Mendelian Inheritance / Pop. Genetics - Dr. Taylor L2 Flashcards Preview

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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.

Reduced penetrance
Variable Expressivity
Other genes
Environmental factors
Affected individuals not suriving to birth
Accuracy of information
New mutations


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"
Autosomal Dominant
In the heme production pathway, a deficiency of porphobillinogen deaminase (enzyme) causes pathway to stall and a buildup of porphobilinogen (intermediate) in the cytoplasm.


Sex Influence and Sex Limitation of genetic diseases?

Sex Influence: condition is more common in one sex than the other. ex: gout more common in males

Sex Limitation: only one sex _can_ express a disease. ex: prostate cancer