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46 Cards in this Set
- Front
- Back
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Structural Abnormalities
... if chromosome set has normal complement of chromosomal material ... if chromosome set has gained or lost additional material some are stable enough to pass through mitosis and meiosis unaltered -rearranged chromosome must have a functional centromere and two telomeres |
balanced
unbalanced |
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Aneuploidy
... -loss of a single chromosome ... -gain of one chromosome ... -gain of two chromosome |
Monosomy
Trisomy Tetrasomy |
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Which numerical chromosome abnormality is this?
-loss or gain of one or more chromosomes -complete monosomies are only viable for chromosome X -complete trisomies are viable for 13, 18, 21, X and Y -tetrasomies are only viable for X and Y -viability of partial aneusomies dependent on size of unbalanced segment, whether imbalance is monosomic or trisomic and which region of the genome is affected |
Aneuploidy
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Polyploidy (Euploidy)
-addition of one or more complete ... complements -... result from fertilization by two sperm -... results from failure of early mitotic division of the zygote |
haploid
triploidy tetraploidy |
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... : The Control Mechanism for Aneuploidy
-More likely to occur during ... than spermatogenesis -Increases with ... age |
Nondisjunction
oogenesis maternal |
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Nondisjunction
-usual cause of ... -failure of a pair of chromosomes to disjoin properly during one of the two meiotic divisions; most commonly during ... -error during ... results in a gamete with 24 chromosomes containing both maternal and paternal members of the pair -error during ... results in a gamete with an extra chromosome containing both copies of either paternal or maternal chromosome |
aneuploidies
meiosis I meiosis I meiosis II |
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... : Nondisjunction During Mitotic Division
-Presence in an individual or tissue of two or more cell lines -Differ in genetic composition, but are derived from same zygote -Results from ... during mitosis |
Mosaicism
nondisjunction |
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Mosaicism
... also leads to mosaicism, in mitotic division ... is the presence of two or more cell lines in an individual or tissues -result from nondisjunction during early embryonic mitotic division; ... OR -results from the introduction of a de novo mutation in a somatic or early germline cell division; ... severity of disorder due to mosaicism can vary from mild to severe |
nondisjunction
mosaicism numerical structural |
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Down Syndrome:
-95% of cases involve a trisomy of chromosome ... (47,XX,+21 or 47,XY,+21) -Other cases may involve mosaicism and Robertsonian translocations -Incidence increasing with advanced maternal age -Characterized by hypotonia in newborns, distinct dysmorphic facial features, mental retardation and congenital cardiac abnormalities |
21
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Down syndrome
variable etiologies most commonly results from trisomy of chromosome 21 also results from mosaicism and Robertsonian translocation -in patients with ... Down syndrome, cell populations a mix of normal karyotype and trisomy 21 karyotype; variable expression of phenotype -in patients with ... translocations the karyotype is usually 46,XX or 46,XY,rob(14,21)(q10;q10),+21 |
mosaic
Robertsonian |
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Phenotypic Features of Down syndrome
... features evident at birth -brachycephaly, epicanthic folds, protruding tongue, small ears mental retardation congenital heart disease |
dysmorphic
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Phenotypic Features of trisomy ...
-mental retardation and failure to thrive -severe malformation of heart -hypertonic -head has prominent occiput and jaw recedes -characteristic clenching of the fist; second and fifth digit overlap third and fourth -feet have rocker bottom appearance |
18
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Phenotypic Features of trisomy ...
-growth retardation and severe mental retardation -congenital heart defects and urogenital defects -cleft lip and cleft palate -ocular abnormalities -polydactyly -clenched fists -rocker feet |
13
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trisomy 18 and 13:
In both disorders, phenotypes may result from the indicated trisomy or from a variety of rare karyotypes including ... or ... |
mosaicism
translocations |
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The Sex Chromosomes
-X and Y chromosomes -crucial role in sex determination -both male and female have two sex chromosomes -... in female -... in male |
XX
XY |
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The Y Chromosome
-relatively gene ... containing only around 50 genes -high proportion of the genes are related to gonadal and genital development and spermatogenesis -most notable is the ... gene that encodes for the testis-determining factor Also present are two pseudoautosomal regions (present on both Y and X chromosome) -essentially ... on X and Y chromosomes -allow for ... recombination like the other autosomes |
poor
SRY identical homologous |
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X-inactivation
-inactivation of genes on one X chromosomes in somatic cells of female, occurs early in ... -process by which most genes on one of the X chromosomes are ... epigenetically and fail to produce any products -equalizes expression of X-linked genes in the two sexes -females are mosaic with respect to X-linked gene expression as X-inactivation is ... -the inactivated X chromosome is identified cytologically by the presence of a heterochromatin mass called a ... in interphase cells |
embryogenesis
silenced RANDOM Barr body |
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The diploid somatic cells in both males and females have a ... active X chromosome regardless of the total number of X or Y chromosomes
In patients with an extra X chromosomes, any X chromosome in excess of one is ... There can be only one! |
single
inactivate |
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Defining epigenetic features of X inactivation
extensive modification by DNA methylation of ..., restricted to CpG dinucleotides change in ... - both contribute to formation of inactive chromatin -allow for distinguishing between the active and inactive X chromosomes |
cytosines
histone code |
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The XIST Locus
Not all genes on the X chromosome are subject to inactivation -...% escape inactivation and are expressed from both the active and inactive X chromosomes -additional ...% show variable inactivation |
15
10 |
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XIST (inactive X (Xi)-specific transcripts) gene
-key master regulatory locus for X inactivation -expressed only from allele on ... -transcriptionally silent on ... in males and females -X-inactivation cannot occur without it |
inactive X
active X |
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Non-random X Inactivation
X inactivation normally ... in female cells and leads to mosaicism -one population expresses alleles one X chromosome or the other ... pattern of inactivation works to minimize the clinical consequences of a particular chromosomal defect - does not necessarily eliminate |
random
non-random |
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When karyotype involves a structurally abnormal X
1. Unbalanced structural abnormalities of an X chromosome (deletions, duplications, isochromosomes) -structurally abnormal X is always ... 2. X:autosome translocations A. ... translocation -normal X chromosome is preferentially inactivated B. ... translocations -only the translocation product carrying the X inactivation center is present; this chromosome is inactivated -normal X is always ... |
inactivated
Balanced Unbalanced active |
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Sex Chromosome Abnormalities
can be either ... OR ... can be either present in all cell OR mosaic X and Y ... relatively common phenotypes generally ... severe than comparable autosomal disorder WHY? X-inactivation and low gene content of Y chromosomes -... are commonly observed in live births: Klinefelter syndrome (47,XXY), Trisomy X, and 47,XYY syndrome -... is most commonly observed in spontaneous miscarriages: Turner syndrome (45,X) |
structural
numerical aneuploidies less Trisomies Monosomy |
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which syndrome is this?
Karyotypes: -47,XXY -48,XXXY -mosaics 46,XY/47,XXY and other combinations Phenotypic Features -tall and thin, relatively long limbs -verbal comprehension and ability below normal -normal until puberty -hypogonadism -infertile; failure of germ cell development -gynecomastia |
Klinefelter Syndrome
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which syndrome is this?
not associated with an abnormal phenotype; tendency to be tall -cannot be distinguished from normal 46,XY males nondisjunction at meiosis II producing YY sperm normal fertility IQ scores 10-15 points below average -attention deficits, hyperactivity and impulsiveness |
47,XYY Syndrome
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which syndrome is this?
Karyotype: -45,X -46,X,i(Xq) -45X/46,XX mosaic -45X/46,i(Xq) mosaic -additional abnormalities observed Phenotypic Features -edema of hands and feet observed at birth -short stature -unusual facies -webbed neck -increased frequency of renal and cardiovascular problems -normal intelligence, yet decreased social cognition |
Turner Syndrome
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which syndrome is this?
-although slightly above average stature, NOT phenotypically abnormal -fertile -significant proportion have learning deficits -10-20 point drop in IQ -display abnormal behaviors; most noticeable during transition from adolescence to adulthood |
Trisomy X (47,XXX)
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What is this?
“outside” of genetics Refers to any factor that can affect gene function without changing the actual DNA sequence of genotype -heritable X-inactivation and Imprinting are both under the influence of epigenetic effects -DNA methylation -Chromatin structure -Histone Code |
epigenicity
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Genetic Imprinting
expression of phenotype dependent on whether mutant allele has been ... or ... inherited normal process caused by ... in chromatin that occur in the germline of one parent but not the other at characteristic location in the genome ... effects (influence gene expression with chromosomal regions without changing primary DNA sequence) -covalent modification of DNA via methylation -modification or substitution of histone code altering chromatin structure -reversible |
maternally
paternally alterations Epigenetic |
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Conversion of imprinting
takes place during ... -marks certain genes as coming from either the mother of the father after conception -imprints control gene expression within imprinted region in some or all somatic tissues of embryo persists throughout ... ... at the germline to be re-imprinted |
gametogenesis
adulthood erased |
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... - Phenomenon that results in different expression of alleles depending on parent of origin
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Genomic Imprinting
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Map of Imprinted Regions in the Human Genome
- at least a dozen if not hundreds of gene that are ... -some regions contain a single imprint gene others contain clusters |
imprinted
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REMEMBER! If a gene is imprinted it (is? or is not?) expressed
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is NOT
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Hallmark of an imprinted gene
-only one allele is expressed (the ...), either maternal or paternal, in relevant tissue -... loci (majority of loci) are expressed from both maternal and paternal alleles in each cells |
non-imprinted
non-imprinted |
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which syndrome is this?
-mental retardation -obesity -excessive and indiscriminate eating habits -small hands and feet -short stature -hypogonadism |
Prader Willi Syndrome
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which syndrome is this?
-unusual facial appearance “overly happy” -severe mental retardation -short stature -spasticity -seizures |
Angelman Syndrome
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Best examples of genomic imprinting found in Prader Willi Syndrome and Angelman Syndrome
Etiology -in 70% of cases in both syndromes, there is a deletion involving the proximal long arm of chromosome ... (15q11-q13) -In Prader Willi Syndrome, the deletion is inherited from the ..., ... locus imprinted -In Angelman Syndrome, the deletion is inherited from the ..., ... locus imprinted |
15
father maternal mother paternal |
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which of the following can result in down syndrome?
trisomy 21 rob(14;21)(q21;q21) |
All answers are correct
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How many X chromosomes are inactivated in 47,XYY syndrome?
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0
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Which type of inheitance displays a pattern where children of an affected female are all affected and children of an affected male are all unaffected?
1. Autosomal dominant 2. Autosomal recessive 3. Mitochondrial 4. X-linked dominant 5. X-linked recessive |
Mitochondrial
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Which types of inheritance takes into account the influence of environmental factors?
1. Multifactorial 2. Polygenic 3. Unifactorial (Mendelian) |
multifactorial
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Individuals with Hemophilia have differeent % activity of either Clotting Factor VIII or IX impacting the severity of the disease. This is an example of
1. Anticipation 2. Incomplete dominance 3. Incomplete penetrance 4. Pleiotrpy 5. Variable expression |
variable expression
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Two diseases are caused by mutations in the same gene. The milder of the two diseases is most likely caused by
1. an insertion that causes a frameshift. 2. a missense mutation. 3. a nonsense mutation. |
a missense mutation
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What type of genetic hetergeneity accounts for the existence of two diseases resulting from mutations in the same gene?
1. Allelic heterogeneity 2. Locus heterogeneity 3. Phenotypic (clinical) heterogeneity |
phenotypic heterogeneity
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In HD, an early age of onset is associated with
1. low repeat abnormal alleles. 2. moderate repeat abnormal alleles. 3. high repeat abnormal alleles. |
high repeat abnormal alleles
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