Flashcards in Exam #5: Single Gene Disorders Deck (37):
1
What are the five functions of proteins that can be impaired in the single-gene disorders?
1) Protein with catalytic activity (Enzymes) - Recessive
2) Proteins involved in transport & storage - Recessive
3) Proteins with structural function
4) Proteins involved in growth, differentiation, & development
5) Receptor & signaling proteins
2
Null Mutation
Destroys a protein
3
Loss of Function Mutation
Reduce protein activity
4
Gain of Function Mutation
Alter protein function and/or convey a new function
5
Dominant Alleles
Produce phenotype in heterozygous state
6
Recessive Alleles
Produce phenotype in homozygous state
7
Carrier
Patient w/ one defective allele but without disease
8
Compound heterozygote
Patient w/ two defective but non-identical alleles leading to disease phenotype
9
What defects generally show recessive inheritance? Why?
1) Enzyme defects
2) Mutations in proteins involved in transport & storage
- One functional allele remains
- Loss can be compensated for by regulatory mechanisms
10
What defects generally show dominant inheritance?
1) Structural protein defects
2) Defects in proteins involved in growth, differentiation & development
3) Defects in receptors & signaling proteins
11
Haploinsufficiency
Half of the gene does is not sufficient for the cell to carry out its function
12
Dominant Negative Effect
- Mutation produces an abnormal protein that may compete with the wildtype form and impair function
- E.g. structural proteins
13
Gain of Function Mutation
- IF mutation produces a protein with a new function, it will have an effect no matter how many wildtype forms of a protein are present
- Signal transduction proteins
14
Lack of Backup
- Cancer development after inactivation of both alleles i.e. the "two hit" model
- E.g. Rb
15
What determines sex in humans?
Presence or absence of Y chromosome
16
Why are X chromosome mutations in men dominant?
They only have one copy of the genes b/c they only have one X chromosome
17
Why are females mosaics for X chromosomes?
One is inactivated early during embryogenesis in a RANDOM but FIXED manner
18
Mitochondrial Gene Defects
DO NOT follow mendelian rules of inheritance
19
Who are mitochondrial defects inherited from?
Mother
20
Why is there variable expression of mitochondrial defects?
Cells have many mitochondria with many copies of the chromosome
21
Consanguineous Mating
Mating of closely related individuals that increases risk for development of recessive disease
22
Coefficient of inbreeding
- Degree of homozygosity of a child
- 1/4 for siblings
- 1/8 for first cousins
23
Autosomal Recessive Pedigree
- Affected children usually have normal parents
- Both sexes are equally affected
- Consanguinity is often present
24
Autosomal Dominant Pedigree
- Affected child has at least one affected parent
- Both sexes are equally affected
- Disease can be transmitted from father to son
25
Incomplete penetrance
Not all people with disease genotype having phenotype
26
Expressivity
How severe a disease phenotype is
27
Neurofibromatosis Type 1
- Complete penetrance
- Variable expressivity
28
Premutation
- Seen in diseases caused by a specific number of repeats
- Individual close to carrying number of repeats for disease phenotype but not yet
- High chance of producing gametes with pathogenic number of repeats
29
Huntington Disease
- Permutation
- Anticipation
30
Anticipation
- Severity of disease phenotype increases when transmitted through a pedigree
- Seen in repeat expansion diseases
31
Fitness
Chance of reproduction
32
Mutation Hotspot
- Chromosomal region where mutations occur frequently
- CG dinucleotide repeat is common example
- Cytosine is methylated to methylcytosine & deaminated, yielding tymine
33
Ova Mutations
Nondisjunction
34
Sperm Mutations
Point Mutation
35
X-linked Recessive Pedigree
- No father-son transmission
- Affected boys usually have unaffected parents
- Males are affected more frequently than girls
36
X-Linked Dominant Pedigree
- Male transmits to all of his daughters
- Female transmits to half of children regardless of sex
37