very little information so phenotype unaffected
how can robertsonian translocation cause downs syndrome
3 copies of chromosome 21 in one of the gametes as two q arms fuse plus a copy from a normal chromosome
what is cytogenetic testing
analysis = karyotyping flourescent in situ hybridisation microarray hybridisation DNA sequencing and others
why do we perform cytogenetic testing
- diagnosis and prognosis of clinical problems - syndrome, account for pregnancy loss
- better clinical management - hormone treatment
- access future reproductive risks - downs
- prenatal diagnosis
why would someone want cytogenetic testing
prenatal diagnosis birth defects abnormal sexual development infertility recurrent fetal loss leukemia solid tumors prognostic information
what does chromsomal inversion cause
Inversion does not cause the loss of genetic information. It simply rearranges the gene order or the gene sequence. There are two types of inversions namely paracentric and pericentric inversions. A paracentric inversion occurs in one arm of the chromosome without involving the centromere. Both arms of the chromosome break including the centromere during the pericentric inversion.
Non invase prenatal testing tests for
downs
fetal sex
single gene disroders
what does wild type allele mean
normal
how are mRNA missense detected
NMD
what would happen if premature stop codon in mRNA
protein degraded rather than shorter
