principles of genetic inheritance Flashcards
Autosomal dominance?
one copy of a dominant mutant allele in one of the autosomes is enough to express the gene
Autosomal recessive?
one mutant allele means the person is a carrier; two mutant alleles means the person will display the condition
X-linked recessive-?
always are expressed in Males since they only have one X chromosome. Females will be carriers unless they possess both recessive alleles (DMD)
X-linked dominant?
when the mutation is on the father’s X chromosome all daughters will express the condition. Father to son X transmission is not possible.
no carriers
Leber’s hereditary optic neuropathy (LHON)
?
Point mutation affecting NADH dehydrogenase
Degeneration of retinal ganglion cells
mitochondrial disorders?
Affected mother will pass on mitochondrial DNA to all children
LHON
MERRF
MELAS
MERRF?
mutation in gene encoding tRNA for lysine
disrupts synthesis of cytochrome c oxidase
MELAS?
Affects many body systems, CNS, and muscles
Stroke & dementia
Lactic acidosis
Single point mutation, can’t use pyruvate
Nondisjunction?
too many or too few chromosomes
Polyploidy?
complete set of extra chromosomes
Aneupolid?
missing or addition individual chromosomes
Uniparetal Disomy?
: two chromosomes inherited from same parent, parent specific imprinting
Genomic Imprinting:?
- one allele is inactive
- silencing thru methylation of 5’ end of gene
Prader Willi syndrome?
Deletion of a region on chromosome 15
Paternal gene imprinted: Prader Willi Syndrome
Short, hypotonia, small hands/feet, obesity, mild to mod intellectual disability
Maternal gene imprinted: Angelman syndrome
Severe intellectual disability, seizures, ataxic gait
Klinefelter syndrome?
47XXY
Varying degrees of cognitive behavior, primary hypogonadism (Low T), small testes, gynecomastia, tall, infertile, can have more chromosomes
Turner Syndrome?
45, XO
infertile, webbed neck, no cognitive defects
Down’s syndrome?
trisomy 21
Most common, increased with maternal age, due to translocations
Cardiac defects, duodenal atresia
Patau Syndrome
trisomy 13
Severe developmental abnormalities, perinatal death within 1 week( <13% survive to 10yo)
CNS, kidney issues, heart
Edwards Syndrome:?
Triomy 18
Abnormal development, perinatal death within 1 year (<10% of live births survive to 10yo)
Microencephaly, small mouth
Uniparental disomy
Individual received two copies of a chromosome or part of a chromosome from one parent and none from them other
Often asymptomatic, unless the only chromosome given has imprinted genes
. Genomic imprinting
certain genes are expressed only from the mother or father.
Imprinted alleles are silenced thtough methylation of 5’ end; gene expressed only from non-imprinted allele
Imprinting is epigenetic, involves methylation and histone mods of egg/sperm cells
chromosomal mutations? what are the 4 types
Inversion
Duplication
Translocation
deletion
karyotyping?
Technique that allows determination of the number, size, and gross structure of metaphase chromosomes
Does not provide information at molecular level
Neurofibramatosis?
variable expressivity, cafe du lait spots, tumor like growths
caused by inactivating mutant of NF-1 gene
retinablastoma?
penetrance, autosomal dominant, genotypes dont match phenotypes often
Microdeletions in chromosome 13 cause defect in RB gene.
In hereditary form: one copy of RB gene is mutated or lost, leading to higher risk of cancer
Good second copy of gene is damaged due to somatic mutation
Cells lose control of G1 checkpoint
Marfan Syndrome?
Affects the connective tissue, subsequently many different systems
variable expressivity
Reduced/ Incomplete Penetrance: ?
Frequency a gene manifests: penetrance
-not all people with genotype will have phenotype
Variable expressivity: ?
- range of phenotypes in patients with specific genotype
- neurofibromatosis/marfan
Locus Heterogeneity:
- trait caused by mutations at genes in different locations
- ”osteogenesis imperfecta” chromosome 7,17
Heteroplasmy
.Presence of more than one type of mitochondrial DNA
Symptoms don’t develop until adulthood because these mutant mitochondrial alleles must undergo many cell divisions before presenting
Polygenic
more than one gene affects phenotype
Multifactorial:
environmental factors affect trait too
-recurrence risk if higher, especially if more than one family member affected
Liability of distribution:
If you pass threshold, you have disease
Pyloric stenosis:?
more common in males
-least affected sex transmits condition more
Postaxial Polydactyly method of inheritance?
autosomal dominant
Tyrosinase-Negative Albinism method of inheritance?
autosomal recessive
Duchenne Muscular Dystrophy method of inheritance?
X-linked Recessive
Hypophosphatemia method of inheritance?
X-linked Dominant
