Flashcards in Ch9: Genetics Deck (277):
Disorders related to single gene usually follow what inheritance pattern?
Two types of single gene mutations?
2. Non-classic inheritance
What is a mutation?
Permanent change in DNA of an organism
What is a genome mutation?
Loss or gain of whole chromosomes
What is a chromosomal mutation?
Structural changes to chromosomes
What are gene mutations?
Change at gene level
What are the two categories of gene mutations?
1. Point mutations
2. Frameshift mutation
What are the two types of point mutations?
1. Nonsense mutation
2. Missense mutation
What are the two types of frameshift mutations?
Trinucleotide repeat mutations occur within coding or non-coding regions?
What is the longest chromosome?
Which is the shortest chromosome?
What is a balanced reciprocal translocation?
exchange of material between nonhomologous chromosomes
What is a Robertsonian translocation?
nonreciprocal translocation involving two homologous (paired) chromosomes or non-homologous chromosome
What is an isochromosome?
chromosome that has lost one of its arms and replaced it with an exact copy of the other arm.
What is a paracentric inversion?
reversal of the normal order of genes in a chromosome segment involving only the part of a chromosome at one side of the centromere
What is a pericentric inversion?
inversions include the centromere and there is a break point in each arm
How does a ring chromosome form?
chromosome whose arms have fused together to form a ring
Hemoglobin S is the result of what type of mutation?
Point mutation causing a missense mutation
What is the exact change in hemoglobin S?
GAG becomes GUG which encodes valine instead of glutamic acid
What type of mutation is beta thalassemia?
Point mutation causing a nonsense mutation.
What type of mutation is the ABO O allele?
Frameshift mutation from a single base deletion
Hexosaminidase A/Tay Sachs is the result of what?
Frameshift mutation caused by four base insertion
Cystic fibrosis is the result of what?
Three base deletion that does NOT cause a frameshift
Fragile X syndrome is the result of what?
CGG triplet repeat
Friederich ataxia is the result of what?
GAA triplet repeat
Huntington's disease is the result of what?
CAG triplet repeat
Myotonic dystrophy is the result of what?
What is myoclonus epilepsy the result of what?
12 repeat: CCCCGCCCCGCG
What is a mendelian disorder?
Genetic disorder of large effect caused by a single gene mutation
What is the one common X-linked dominant disorder?
Vitamin D resistant rickets
3 mendelian disorder types
1. Autosomal dominant
2. Autosomal recessive
3. X-linked recessive
Autosomal dominant is a disorder manifested in what genotype?
When do autosomal dominant disorders present?
Onset delay until adulthood
Can autosomal dominant disorders spontaneously occur in the germline?
What modifies the expression of autosomal dominant genotype?
1. Reduced penetrance
2. variable expressivity
What does the mutated gene usually encode for in autosomal dominant?
Control points in metabolic pathways
Key structural proteins
Autosomal recessive disorders are manifested only in what genotype?
Siblings in AR disease have what chance of being affected?
Of being carriers?
1 in 4 chance of being affected
1 in 2 chance of being a carrier
If a low frequency gene mutation begins to appear, what does this suggest?
Population is consanguineous
Which has more uniform expression, autosomal dominant or recessive?
Is complete penetrance common in AR?
When does onset of autosomal recessive occur?
Early in life
Can spontaneous mutations occur of autosomal recessive genes?
Yes, but takes awhile to present (several generations)
Autosomal recessive genes usually encode for what?
What protects us against a heterozygous autosomal recessive genotype?
The normal gene will make enough enzyme to be at functioning level
X-linked recessive disorders require how many abnormal X chromosomes in females?
X-linked recessive disorders require how many abnormal X chromosomes in males?
Who transfers the X-linked recessive gene?
Who receives the X-linked recessive gene?
Sons (1 in 2 chance)
What can lead to expression of an x-linked recessive phenotype in females?
How does an affected father of an x-linked recessive disorder pass on the mutation?
All daughters will be carriers
What is codominance?
When two different gene alleles are fully expressed together.
What are examples of codominance? (2)
2. Blood groups
Codominant Mendelian disorders occur when?
When both normal and mutant gene are fully expressed
What are examples of some codominance disorders? (2)
2. Sickle cell anemia
What is penetrance?
The measure of how much a Mendelian disorder is phenotypically expressed.
What is it called when all individuals with a mutation express the phenotype?
What is it called when some affected individuals are phenotypically normal?
What is variable expressivity?
Degree of phenotypic change seen in affected individuals.
Example of variable expressivity?
Neurofibromatosis. Some individuals have cafe au lait macules and some have widespread neural tumors and deformities
What is polymorphism?
Existence of more than one normal allele of a gene.
What are examples of polymorphisms? 2
1. histocompatibility genes
2. Blood group genes
What are the most common form of polymorphisms?
SNP's occur in coding regions how often?
What is pleiotropism?
Ability of a single mutation to have more than one phenotypic effect?
What are two examples of pleiotropism?
1. Marfan syndrome
What is genetic heterogeneity?
Ability of different gene muations to cause the same phenotypic change.
Example of genetic heterogeneity? (2)
1. Retinitis pigmentosa
2. Childhood deafness
What is the phenotype?
Physical appearance or biochemical characteristics as distinguished from its genotype
What is genotype?
genetic makeup of an organism as distinguished from its physical characteristics
Two types of non-protein producing genes?
What are miRNA?
small RNA molecules that are further shortened, unwound to single RNA strands, and coupled with proteins.
The RNA-induced silencing complex interacts with what?
To what effect?
Cleave or suppress translation of mRNA
If child has an autosomal dominant mutation but neither parent does, what happened?
Are autosomal dominant mutations usually loss of function or gain of function?
Two main characterizations of AD disorders?
1. variable expressivity
2. reduced penetrance
Autosomal dominant disorders in the nervous system include? 4
1. neurofibromatosis (von Recklinghausen)
2. Huntington's diseas
3. myotonic dystrophy
4. tuberous sclerosis (bourneville's disease)
AD disorders in urinary system?
Adult polycystic kidney disease
Gastrointestinal AD disorder?
Familial polyposis coli
Hematopoietic AD disorder? 2
1. hereditary spherocytosis
2. von willebrand disease
Neurofibromatosis Type 1 is known as what?
von Recklinghausen disease
What percentage of NF-1's are spontaneous mutations?
Which is more common, Type 1 or Type 2 NF?
Type 1 NF
What is the cause of NF-1
Defect of NF-1 gene on chromosome 17q11
NF-1 is what type of gene?
What does it produce?
Tumor suppressor gene
Clinical features of NF-1? 3
2. Cafe au lait macules
3. Lisch nodules
What are the 4 types of neurofibromas in NF-1? Which is the one to watch for?
3. deep tissue
4. plexiform: (WATCH THIS ONE)
Malignant tumors show up in NF-1 what percentage of the time?
What other things can NF-1 produce? (4)
What are lisch nodules?
Brown irregular discolorations in the iris
NF-2 has what clinical features? (5)
1. Bilateral acoustic neuromas
2. Multiple meningiomas
4. Cafe au lait macules
5. NO Lisch nodules
NF-2 gene is found where?
What does it produce?
Hereditary spherocytosis is developed how?
auto-hemolytic anemia characterized by the production of red blood cells that are sphere-shaped rather than bi-concave disk shaped (donut-shaped), and therefore more prone to hemolysis
AD skeletal disorders include what? 4
3. osteogenesis imperfecta
Metabolic AD disorders? (2)
1. familial hypercholesterolemia
2. acute intermittent porphyria
Marfan syndrome is due to what defective protein?
Where is this gene found?
Function of this protein normally?
Provide stability to elastic tissue
Overall, Marfan is a disorder of what?
What do you see in marfan syndrome? 7
1. aortic dilatation leading to valve incompetence
2. cystic medial necrosis leading to aortic dissection
3. Mitral valve prolapse
4. Increased stature
6. Dislocated lens (ectopia lentis)
7. Premare aging due to mucopolysaccharide deposition
Ehlers-danlos syndrome involves how many diseases?
Ehler-danlos syndrome exhibits what type of inheritance?
What collagen pathways are mutated in Ehlers-Danlos? 3
How does ehler danlos present?
1. Very stretchable skin
2. hypermobile joints
hypotonia at birth
3. epicanthal folds and blue sclerae in eyes
What people do you see with Ehlers-Danlos?
Which is the most common mendelian disorder?
What is the main cause of familial hypercholesterolemia?
Defective LDL receptor which regulates cholesterol metabolism
Clinical manifestations of familial Hypercholesterolemia?
High levels of total and LDL cholesterol
What are the five mutations that can result in hypercholesterolemia?
Class I: Can't synthesize LDL receptor
Class II: Can't transport LDL receptor to membrane
Class III: Can't put LDL receptor into plasma membrane
Class IV: Can't get LDL receptors to cluster in coated pit
Class V: Can't recycle LDL receptors after use
Xanthomas are representative of what?
Xanthelasma are representative of what?
Somewhat with hypercholesterolemia familial
Cystic fibrosis is what type of disorder?
Autosomal recessive systemic disorder of exocrine glands that affects mucus-secreting and eccrine glands
The defects in CF involve what abnormality?
What does this result in?
Abnormally thick mucus that can cause obstruction of excretory ducts which is really harmful in lungs and pancreas
What reputation does CF have?
Most common fatal autosomal recessive disease affecting the Caucasian population
Why does CF occur?
Defect in c-AMP-regulated ion transport across apical membranes of affected epithelial cells
How does CF affect the sweat glands?
What does this mean clinically?
Failure of resorption of chloride in duct epithelial cells which results in high chloride levels in sweat.
the pilocarpine sweat test in which a value of sweat chloride above 60 mEq/L (normal being 10 mEq/L), along with symptoms consistent with CF, is essentially diagnostic
How does CF affect the lungs and pancreatic duct cells?
Failure to transport chloride into lumen of airways and ducts which is coupled with increase sodium resorption which results in very thick viscid secretions that begin to obstruct. In the lungs this provides great environment for pseudomonas
The CF gene has been localized to where?
What is the gene product?
Chromsome 7 long arm
CF transmembrane conductance regulator (CFTR) which is a chloride channel that can't be activated by cAMP
Heterozygous CF patients will display what?
Resistance to diarrheal diseases like cholera
How many CF mutations exist?
Which is the most common at 70%?
Deletion of a 3 base pair encoding phenylalanine (Delta F508)
How does CF affect the pancreas early on? 2
What follows? 3
What happens later?
1. Cystic dilatation
2. Direct plugging of exocrine glands and ducts with eosinophilic secretions
Acinar atrophy with rupture
Fatty and fibrous replacement of exocrine pancreas that spares islet cells usually
How does CS begin in lungs? (2)
What does long term CF give rise to? (3)
1. Plugging of submucosal tracheal mucous glands and ducts
2. Bronchioles become distended with mucus
How does cystic fibrosis begin in liver?
What is seen resulting from this
Bile duct hyperplasia due to mucus plugging bile canaliculi
Focal biliary cirrhosis and diffuse hepatic nodularity
CF in salivary glands show what?
Glandular dilatation and atrophy
CF in the reproductive glands show what?
Obstruction of Wolffian duct derivatives like epididymis and vas deferens leads to azoospermia and infertility in 95% of males
15% of infants with CF present with what?
What happens in this?
Obstruction of terminal ileus with risk of perforation and peritonitis
CF is discovered when?
Because of what?
between 12 months and 2 years
Malabsorption symptoms due to pancreatic insufficiency
What causes 80 to 90% of deaths in CF? 2
Obstructive pulmonary disease
Persistent pulmonary infections
What is current therapy for CF? 3
How long can CF patients live now?
What is in the works for CF therapy?
1. Pancreatic enzymes
2. Fat soluble vitamins
3. Antibiotics for pulmonary infections
50% live past 31
Normal DNA injected into respiratory epithelial cells
Sickle cell anemia results from what type of mutation?
Inheritance of a single mutant sickle cell alelle results in what?
Sickle cell Trait
Sickle cell trait gives the person what?
Protection to malaria
Sickle cell disease forms can also include what? (2)
1. Sickle-hemoglobin C disease
2. Sickle-beta thalassemia
How many genes make up hemoglobin?
4 alpha genes (2 HBA1 and 2 HBA2): Ch 16
2 beta genes: Ch 11
Hemoglobin A has what chains?
What percentage of adult Hb is this form?
2 alpha and 2 beta
Hemoglobin A2 has what chains?
What percentage of adult Hb is this form?
Hemoglobin F has what chains?
Hemoglobin S has what chains?
Two mutated Beta
Hemoglobin AS has what chains?
One mutated Beta
What hemoglobin genotypes are in sickle cell trait?
Hemoglobin C has what chains?
Two mutated beta
Hemoglobin SC has what chains?
1 Beta S mutation
1 Beta C mutation
Hemoglobin E has what chains?
Two mutated beta (E mutation)
How do sickle cells affect the blood?
1. Increased adhesion causes infarcts in the kidney
2. Increased hemolysis in spleen that can result in autosplenectomy
Phentylketonuria is what type of inheritance?
PKU affects what people?
PKU is due to a severe lack of what enzyme?
Phenylalanine hydroxylase causing hyperphenylalaninemia and PKU
No phenylalanine hydroxylase means what?
Can't convert phenylalanine to tyrosine so metabolites form in urine and sweat
How does PKU present at birth?
Doesn't appear at birth, but within a few weeks have increasing plasma levels of phenylalanine and toxic metabolites
Treatment of PKU is what?
Restrict ingestion of foods with phenyalanine during infancy and childhood
PKU results in what within 6 months if it is not treated? 4
PKU screening is performed when? What test?
Neonatal by the Guthrie test
What is maternal PKU results from what? 2
1. teratogenic effects of phenylalanine
2. metabolites that cross the placenta in a female adults with PKU who don’t follow a phenylalanine restricted diet during pregnancy
In PKU in adults, do the affected adults show symptoms?
Can they give up low Phenylalanine treatment?
Affected adults have no apparent adverse affects from elevated levels of phenylalanine and its metabolites after CNS development is complete
Yes, but NOT if pregnant
Maternal PKU anomalies include? (6)
Low birth weight
98% of PKU is due to a mutation in what?
Galactosemia is what inheritance?
Galactosemia is the ability to do what?
Convert galactose to glucose because do not have galactose-1-phosphate urydil transferase
Clinical presentation of galactosemia? (6)
1. hepatomegaly and jaundice
3. Non-specific CNS changes
4. failure to thrive
How can galactosemia be prevented?
No galactose in diet until age 2
Lysosomal storage disease results from what?
Lack of lysosomal enzymes essential for normal function of lysosomes results in lysosomes storing non-metabolized products
Example of glycogenoses?
Example of sphingolipidoses?
Example of sulfatidoses?
Example of mucopolysaccharidoses?
Tay sachs results from what enzyme complex being mutated?
What does this cause?
Deficiency of Hexosaminidase A alpha subunit
The GM2-ganglioside accumulation of TaySachs is where?
Neurons of CNS and ANS
Retinal cherry red spot
Tay-Sachs disease is most common with what population?
When do they die?
Death by 2-3 years
What does Niemann Pick disease result from?
Accumulation of sphingomyelin and cholesterol
What types of Niemann-Pick are there?
Which is most common?
Which is most common in Ashkenazi?
A, B, C
C most common
A and B
Type A of Niemann Pick is known as what form?
What symptoms? (4)
Severe infantile form
Neuronal death with resultant brain shrinkage
Retinal cherry spot
Hepatosplenomegaly and lymphadenopathy
Death at age 1-3
Type C Niemann Pick has what gene affected?
What does this gene control?
Heterogeneous Niemann Pick Type C shows what? 3
Hydrops fetalis and still birth
Chronic form with progressive neurologic damage
Gaucher disease is characterized by mutation in what gene?
What does this lead to?
Decreased levels or activity of this enzyme
Three subtypes of Gaucher disease?
Type I gaucher disease is involved with what cells?
Mononuclear phagocytes, NOT the CNS.
What changes are common in Type I gaucher?
Which population has it the most
Spleen and skeletal
Eastern European Jews
What is Type II and Type III Gaucher's disease known as?
Type II: Infantile acute cerebral form
Type III: Intermediate form
All forms of Gaucher have elevated levels of what enzyme?
Type I Gaucher has what appearance under microscopy?
Crumpled tissue paper
Hunter and Hurler syndromes are examples of what?
All mucopolysaccharidoses have what inheritance?
The one exception?
Hunter: X-linked recessive
Common features of mucopolysaccharidoses? 4
Coarse facial features
Clouding of the corneas
What is glycogenoses the result of?
metabolic defect in the synthesis or catabolism of glycogen
What are the three main types of Glycogenoses?
Hepatic type (von Gierke disease, type I)
Myopathic type (McArdle syndrome, type V)
Miscellaneous types (Pompe disease, type II)
Pompe is due to what deficiency?
lysosomal Acid maltase
Hepatic glycogen storage disease will cause what?
Feeling hungry and not nourished
Myopathic glycogen storage disease will cause what?
McArdle is due to what deficiency?
von Gierke's disease is due to what deficiency?
Pompe has characteristics of what two sets of disorders?
1. glycogen storage
2. lysosomal storage
In pompe, what happens to the glycogen?
Accumulates in organs, especially the heart, and causes death
What is the heredity of alkatonuria?
Alkaptonuria is caused by what?
lack of homogentisic oxidase causing build-up of homogentisic acid
In alkaptonuria, where does the homogentisic build up go?
1. Excreted in urine which will stain black upon staining
What is ochronosis?
where is this seen the most?
homogentisic acid binds to collagen in tissues imparting black-blue pigmentation to these tissues
ears, nose, cheeks, joints
Fragile X is different from the other x linked recessive diseases how?
It's seen as X-linked recessive and x-linked dominant. It's a triple nucleotide repeat that doesn't play by the rules.
What are all the possible disorders located on X chromosome
Duchenne Muscular Dystrophy
Becker Muscular Dystrophy
Hemophilia A & B
Glucose-6-phosphate dehydrogenase deficiency
Chronic granulomatous disease
Fragile X syndrome
Chronic granulomatous disease
Multifactorial inheritance results from what?
combined actions of environmental influences and the additive effects of two or more mutant genes
Risk of a multifactorial inheritance increases with what?
increases with the number of abnormal genes inherited
Normal phenotypic multifactoral characteristics include? 4
1. hair color
4. skin color
in multifactorial inheritance, is the rate of recurrence the same for all the siblings?
Disorders/defects associated with multifactoral inheritance include? 7
cleft lip/palate, congenital heart disease, coronary heart disease, hypertension, gout, diabetes mellitus and pyloric stenosis
What is a karyotype?
An arrangement of chromosomes that is obtained from freshly obtained dividing cells such as leukocytes, fibroblasts, or amniocytes
Cytogenetic notation of normal female?
Cytogenetic notation of female with down's?
Cytogenetic notation of female with Turner's?
What does the notation mean (45,XX der(13,14)?
Designates a “derived” (der) chromosome formed from the fusion of the long arms of chromosomes 13 and 14 with loss of the short arm material from both chromosomes
A derived chromosome can only occur with what chromosomes?
The five acrocentric (minimal short arms) chromosomes: 13, 14, 15, 21, 22
What does 46,XX,del (5p) mean?
deletion of DNA from the short arm of chromosome
What does 46,XY t(9;22)(q34;q11) mean?
reciprocal translocation between chromosomes 9 and 22. This forms the abnormal BCR-ABL gene seen in chronic myelogenous leukemia. Also known as the Philadelphia chromosome
What does 46,XY inv(16), t(16;16) mean?
Designates an inversion translocation in which a segment of chromosome 16 DNA is reversed or inverted within the chromosome
A paracentric inversion involves the centromere, yes or no?
A pericentric inversion involves the centromere, yes or no?
Karyotyping involves looking at chromosomes when?
How is this accomplished?
What stain is used?
metaphase portion of mitosis
mitosis—use the drug colchicine to stop the mitotic cycle in metaphase
Can chromosomes be distinguished from each other in karyotyping? How?
They have different banding patterns
What does q mean?
What does p mean?
Cytogenetic disorders are defined how?
Disorders that involve abnormal numbers or structures of chromosomes per classic karyotyping
What is diploid for humans?
46XX or 46XY (2N)
What is triploid for humans?
69XXX, etc, (3N)
What is aneuploid for humans?
Not Diploid or Polyploid (3N, 4N, etc.)
What is monosomy
What is trisomy?
Loss of chromosome
Gain of chromosome
FISH studies can be used to identify what?
Do you need dividing cells?
What must you know before starting?
specific DNA sequence in interphase nuclei as well as in karyotyping studies
specific DNA sequences to design the probes, which are labeled with a fluorescing compound
What is mosaicism?
presence of two or more populations of cells with different genotypes in a single individual
Examples of mosaicism? 3
1. normal cells and monosomy
2. normal cells and trisomy
3. normal cells with specific gene mutation
Monosomy and trisomy usually result from what?
nondisjunction of chromosomes during gametogenesis (meiosis)
Mosaicism results from what
errors in mitosis in the zygote
What are the 3 main trisomies?
How common is each
21: Downs (most common)
13: Patau (least common)
What is Edwards karyotype?
47, XY, +18
What are some common Edwards symptoms? 6
structural heart defects at birth
What is Patau karyotype?
47, XY, +13
What are some common Patau symptoms?
Mental retardation and motor disorder
Polydactyly (extra digits)
What is the MOST common of the chromsomal disorders?
Down syndrome risk for child increases with what?
Increased maternal age
Most common cause of trisomy 21 is what?
meiotic nondisjunction; 47,XX or XY, +21 (95%)
Three causes of trisomy 21? 3
1. Meiotic nondisjunction
2. Robertsonian translocation
Clinical findings of down's include? 8
1. Flat facial profile
2. Oblique palpebral fissures
3. Epicanthic folds
4. Congenital heart disease (40%), especially endocardial cushion defects
5. Acute leukemia (10-20X increased risk)
6. GI atresia,
7. Alzheimer disease (in patients older than 40),
what is the Lyon hypothesis of cytogenetic disorders invovling sex chromosomes?
Only one active X chromosome is needed and the other copy(ies) are inactivated and become Barr bodies.
Can you have mosaics with sex chromosome disorders?
yes, if different X chromosomes are inactivated in different tissues. Some maternal cells may have both X chromosomes active
How do placental mammals and marsupial mammals differ in terms of X chromosome disorders?
In placental mammals either X chromosome may be inactivated, but in marsupial mammals the paternal X chromosome is preferentially inactivated
Normaly, sex chromosome disorders cause what?
subtle, chronic problems relating to sexual development and fertility
The higher the number of X chromosomes, the greater the likelihood of what?
What is Klinefelter's syndrome?
Male hypogonadism that occurs when there are two or more X chromosomes and at least one Y chromosome (needed for the male phenotype
What is the classic form of Klinefelter's?
What are some mosaic examples of Klinefelter's?
Manifestations of klinefelter's? 10
1. Slightly low IQ,
2. increased risk of mental retardation with additional copies of the X chromosome
3. Atrophic testes,
8. female distribution of fat and skeletal abnormalities
9. Increased breast cancer
10. autoimmune disorders
Full chromsomal monosomy of any sort will resort in what?
Trisomy X entails what?
Syndrome in which females have an extra X chromosome - 47 XXX - two Barr bodies in cells
Trisomy X patients are at risk for what? (3)
Speech, language and learning disabilities
Tall stature and poor muscle tone
Most trisomy X patients have what symptoms?
Just mild effects and will never be diagnosed
XYY Males have what karyotype?
47,XYY or 48,XYYY
XYY males have what symptoms? (3)
3. antisocial behavior
Turner syndrome results from what?
complete or partial monosomy of the X chromosome
Turner syndrome is characterized primarily by what?
hypogonadism in phenotypic females
Turner syndrome clinical findings? (8)
Coarctation of aorta
Webbing of the neck
Broad (shield) chest with widely spaced nipples
Main symptoms of Turner syndrome? (4)
Nonmedelian inheritance includes what types of disorders? 4
1. Triplet repeat
2. genomic imprinting
3. mitochondrial mutations
4. gonadal mosaicism
Triplet repeat mutations are caused by what?
Caused by long segments of repeating nucleotides
Genomic imprinting involves what?
preferential down regulation (turning off) of genes
What are premutations?
increased numbers of trinucleotide repeats, but not enough to meet characteristics of full mutation
What is a full mutation?
Additional triple repeats with full spectrum of phenotypic changes
What is anticipation?
Clinical features worsen with each successive generation as a result of amplification of trinucleotide repeats during oogenesis or spermatogenesis
What is Sherman's Paradox?
Risk of having the full mutation and increased phenotypic changes depends on the position of the individual in the pedigree
Triplet repeat mutations include? (4)
Fragile X syndrome
What makes Huntington's disease special from other triplet repeat disorders?
Gain of function mutation
CGG triplet in an UTR is what mutation?
GAA triplet in an intron is what mutation?
CAG triplet in an extron is what mutation?
Fragile X syndrome involves what gene?
Why is the disease called Fragile X syndrome?
the triple repeats give the X chromosome a “broken” appearance on G banding
How does Fragile X rate in terms of mental retardation diseases?
Second behind Downs
Characteristic phenotype of Fragile X? (3)
1. Long face with large mandible,
2. large, everted ears,
3. macroorchidism in 90% of post-pubertal males
What phenotype of a disease is similar to Fragile X's?
Fragile site is seen where on the chromosome?
At the fragile site, what is found?
CGG is the trinucleotide repeat
Normal CGC repeat at the fragile site?
29 or less
Premutation CGC repeat at fragile site?