Principles Of Genetics Flashcards
What is a proband?
First diagnosed person in the pedigree
Describe autosomal dominant inheritance
Only 1 allele of a gene is needed for expression
Unaffected individuals do not transmit trait
Males and females can transmit to both genders
Trait is expected in every generation
Recurrent risk is 50%
Describe autosomal recessive inheritance
Two copies of mutant allele is needed to influence phenotype
If one mutant allele present the individual is a carrier of the mutation but wont display a phenotype
Females and males affected equally
Describe X linked recessive inheritance
Disease allele on X in males is termed hemizygous
Females can be hetero or homozygous (rarely affected)
Always expressed in male carriers
Unaffected males do not transmit the trait (not carriers)
Female carriers transmit to 50% of sons and 50% of daughters
All daughters of affected males are heterozygous carriers
Never father to son transmission
Ex. Duchenne’s
Describe mitochondrial inheritance
All offspring of an affected woman will be affected
Affected males do not pass onto offspring
Severity of disease depends on threshold or load
Describe X linked dominant inheritance
Males with the disease allele transmit the trait only to females (100% transmission to females)
Females with the disease allele transmit the trait to both males and females equally
50% transmission to offspring
What is Leber’s hereditary optic neuropathy (LHON)?
Mitochondrial disorder
Degeneration of retinal ganglion cells
Caused by one of three pathogen mtDNA point mutations affecting NADH dehydrogenase which makes the RGC unable to transmit signals to the brain
Acute or subacute loss of central vision
What is myoclonic epilepsy and ragged red fibers (MERRF)?
Mitochondrial disorder
Caused by mutation in the gene encoding for tRNA lysine which disrupts the synthesis of cytochrome c oxidase
Pts present w/ myoclonus muscle movement, ataxia, seizures and dementia
Large variability of presentation due to heteroplasmy
What is mitochondria encephalopathy, lactic acidosis and stroke like episodes (MELAS)?
Most common maternally inherited mitochondrial disease
Affects many body systems (brain, NS, muscles)
Sx. Stroke, dementia, deafness, cognitive impairment, DM, short stature and migraines
What is euploidy?
Cells with a normal number of chromosomes
What is nondisjunction?
Abnormal separation of one or more pairs of homologous chromosomes or sister chromatids
Germline mutation if occurs during meiosis
If occurs during mitosis person will exhibit mosaicism
What is polyploidy?
Cells contain a complete set of extra chromosomes in the cells
Multiple of 23 is compatible with life
What is aneuploidy?
Cells contain a missing or additional individual chromosome
Ex. Monosomy, trisomy
What is uniparental disomy (UPD)?
Both chromosomes are inherited from one parent
What is Prader Willi syndrome?
Paternal chromosome 15 deleted and mothers is imprinted/turned off
Short stature, hypotonia, small hands/feet, obesity, mild to moderate intellectual disability and uncontrolled eating
Ex of UPD