MD1

Question 1

Co-dominance

Answer 1

Both alleles contribute to phenotype of the heterozygote

Question 2

Variable expression

Answer 2

Phenotype that varies with the same genotype

Question 3

Incomplete penetrance

Answer 3

Not all individuals with genotype express mutant phenotype

Question 4

Pleiotrophy

Answer 4

One gene contributes to multiple phenotypic effects

Ex: Different mutations in FGFR3 give rise to different forms of dwarfism

Question 5

Imprinting

Answer 5

systematic approach to expression of certain genes (DNA methylation)

Question 6

Anticipation

Answer 6

Increased severity or earlier onset of disease in succeeding generations
-Huntingtons disease
Normal < 26; Intermediate 27-35; Reduced penetrance 36-39; Full penetrance >40

Question 7

Loss of Heterozygosity

Answer 7

If patient inherits or develops a mutation in tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops

Question 8

Dominant negative mutation

Answer 8

Exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning

Question 9

Linkage dysequilibrium

Answer 9

Tendency for certain alleles at 2 linked loci to occur together more often than expected. Measured in a population, not in a family, and often varies in different populations

Question 10

mosaicism

Answer 10

Presence of genetically distinct cell lines in the same individual. Arises from mitotic errors after fertilization

Question 11

Locus Heterogeneity

Answer 11

mutations at different loci can produce similar phenotype

Ex: Prader-Willi syndrome can be due to mutations chromosomes 11,13, or 15
Ex: Cardiomyopathy
EX: CFTR gene

Question 12

Heteroplasmy

Answer 12

presence of both normal and mutated mitochondrial DNA, resulting in variable expression in mitochondrial inherited disease

Question 13

Uniparental disomy

Answer 13

Off spring recieves 2 copies of a chromosome from 1 parent and no copies from the other

Question 14

Why is it important to take a good family history

Answer 14

• for accurate diagnosis
• clarifies pattern of inheritance
• provides information about natural history and variability

Question 15

List the different modes of inheritance

Answer 15

• Multifactorial (complete) inheritance
• Autosomal dominant
• Autosomal recessive
• X-linked
• Y-linked
• Mitochondrial/maternal

Question 16

What is multifactorial inheritance

Answer 16

Abnormal phenotype or abnormality involving more than one gene along with environmental factors
-Example: venous embolism = Age, obesity, family history, dehydration

Question 17

What are characteristics of an Autosomal Dominant Inheritance

Answer 17

• Multiple Generations are affected
• Males and females are equally affected
• Male to Male transmission occurs
• Each offspring of an affected parent has a 50% chance of being affected and 50% chance of being unaffected

Question 18

What is a de novo autosomal dominant mutation

Answer 18

mutation that occur during spermatogenesis and are associated with advanced paternal age

Question 19

What are characteristics of an Autosomal recessive inheritance

Answer 19

• Greatest recurrence among siblings of affected individuals
• Males and Females are equally affected
• Consanguinity may influence likelihood of a specific recessive disease

Question 20

What are characteristics of X-Linked Recessive Inheritance

Answer 20

• Incidence of condition is much higher in FEMALES than males
• All daughters of affected males will be carriers (since males donate X)
• Sons of carrier females have 50% of being affected (since X must come from mother)
• Daughters of carrier females 50% of being affected (since father will always give normal X)

Question 21

What is the difference between sex-linked, sex limited, and sex influenced traits?

Answer 21

Sex Linked = genes on X or Y chromosome
Sex Limited = phenotype only expressed in one sex
Sex Influenced = One sex more likely to have phenotype (male pattern baldness)