Lecture 12 - Genetics Flashcards
What are the basic units of the body?
Cells
Where are chromosomes located in the cell?
in the nucleus
genes reside on what?
chromosomes
Genes carry the code for _____
proteins
the genetic code consists of 4 letters, what are the letters and names?
AdenineCytosineGuanineThymine
the nucleus of each human cell contains strands of DNA known as __________ and they are arranged in _____
chromosomes and they are arranged in pairs
There are 22 pairs of ____ chromosomes and one pair of ____ chromosomes
22 pairs of autosomal chromosomes and one pair of sex chromosome
Each chromosome consists of a series of genes, and the Human Genome Project has identified about how many protein-coding genes?
19,000
Each gene contains the genetic information required to produce a ____.
protein
Each ____ is made specifically to perform a necessary body function
protein
Mutations of a certain gene locus may affect one or both of the ______ in a pair
chromosomes
What does it mean to be heterozygous for a disorder?
when one chromosome in the pair is affected
what does it mean to be homozygous for a disorder?
if both chromosomes at a given gene locus are affected
what is the definition of mutation>
permanent change in the DNA
when a mutation affects germ cells, it can be transmitted to _____
progeny
when a mutation affects a somatic cell it can result in what two things?
tumors or developmental malformations
What are the names of the three types of mutations?
point (missence) mutationframeshift mutationtrinucleotide repeat mutation
what is the definitions of a point (missence) mutation and what is an example?
single nucleotide base substitutedExamp: sickle cell anemia
What is the definition of a frameshift mutation?
insertion or deletion of one or two base pairs, altering reading frame of the DNA strand
what is the definition and what is an example of trinucleotide repeat mutation?
amplification of sequence of 3 nucleotidesExamp: Fragile X syndrome
what is a single nucleotide polymorphism?
variation in just one nucleotide (for example, A or T) at a single site on the DNA molecule
over 6 million polymorphisms have been identified, but most are within which three regions?
exonsintronsand intergenic regions
polymorphisms may be markers for multigenic complex diseases, such as what?
diabetes or hypertension
what are different numbers of large contiguous stretches of DNA, from 1,000 to million of base pairs?
copy number variations
in copy number variations how many involve gene-coding sequences, and this may account for variation in what?
half involve gene-coding sequences, and it may account for much PHENOTYPIC variation
what refers to modulation of gene expression without altered DNA sequence?
epigenetic changes
epigenetic changes are important in what?
development as well as normal homeostasis
with epigenetic changes, methylation of promoter regions makes them inaccessible to RNA polymerase, thus reducing what?
protein synthesis
what is the definition of alterations in non-coding RNAs?
micro-RNAs (miRNA’s) inhibit translation of their target messenger RNAs into their corresponding proteins
mendelian disorders are diseases caused by what?
single gene defects
what is the definition of autosomal dominant disorders?
implies that the altered gene locus is on an autosome and disease will be evident clinically when only one of the chromosomes i the pair exhibit a mutation at the affected gene locus
the majority of autosomal dominant disorders create which type of changes?
outward physical changes
when is the mutant gene present in autosomal dominant disorders and what is an example?
it is present from birthexample: Huntington disease
(T/F) 1. Many Autosomal dominant disorders are exhibited at birth2. In autosomal dominant disorders the mutant gene is present from birth.
- False - many autosomal dominant disorders exhibits a delayed age of onset2. True
With autosomal dominant disorders, how many parents are usually affected?
one of he parents is usually affected
(T/F) only females can have the disorder and transmit the mutant gene
False - both males and females can have he disorder and transmit the mutant gene
what percent of the offspring will have the disease if only one parent is affected with autosomal dominant diseases?
half or 50% of the offspring will have the disease
what is the definition of reduced or incomplete penetrance?
person has a mutant gene but does not express it phenotypically
what is the definition of variable expressivity?
trait is seen phenotypically in the individuals having the mutant gene but is EXPRESSED DIFFERENTLY among individuals
what is the definition of de novo mutation?
affected individuals may not have affected parents because their disease arose from a new mutation
what is the definition of autosomal recessive disorders?
recessive implies that the trait is expressed only if both genes at a given locus are affected (homozygous individuals)
what is the largest group of mendelian disorder?
autosomal recessive disorders
with autosomal recessive disorders do the parents of the affected individual show the disease?
the parents of the affected individual usually do not show the disease
offspring of heterozygous carrier parents have what chance of getting the disease
offspring of heterozygous carrier parents have a one in four chance of the disease
offspring of heterozygous carrier parent have what chance of being a carrier?
one and two chance of being a carried
if the mutant gene is rare, there is a strong probability that the affected child (proband) is the product of what kind of relationship?
consanguineous this means - relating to or denoting people descended from the same ancestor.
what are the basic concepts of autosomal recessive disorders?
-two germline mutations (one from each parent)-equally transmitted by men and women- 25% of offspring; horizontal pattern in family
what type of pattern is seen in families with autosomal recessive disorders?
horizontal pattern in family
with autosomal recessive disorders - many of these disorders present with enzyme defects that produce what?
inborn error of metabolism
in heterozygous individuals with autosomal recessive disorders, the disease is not clinically event but they may possess reduced amount of what?
the normal enzymecarriers are heterozygous individuals (the disease is not evident clinically)
in autosomal recessive disorders the age of onset is more frequently when?
in early life
the expression of the defect tends to be more ____ and _____ _____ is common
tends to be more uniform and complete penetrance is common
although new mutations do occur, they are usually not detected for what reasons?
since that individual would be a carrier without clinical manifestations
almost all X-linked disorders are recessive or dominant?
recessive
are males or females carried for X linked disorders?
females - because they are usually heterozygous for the gene because they have 2 X chromosomes
who is affected by x linked recessive disorders?
homozygous females and males (who are automatically hemizygous because they have only 1 X chromosome) are affected -mutant genes are on the X (sex) chromosome- women must inherit 2 mutated copies to be affected - all men who inherit the mutation are affected (only one X chromosome)
although it is rare, heterozygous females may demonstrate full expression due to what?
unfavorable lyonization
what is lyonization?
- 16 days after concpetion, all but one X chromosome is randomly inactivated in all of the cells within the zygote’’- Either the maternal or paternal X may be inactivated in each cell and that X remains inactivated in the progeny of the cell
with lyonization, the cells in normal females represent a mixture of two cell types, what are they?
those with active paternal X and those with active maternal X- in disorders of the X chromosome, typically females are an even mixture of normal and abnormal chromosomes
what is unfavorable lyonization?
inactivation of an abnormally high percentage of normal X chromosomes, leading to clinical evidence of the disease in a heterozygote
what is affected in x linked dominant and what is an example?
heterozygoushomozygoushemizygous are all affectedExample: Oral-Facial-Digital syndrome (OFD) type I
What are 2 diseases that are caused by mutations in structural proteins?
Marfan syndromeEhlers-Danlos Syndrome
what is Marfan syndrome?
-Autosomal dominant disorder of connective tissue due to mutation of the FBN1 gene, resulting in abnormal FIBRILLIN, a glycoprotein necessary for normal elastic fiber production
what is the prevalence of Marfan syndrome?
1 in 5,000
what are some clinical manifestations of Marfan syndrome?
tall, thin body habitus with abnormally long legs, arms and fingers (arachnodactyly - spider fingers)-Dislocation of lens of the eye-Aortic aneurysm and dissection leading to heart failure and aortic rupture
Examples: Abraham lincoln? sudden death of basketball players?
What are some clinical manifestations of Ehlers-Danlos Syndrome?
Hyperextensible skin and hypermobile joints
Skin fragility and delayed wound healing
Rupture of colon, large arteries
Hernias
How many different types of Ehlers-Danlos syndrome exist
6 different types
Probably because tis is a problem of collagen synthesis, and there are about 30 different types of collagen
what is the frequency of familial hypercholesterolemia?
1 in 500 in the population
Familial Hypercholesterolemia has a mutation in the gene for what receptor
mutation in the gene for the LDL (low density lipoprotein) receptor (over 900 different mutations have been identified)
Familial hypercholesterolemia shows what changes that are not shown clinically?
impaired metabolism and increased LDL cholesterol in the plasma
*This causes xanthomas of the skin and premature atherosclerosis
if you are heterozygous for familial hypercholesterolemia how many times increased is your cholesterol level?
2-3 X increased cholesterol levels
if you are homozygous for familial hypercholesterolemia how many times increased if your cholesterol level?
homozygous - 5X normal levels
Homozygotes of familial hypercholesterolemia usually die of what before 20 years of age?
MI (myocardial infarction)
What class of drugs has been helpful for controlling cholesterol levels in people who have familial hypercholesterolemia?
the statins
*Role of LDL receptors
What are the two diseases caused by mutations in enzyme proteins ?
phenylketonuria and lysosomal storage diseases
what is phenylketonuria?
autosomal recessive disoder
- severe lack of phenylalanine hydroxylase, leading to hyperphenylalaninemia and PKU
- affected infans are normal at birth but the elevated phenylalanine levels impair brain development, and mental retardation is evident by 6 months of age
phenylketonuria affects about what ratio of caucasian infants?
1 in 10,000 caucasian infants
what disease requires mandatory screening in US newborns?
phenlketonuria
in phenylketonuria, restriction of intake of what will prevent mental retardation?
dietary phenyalanine
what is lysosomal storage disease?
- autosomal recessive transmission
- Commonly affect infants and young children
- Accumulation of insoluble large molecules (sphingolipids and mucopolysaccarides) in macrophages with hepatosplenomegaly
- Frequent CNS involvement, mental retardation and/or early death
what are examples of lysosomal storage diseases?
Tay-Sachs disease
Niemann-Pick disease
Gaucher disease
Mucopolysaccharidoses
Disorders with multifactoria inheritance have many physiologic traits (height, weight, blood pressure, hair color) and may underlie common diseases such as what?
diabetes hypertension gout schizophrenia bipolar disorder
In regards to disorders with multifactorial inheritance, ___ or more genes are responsible plue what other influences?
two or more genes responsible, plus environmental, nongenetic influences
in disorders with multifactorial inheritance, the frequency of inheritance ranges from what percentage?
2-7%
what are the types of cytogenetic disorders
- the normal karyotype
- numeric abnormalties
- structural abnormalties
what is the name for the representation of human chromosome strands that can be stained, photographed and arranged in pair
karyotype
the normal karyotype contains how many pairs of chromosomes?
23 pairs; 22 pair of autosomes and 1 pair of sex chromosomes
XX (females)
XY (males)
So the normal chromosome count is 46
*Genetic disorders arise through alteration of either the autosomes or the sex chromosomes
how many newborns have a chromosomal abnormality?
1 in 200 newborns
What percent of 1st trimester spontaneous abortion does the fetus have a chromosome abnormality?
50% of 1st trimester spontaneous abortions, the fetus has a chromosomal abnormality
what is the definition of euploid?
a normal chromosome count
2 X 23 = 46
what is polyploidy and results in what?
an increased chromosome count that is a multiple of that normally seen
3 X 23 or 4 X 23
What does polyploidy generally result in?
spontaneous abortion
what is aneuploidy? and what are examples?
any number that is not an exact multiple of the chromosome count
Examples:
trisomy (an extra chromosome - 47)
monosomy (absence of a chromosome - 45)
structural abnormalities usually result from what?
chromosome breakage followed by loss or rearrangement of material
what is the definition of translocation?
transfer of a part of one chromosome to another nonhomologous chromosome
- usually fragments are exchanged between two chromosomes (reciprocal translocation)
what is the definition of deletion in regard to structural abnormalities?
loss of a portion of a chromosome
What is the definition of inversion?
when a chromosome breaks in two points, then the released fragment is reunited after a complete turnaround
what is a cytogenetic disorder involving autosomes?
trisomy 21 (Down Syndrome)
what is the most common of the chromosomal disorders?
trisomy 21 (Down syndrome)
What is a risk factor for down syndrome?
increased maternal age
less than 20 - 1 : 1550
greater than 45 - 1 : 25
what is the cause of trisomy 21 (Down syndrome)
due to meiotic non-disjunction of chromosome 21 during formation of the ovum
What are clinical signs of trisomy 21?
mental retardation epicanthis folds flat facial profile cardiac malformations increased susceptibility to infection (including severe periodontal disease in children) large tongue increased prevalence of acute leukemia
what are some examples of cytogenetic disorders involving sex chromosomes?
Klinefelter syndrome
turner syndrome
what is klinefelter syndrome?
male hypogonadism hat develops when there are at least two X chromosomes and one or more Y chromosome
What are some clinical and dental symtoms of klinefelter syndrome?
increased length of lower limbs
reduced body hair
gynecomastia
*Most common reason for hypogonadism
Dentally - increased frequency of taurodontism
what is Turner Syndrome?
Due to partial or complete absence of one of the X chromosomes
what are the clinical manifestations of turner syndrome?
short stature webbing of the neck low posterior hairline shield-like chest high arched palate variety of congenital cardiovascular malformations failure to develop secondary sex characteristics primary amenorrhea
what is the definition of fluorescence in situ hybridization (FISH)
use fluorescent dye-labeled probes that recognize sequences specific to chromosomal regions
what is the definition of comparative genomic hybridization?
Uses different colored dyes arrached to large segments of the test DNA and normal DNA, followed by hybridization
-The amount of each DNA sample are assessed based on the color of the hybridized product, and gene amplification or deletion can be identified
What are the steps in molecular diagnosis of genetic disorders?
- PCR analysis - amplify the DNA in question, then:
- Compare the order of nucleotides of this DNA to a normal DNA sequence
- Use restriction enzymes and run the segments on gel electrophoresis, compare to normal DNA
- Use fluorescently labeled (different colors) nucleotides that are complementary to either the wild type (normal) or mutant sequence, then continue the PCR, determining which nucleotide is incorporated during primer extension
what are the prenatal indications for genetic analysis?
- Mother’s age >34 years
- Parent who is a carrier of a chromosome translocation
- History of previous child with chromosomal abnormality
- Parent who is a carried of an X-linked disorder
what are the postnatal indications for genetic analysis?
- Multiple congenital anomalies
- Unexplained mental retardation and/or developmental delay
- Suspected aneuploidy (eg. Down Syndrome)
- Suspected sex chromosomal abnormality
- Infertility
- Multiple spontaneous abortions
