Exam V: Genetics II Flashcards
Bands and Genes
Arm, region, band, sub-band
p is short arm and q is long arm
Molecular Cytogenetics
Molecular biology techniques allow more information about chromosomes to be visualized
DNA probes can be hybridized to chromosomes and cell nuclei
Fluorescent labels make probes visible
A number of techniques have been developed for different purposes
Cost more but get more information
If you can see it on a karyotype then that is cheaper, but sometimes you can’t
FISH
Fluorescent In Situ Hybridization
DNA probe from specific gene or region of chromosome
Label with fluorescent material
Hybridize to denatured DNA of chromosome spread or nucleus
Spots identify complementary sequence
FISH analysis of an interphase nucleus, using locus-specific probes
SKY
Spectral Karyotyping
Multiple dyes, probes along all chromosomes
Lots of computer analysis of data
Can have all 23 pairs of chromosomes appear different on screen
Can identify large rearrangements, such as in tumor cells
Combination of probes, metaphase spread
DNA Analysis
May look at specific genes or test for markers
Markers may be genes or repetitive DNA
Can look at gene of interest or linked markers
Choices depend on availability of tests, knowledge of gene’s identity and/or location, feasibility, cost, etc.
Use many methods applicable to other DNA studies
Linkage analysis: looking at markers associated with phenotype
RFLP Analysis
RFLP = Restriction Fragment Length Polymorphisms
Restriction enzymes digest DNA by breaking backbone only at specific DNA sequence
Sites are short and usually palindromes
Different people may have sequence differences that disrupt a restriction site
Changes the length of fragments produced by digestion with the enzyme
Palindromes: short fragments that read the same forwards as backwards
Polymorphisms interfere with restriction sites and different lengths of fragments
Factor V for example
Analysis of Factor V
Factor V Leiden is an inherited disorder of blood clotting. It is a variant of human factor V that causes a hypercoagulability disorder. Factor V Leiden is the most common hereditary hypercoagulability disorder amongst Eurasians. Dominant disorder; but displays incomplete dominance. Causes vascular thrombosis, esp DVT which can lead to pulmonary embolism.
DVTs are more likely in these individuals
Mnl 1 site is cut/fragmented
Enzyme usually cuts twice in the top orange arrows
With mutation: homozygous, just cuts once, but if heterozygous, see bands from both homozygous and normal = 4 bands of different sizes
Easy way (PCR and restriction digestion) to get diagnosis
RFLP Pedigree Analysis
RFLP anaylsis: gel with banding and pedigree to get information
Pedigree shifted to right and directly below it is the patient’s banding pattern
Not looking at actual mutation in gene, but linkage analysis
Disease that don’t know the exact mutation, but know of a mutation that is linked (extra restriction site associated with mutant gene)
Microsatellite Analysis
Microsatellites have short repeat unit, number of repeats varies considerably
Flanking DNA generally identical, use for primers
Many alleles and sensitive detection
DNA fingerprinting is another name
Variable number of repeats, and this particular region of genome, the highest number of repeats is associated with polycystic kidney disease
Flanking region is same so use same PCR primers
Largest one is associated with disorder
Down Syndrome
Trisomy 21
Mental retardation, abundant neck skin, congenital heart defects, leukemia development, epichanthic folds, single palmar crease, umbilical hernias, hypotonia, gap between first and second toe, intestinal stenosis leading to GI issues
Edward’s Syndrome
Trisomy 18
Mental retardation, low set ears, fingers overlap, heart defects, renal malformation, rocker bottom feet, short neck, prominent occiput, micrognathia (small mouth), limited hip abduction
Patau Syndrome
Trisomy 13
Microcephaly, mental retardation, polydactyly (pinky finger or outside, and sometimes toes too), rocker bottom feet, cleft lip and palate, renal defects, umbilical hernia, cardiac defects
Turner Syndrome
45, X
This is the only survivable monosomy
Wide and webbed neck, widely spread nipples, shorter stature, higher angle of arms, under-developed ovaries, beauty marks (hyperpigmented nevi), hyperlipidemia from birth
Short 4th metacarpal
Different anomalies have been mapped to specific regions
Having only one copy of a region leads to problems
Partial aneuploidy may have partial phenotype
Most autosomes, there are both alleles that are expressed
But X chromosome, one of them are silenced – barr bodies
In turner’s syndrome patients: neuro-cognitive, short statue, gonadal defects- mapped the genes that caused the traits to occur because lack of dose of the other X
Kleinfelter Syndrome
XXY Tall, limbs disproportionately long for trunk Hypogonadism, generally sterile Gynecomastia Low testosterone may lead to low libido
Fragile X Syndrome
Constriction of bottom of X = fragile X
Named because end of X can be lost in cell culture if folate is low in medium
Most common familial cause of mental retardation
Long face, large mandible, outstretched ears, macro-orchidism
Not true recessive or dominant, females affected half as often as males
Long face, prominent jaw, large ears, macro-orchidism
Similar across ethnic groups
