Chromosomes
Karotypes are used to
1) Can confirm a clinical diagnosis 2) Can reveal effects of environmental toxins 3) Can clarify evolutionary relationships
A karyotype can be abnormal in what two way?
1) In chromosome number 2) In chromosome structure
Triploid is produced in what two ways?
1. fertilization of one egg by two sperm 2. fusion of haploid and diploid gametes
Which chromosomes of trisomes are seen in newborns?
21, 18, and 13
Humans have how many chromosome types?
23; autosomes numbered 1-22 and sex chromosomes: X and Y
Abnormal chromosomes account for at least how many spontaneous abortions?
50%
Karyotype
A chromosome chart Displays chromosomes arranged by size and structure
Fetal Cell Sorting
A new technique detects fetal mRNA in the bloodstream of the mother
Ideogram
A schematic chromosome map Indicates chromosome arms (p or q) and delineates major regions and subregions by numbers
XYY Syndrome
Also known as Jacobs syndrome 1 in 1,000 male births 96% are phenotypically normal Modest phenotypes may include great height, acne, speech and reading disabilities Studies suggesting increase in aggressive behaviors are not supported
mosaic
An individual with two chromosomally-distinct cell populations
Metacentric
At midpoint
Telocentric
At tip
Turner Syndrome
Called the XO syndrome 1 in 2,500 female births 99% of affected fetuses die in utero Features include short stature, webbing at back of neck, incomplete sexual development (infertile), impaired hearing Individuals who are mosaics may have children
Triplo-X
Called the XXX syndrome 1 in 1,000 female births Few modest effects on phenotype include tallness, menstrual irregularities and slight impact on intelligence X-inactivation of two X chromosomes occurs and cells have two Barr bodies May compensate for presence of extra X
Klinefelter Syndrome
Called the XXY syndrome 1 in 500 male births Phenotypes include: - Incomplete sexual development - Rudimentary testes and prostate - Long limbs, large hands and feet - Some breast tissue development Most common cause of male infertility
Acrocentric
Close to end
A chromosome consists primarily of ___ and ___
DNA; protein
What are genes associated with down syndrome?
DYRK1A, DSCR1, and NFATc
Amniocentesis
Detects about 1,000 of the more than 5,000 known chromosomal and biochemical problems
What is an example of Trisomy 21?
Down syndrome
What is trisomy 18 known as?
Edwards syndrome
FISH
Fluorescence in situ hybridization DNA probes labeled with fluorescing dye bind complementary DNA used to determine down syndrome
Submetacentric
Off-center
What is trisomy 13 known as?
Patau syndrome
Chorionic Villi Sampling
Performed during 10-12th week of pregnancy Provides earlier results than amniocentesis However, it does not detect metabolic problems - And has greater risk of spontaneous abortion
Nondisjunction
The failure of chromosomes to separate normally during meiosis Produces gamete with an extra chromosome and another with one missing chromosome
Centromeres
The largest constriction of the chromosome and where spindle fibers attach
ring chromosome
a chromosome that forms a ring due to deletions in telomeres, which cause ends to adhere
isochromosome
a chromosome with identical arms
NFATc
a transcription factor that affects expression of genes important in central nervous system development regulated by levelsof DYRK1A and DSCR1
DSCR1
alters synapses
aneuploidy
an extra or missing chromosome
What happens when nondisjunction occurs in Meiosis II?
both sister chromatids are in one gamete
triploid
cells have three sets of chromosomes
Telomeres
chromosome tips composed of many repeats of TTAGGG - Shorten with each cell division
What happens when nondisjunction occurs during Meiosis 1?
copies of both homologs are in one gamete
Heterochromatin
darkly staining - Consists mostly of repetitive DNA
Describe Edwards syndrome
due to nondisjunction in meiosis II in oocyte and do not survive
A mitotic nondisjunction event that occurs ______ can have serious effects on the health of the individual
early in development
Most autosomal aneuploids cease developing as ____ or ___
embryos; fetuses
Centromeres are replicated when?
end of S-phase
DYRK1A
expressed in brain(hippocampus, cortex, and cerebellum) and heart starts amyloid formation
polyploidy
extra chromosomes sets
T/F Excess genetic material has less effects on health than a deficit.
false, it has milder effects
How are fetal cells distinguished from maternal cells?
fluorescense-activated cell sorter and identifies cell-surface markers
What happens when aneuploidy occurs during mitosis?
groups of somatic cells are produced with extra or missing chromosomes
Describe Patau syndrome
it is very rare and generally do not survive 6 months serious mental and physicial disabilites distinctive feature is eye fusion
Euchromatin
lighter-staining - Contains most protein-encoding genes
describe down syndrome
most common trisomy among newborns they have distinctive facial and physical problems they have varying degrees of developmental disabilites individuals are more likely to develop leukemia it is linked to one form of Alzheimer disease
monosomy
one chromosome absent
trisomy
one chromosome extra
deletion
part of a chromosome missing
duplication
part of a chromosome present twice
the bases that form the centromere are_____
repeats of a 171-base DNA sequence
inversion
segment of chromosome reversed
What are the characteristics of Edwards syndrome?
serious mental and physical disabilites distinctive feature: oddly-clenched fists
How are chromosomes distinguished?
size and shape
Cytogenetics
subdiscipline within genetics Deals with chromosome variations
what are the essential parts of chromosome?
telomeres, origins of replication sites ( ORIs), and centromere
those who are born with aneuploidy either have ____ or ____
trisomy; monosomy
T/F most large-scale chromosomal abnormalities present in all cells disrupt or halt prenatal development
true
translocation
two chromosomes join long arms or exchange parts
What tool is used to perform amniocentesis?
ultrasound