GENETICS Flashcards
Detects fetal Down Syndrome and other autosomal trisomies
Aneuploidy screening
Clinically useful if the fetus is at risk for an X-linked disorder
Fetal sex determination
May also be beneficial if the fetus is at risk for congenital adrenal hyperplasia because maternal corticosteroid therapy may be avoided if the fetus is male
Fetal sex determination
Fetal cells are present in maternal blood at a _______ concentration
very low
released from apopotic placental triphoblast—rather than actual fetal cells—and can be reliably detected in maternal blood after 7 weeks’ gestation
Cell free fetal DNA
If a specific disease causing gene has not been identified, then _________ may be used to estimate the likelihood that an individual or fetus has inherited the abnormal trait
linkage analysis
Uses the principles of PCR (polymerase chain reaction) and nucleic acid hybridization to screen DNA
Chromosomal Microarray Analysis
For prenatal diagnosis for stillbirth evaluation
Chromosomal Microarray analysis
allows identification of one or several DNA fragments of interest
Southern blotting
Enables the rapid synthesis of large amounts of a specific DNA sequence or gene
PCR
For any tissue containing dividing cells or cells that can be stimulated to divide
Cytogenic analysis
Provides a rapid method for determining numerical changes of selected chromosomes and confirming the presence or absence of a specific gene or DNA sequence
Flourescence In Situ Hybridization (FISH)
A recessive trait is expressed only when both copies of the gene function in the same way
Autosomal Recessive Inheritance
When considering inheritance, it is the ________ that is dominant or recessive, not the genotype function in the same way
phenotype
A __________ is caused by a mutation or alteration in a single locus or gene in one or both members of a gene pair
monogenic disorder
Mechanism may be either mitotic nondisjunction or parental correction of a meiotic error
Confined placental mosaicism
Likely arises from a mitotic error in cells destined to become the gonad and results in population of abnormal germ cells
Gonadal mosaicism
A mosaic individual has two or more cytogenetically distinct cell lines that are derived from a single zygote
Chromosomal mosaicism
Results when deletions occur at both ends of the same chromosome and the ends come together
Ring chromosomes
Breaks in both p and q arms
Pericentric inversion
Two breaks within one arm
Paracentric inversion
These abnormal chromosomes are composed of either two q arms or two p arms of one chromosome fused together
Isochromosomes
Can arise when the centromere breaks transversely instead of longitudinally during meiosis II or mitosis
Isochromosomes
Can also result from a meiotic error in a chromosome with a robertsonian translocation
Isochromosomes
Involves only acrocentric chromosomes which are chromosomes 13,14,15,21 and 22
Robertsonian translocation
The q arms of two acrocentric chromosomes fuse at one centromere to form a derivative chromosome
Robertsonian translocation
Develops when there are breaks in two different chromosomes and the broken fragments are exchanged, so that each affected chromosome contains a fragment of the other
Reciprocal translocation
DNA arrangements in which a segment of DNA breaks away from one chromosome and attaches to another
Chromosomal Translocations
The arranged chromosomes are called _________
derivative chromosomes
2 types of derivative chromosomes are:
Reciprocal
Robertsonian
Examples of Microduplication syndrome:
- Velocardiofacial/DiGeorge
- Smith-Magenis
- Williams-Beuren
Microdeletion syndrome are also known as:
DiGeorge Syndrome
Sphrintzen syndrome
Velocardiofacial syndrome
45,X
Turner Syndrome (Monosomy X)
47,XXY
Klinefelter Syndrome
A lethal aneuploidy, more than 90% of fetuses with either a dandric or digynic form have multiple structural anomalies (CNS, heart, face and extremities, severe growth restriction)
Triploidy
Extra chromosomal set is maternal, and the egg fails to undergo the first or second meiotic division before fertilization
Digynic triploidy (type II triploidy)
Extra chromosomal set is paternal resulting from fertilization of one egg by two sperm or by a single diploid
Diandic triploidy (type I triploidy)
Account for approximately 20% of spontaneous abortions
Polyploidy
Abnormal number of complete haploid chromosomal sets
Polyploidy
_________ is the most common trisomy found in the first-trimester losses
Trisomy 16
