Mendelian Inheritance / Pop. Genetics - Dr. Taylor L2

Question 0

What are the four basic patterns of single-gene inheritance? (genes located in the nucleus)

Answer 0

1. Dominant autosomal / pseudoautosomal
2. Dominant X-linked
3. Recessive autosomal / pseudoautosomal
4. Recessive X-linked

Question 1

What is a pseudoautosomal locus?

Answer 1

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

Question 2

Genes not located in the nucleus?

Answer 2

mitochondrial

Question 3

Define loss-of-function mutation

Answer 3

mutation that reduces or eliminates the function of a gene product

Question 4

Define co-dominant gene and give an example

Answer 4

two different alleles of a locus are expressed

ABO blood typing

Question 5

Define incompletely dominant

Answer 5

homozygotes more severely affected than heterozygotes
or
heterozygote phenotype is somewhere in between the two homozygotes

Question 6

Penetrance vs. Expressivity of a gene?

Answer 6

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

Question 7

Define age-dependent penetrance and the example given in the text.

Answer 7

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.

Question 8

Congenital versus Genetic disease

Answer 8

Congenital is any disease present at birth

Genetic is any disease caused by a gene mutation

Question 9

Give some factors that obscure the (Mendelian) inheritance pattern in a pedigree.

Answer 9

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

Question 10

Define genetic heterogeniety

Answer 10

Different mutations at the same locus (allelic heterogeneity) or
Mutations at different loci (locus heterogeneity) or
Both
All leading to the same disorder (i.e. not a really a single gene mutation)

Question 11

Define pleiotropy (this is a tough one… ;)

Answer 11

When a gene affects more than one organ system; causes multiple diverse symptoms

Question 12

What is the gene mutated in Wilson’s disease and give a few “classic” symptoms.

Answer 12

gene: ATP7B helps transfer excess copper into the blood stream and bile
symptoms: cirrhosis of the liver, neurological (psych. & movement disorder), Kayser-Fleischer rings

Question 13

Describe the Mitochondrial Inheritance pattern.

Answer 13

1. Matrilineal Inheritance pattern (non-Mendelian)
2. Homoplasmy and Heteroplasmy
3. Replicative Segregation

Question 14

Distinguish between homoplasmy and heteroplasmy.

Answer 14

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

Question 15

What is a modifier gene?

Answer 15

Genetic factor outside the disease-causing locus that still affects the expression of the Mendelian disease.

Question 16

What is a phenocopy?

Answer 16

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

Question 17

What are stochastic effects?

Answer 17

Randomness giving rise to disease.

Question 18

What is acute intermittent porphyria?

Answer 18

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.

Question 19

Sex Influence and Sex Limitation of genetic diseases?

Answer 19

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