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71 Cards in this Set

  • Front
  • Back
hereditary factor that interact with the environment to determine the trait
alternative forms of a gene occupying a given chromosomal locus
There may be multiple normal and abnormal alleles of any particular gene
a specific location of a gene on a chromosome. Since human chromosomes are paired, every person has two alleles at each locus
genetic constitution, representing allelic makeup of an individual
end results of genetic and environmental factors giving the clinical picture or the observed expression of the gene
a person with two identical alleles at a single locus
Alleles may be either normal or abnormal
a person with two different alleles at a single locus
Usually one normal one mutant allele
A person is called a carrier
Compound heterozygote
an individual with two different mutant alleles at one locus
double heterozygote
an individual with two mutant alleles, each at a different locus
autosomes (nonsex chromosomes)
when two loci are on the same chromosome
occurence of two or more genetic loci in such close physical proximity on chromosome that they are more likely to segregate together during meiosis
phenotype expression of the mutant gene (all or nothing phenomenon)
% of persons with a mutant allele who are affected
the degree of (continuous) expression of particular allele in a person
the production of multiple phenotypes by a single gene or gene pair
is mimic of a phenotype produced by specific genotype (may be caused by environmental factors)
Genetic heterogeneity
different mutations at the same locus or different loci result in similar clinical phenotype
Sex influenced
severity of the disease depending on the sex of the person carrying a mutant gene(s)
Hemochromatosis (AR) in males
CAH (AR) in females
Autosomal recessive inheritance
The trait spread horizontally
There is no sex predilection
If the trait is rare, parental consanguinity is increased
Autosomal dominant inheritance
Transmission of the trait is from generation to generation (without skipping)
Except for new mutation every affected child will have an affected parent
The two sexes are affected in equal numbers
X-linked inheritance (recessive)
The trait is transmitted by normal heterozygous mothers :
Hemizygous affected males have normal sons and daughters.
All daughters of affected father are obligatory carriers
X-linked inheritance (dominant)
There is no male-male transmission
All female offspring of affected males will be affected
Germinal mosaicism
The presence of two gametes carrying normal and mutant alleles
May change recurrence risk for the offspring
Mitochondrial inheritance
Types of mutations: point /deletions
Predominantly maternal inheritance
presence of normal and mutant DNA in the same cell
presence of only normal or only mutant DNA in the same cell
Uniparental disomy
The presence in the diploidal cell line of a both chromosomes of a given pair from only one parent
Possible consequences:
- imprinting of sigle genes or chromosome region
- homozygosity for mutant allele
Genomic imprinting
Differential expression of a gene depending on whether it was inherited from the mather or the father  epigenetic control of gene expression
Genomic imprinting/UPD & microdeletion syndromes
Prader- Willi syndrome (Del 15q11-q13) -70% pat
Angelman syndrome (Del 15q11-q13) -70% mat
Genetic linkage
Refers to loci not to alleles
The phase of the linkage
Family studies are necessary
Measurements of the linkage
chromosomal distance
recombination fraction = cM
lod score
coupling = cis
repulsion = trans
Linkage: measurements
The recombination fraction between two loci is the probability of the occurence of crossing over between loci
LOD score
Conventional chromosomal banding
g-banding (trisomy 13)
gene fusion
Numerical abnormalities
Polyploidy (3n,4n,5n)
Aneuploidy (2n-1,2n+1,2n+2)
Structural abnormalities
Terminal Deletion
Interstitial Deletion
Isochromosome (iso-q,iso-p)
Ring Chromosome
Robertsonian translocation
Reciprocal translocation
Complex inheritance
Does not follow simple Mendelian pattern
The recurrence risk depends on:
Degree of relationship with the proband
Severity of the proband’s disease
Number of affected individuals in the family
Sex of the proband (more commonly affected)
Segregation analysis
statistical comparison (binomial therom) of frequency and distribution of affected and unaffected individuals in families to determine the most likely mode of inheritance
Association analysis
statistical comparison to determine if a particular form of DNA polymorphism occurs more frequently in subjects with a phenotype of interest
Linkage analysis
analyze the distribution of loci within families to determine if a particular region of genome contains a gene related to the phenotype of interest
Linkage mapping
crossover frequency indicated the distance of separation on a chromosome
greater distance more frequency of crossing over, less likely to be linked
LOD score
Recombinant frequency
rearrangement of loci
equivalent to 'genetic map unit'
50% RF = not linked
0% RF = linked
Linkage disequilibrium
study of population genetics for the non-random association of alleles at two or more loci, not necessarily on the same chromosome
LOD score
logarithm of odds
3 LOD = linked
-2 LOF = not linked
failure to disjoin in mieosis I or II
Molecular technique (FISH)
in situ hybridization
cytogenetic technique which can be used to detect and localize the presence or absence of specific DNA sequences on chromosomes
florescent probes with chromosomal similarity
Northern blot
Southern blot
Western blot
W - protein
triploidy 3n
tetraploidy 4n
non-disjunction during meiosis
trisomy 2n+1
monosomy 2n-1
Examples of Aneuploidy
13 (Patau)
18 (Edwards)
21 (Down)
XXY (Klinefelter)
X-monosomy (Turner)
Unbalanced structural mutations
deletion - terminal/interstitial
isochromosome (Turner)
Balanced structural mutations
paracerntric (includes centromere)
pericentric (change in arm)
recipricol (exchange of material between nonhomologous chromosomes)
Robertsonian (long arms of two acrocentric chromosomes fuse at the centromere and the two short arms are lost)
13, 14, 15, 21, and 22
Dynamic mutation
unstable heritable element where the probability of mutation is a function of the number of copies of the mutation
Examples of dynamic mutations
Fra X
Huntington disease
Dystrophia myotonica
Ataxia Friedreicha
Gene mutations
point mutation
frameshift mutation
Point mutations
missense (AA substitution)
nonsense (premature stop)
silent/synonymous (no change)
RNA processing/transcription
Frameshift mutations
'Hotspot' mutations
transition (T->C, A->G)
transversion (purine->pyrimidine)
Functional cloning
Using information about the function of a known protein that could be involved in a genetic disease (limited approach)
Positional cloning
Using only information about the gene's approximate chromosomal location obtained from gene mapping
Cystic fibrosis
AR disorder pf epithelial ion transport
mutations in CFTR gene: cAMP regulated excretion of chloride and inhibition of sodium uptake
"salty-baby syndrome"
Duchenne Muscular Dystrophy
X-linked panethnic progressive myopathy
mutations in DMD gene that encodes dystrophin
predominatly large deletions and large duplications
Fragile X Syndrome
X-linked mental retardation disorder
mutations in FMR1 on Xq27.3
expansions of (CGC)n
premutation -> full mutation
Huntington Disease
AD panethnic progressive neurodegenerative disorder
mutations in HD gene
expansion of polyglutamine-encoding CAG respeat sequence
age of onset is proportional to number of HD repeats
Prader-Willi Syndrome
panethnic developmental disorder, hypogonadism, obesity
loss of expression of genes on paternally derived 15q11-q13 (70%)
maternal uniparental disomy (25%)
genetic imprinting
Sickle Cell Anemia
AR Beta-subunit missense mutation (Valine for Glutamine)
decreases solubility of deoxygenated hemoglobin
anemia, failure to thrive, splenomegaly
Turner Syndrome
female monosomy X
panethnic disorder
complete or partial absence of second X chromosome in females
75% sperm lacking sex chromosome
Y chromosome differentiation
ovarian pathway is followed unless TDF (testis-determining factor) is present
Leydig cells, siminiferous tubules, testes, Sertoli cells, mesonephric ducts
X chromosome differentiation
absence of TDF on SRY (sex-determining region on the Y)
ovaries, paramesonephric ducts
X chromosome inactivation
formation of a Barr body
DNA methylation
encoded XIST prevents expression of TSIX