Flashcards in Mendelian Inheritance / Pop. Genetics - Dr. Taylor L2 Deck (20):
What is a pseudoautosomal locus?
locus located on the X chromosome that does not show X-linked inheritance pattern because it _can_ recombine with counterparts on the Y chromosome
occurs in male meiosis
What are the four basic patterns of single-gene inheritance? (genes located in the nucleus)
1. Dominant autosomal / pseudoautosomal
2. Dominant X-linked
3. Recessive autosomal / pseudoautosomal
4. Recessive X-linked
Genes not located in the nucleus?
Define loss-of-function mutation
mutation that reduces or eliminates the function of a gene product
Define co-dominant gene and give an example
two different alleles of a locus are expressed
ABO blood typing
Define incompletely dominant
homozygotes more severely affected than heterozygotes
heterozygote phenotype is somewhere in between the two homozygotes
Penetrance vs. Expressivity of a gene?
Penetrance: the probability that a gene will have a phenotypic expression (of _any_ severity)
Expressivity: the severity of expression of a phenotype among individuals with the same disease-causing genotype
Define age-dependent penetrance and the example given in the text.
Occurs when phenotype expression (all-or-none) varies with age.
Ex: Neurofibromatosis. Penetrance in newborns is <50%. Penetrance in adults is 100% Symptoms develop slowly throughout childhood.
Congenital versus Genetic disease
Congenital is any disease present at birth
Genetic is any disease caused by a gene mutation
Give some factors that obscure the (Mendelian) inheritance pattern in a pedigree.
Affected individuals not suriving to birth
Accuracy of information
Define genetic heterogeniety
Different mutations at the same locus (allelic heterogeneity) or
Mutations at different loci (locus heterogeneity) or
All leading to the same disorder (i.e. not a really a single gene mutation)
Define pleiotropy (this is a tough one... ;)
When a gene affects more than one organ system; causes multiple diverse symptoms
What is the gene mutated in Wilson's disease and give a few "classic" symptoms.
gene: ATP7B helps transfer excess copper into the blood stream and bile
symptoms: cirrhosis of the liver, neurological (psych. & movement disorder), Kayser-Fleischer rings
Describe the Mitochondrial Inheritance pattern.
1. Matrilineal Inheritance pattern (non-Mendelian)
2. Homoplasmy and Heteroplasmy
3. Replicative Segregation
Distinguish between homoplasmy and heteroplasmy.
1. homoplasmic female will pass it on to ALL her children; equal severity of disease among offspring
2. heteroplasmic female will pass it on to ALL her children; the fraction of mutant mitochondria (and thus severity/symptoms) in offspring will vary
What is a modifier gene?
Genetic factor outside the disease-causing locus that still affects the expression of the Mendelian disease.
What is a phenocopy?
Disease due to non-genetic factor. e.g. environment or other factors cause a mutation which in turn causes a disease.
ex: radiation exposure --> thyroid cancer
What are stochastic effects?
Randomness giving rise to disease.
What is acute intermittent porphyria?
Genetic disease that manifests in response to "exposures"
In the heme production pathway, a deficiency of porphobillinogen deaminase (enzyme) causes pathway to stall and a buildup of porphobilinogen (intermediate) in the cytoplasm.