Exam 4 Flashcards
(426 cards)
Locus
A segment of DNA at a specific location
Alleles
Alternative possible versions of a gene
Wild type
Single prevailing allele, present in the majority of individuals in a population
Variants or mutants
The other versions of alleles that are not wild type
Polymorphic alleles or polymorphisms
Variant alleles are said to show polymorphism which affect disease susceptibility 
Genotype
An entire set of alleles in a genome, or the set of alleles at a specific locus
Phenotype
Observable expression of a genotype as a morphological, clinical, cellular, biochemical, or other trait 
Homozygous and heterozygous
Homozygous: An individuals two alleles are functionally identical at a locus
Heterozygous: two alleles are functionally different add a locus 
Hemizygous
When an individual only has one allele of a gene
Compound heterozygotes
Individuals with two heterogeneous recessive alleles at a particular locus that can cause genetic disease
Pedigree
Graphical representation of the family tree
Kindred
Extended family
Proband vs consultand
The first affected person who is brought to clinical attention
Vs
The person who brings the phenotype to clinical attention 
 Mosaicism
 Phenotype may only be expressed in a subset of cells, typically 50-50
Ex: muscular dystrophy
Pure dominant
When both homozygous and heterozygous shown identical severity of phenotype
Semidominance/ Incomplete dominance
A disease is more severe in homozygotes compared to heterozygotes
Codominance
Two different variant alleles are expressed together
 Penetrance
The probability that a mutant gene will have any phenotypic expression— Anything less than 100% is reduced penetrance
Expressivity
The severity of expression of the phenotype among individuals with the same disease causing phenotype— Usually variable expressivity 
Modifier genes
Segregating variant alleles, distinct from the disease causing genes, can also influence penetrance and variable expressivity 
Neurofibromatosis (NF1)
NF1 is an autosomal dominant disease and is a common disease of the nervous system/eyes
 Always exert some kind of disease phenotype in heterozygotes (100% penetrance) But the severity varies greatly (Variable expressivity due to different mutations) 
Allelic heterogeneity
The occurrence of more than one allele at a locus— ex. Thalassemia
Different mutations at the same gene making it more or less severe
Locus heterogeneity
The association of more than one locus with a clinical phenotype— ex. Thalassemia from a-globin or b-globin

Different genes give the same phenotype
Clinical or phenotypic heterogeneity
The association of more than one phenotype with mutations at a single locus — ex. B-Thalassemia and sickle cell result from the same b-globin gene mutation