genetic terms Flashcards
codominance
both allese contribute to the phenotype of the heterozygote
examples: blood groups A, B, AB and a1 antitypsin deficiency
Variable expressivity
phenotype varies among individuals with same genotype
-2 patients with NF type 1 may have varying disease severity
incomplete pentrance
not all indivudals with a mutant genotype show the mutant phenotype
BRCA! gene mutations do not always result in breast or ovarian cancer
pleiotripy
one gene contributes to multiple phenotypic effects
-example untreaked phenylketonuria manifasts with light skin, intellectural disability, must body odor
anticipation
increased severety or eralier onset of disease in succeeding generations
loss of heterozygosist
if a patient inherits or develops a mutation in tumor supressor gene, the complementary allele must be deleted/mutated before cancer develops. this is not true for oncogenes
ex retinoblastomia and the two hit hypothesis
dominant negative mutation
exerts a dominant effect
a heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning.
example: mutation in a transciption factor in its allosteric site. the nonfunctioning mutant can still bind dna (binding site), preventing wild type transcription factor from binding
linkage disequilibrium
tendency for certain alleles at 2-linked loci to occur together more often than expected by chance. measured in a population not in a family, and often caries in different populations
mosaicism
presence of genetically distinct cell lines in the same individual.
arises from mitotic errors of fertilization
somatic mosaicism - mutation propagates though multiple tissues or organs
gonadal mosaicism - mutation only in egg or sperm cells
note: mccune-albright syndrom is lethal if the mutation is somatic, but survivable if mosaic
locus heterogeneity
mutations at different loci can produce a smiliar phenotype example albinism
allelic heterogeneity
different mutations in the same locus produces the same phenotype
example B-thalassemia
heteroplasmy
presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrial inherited disease
uniparental disomy
-offspring receives 2 copies of chromosome from 1 parent and no copies from the other parent
heterodisome (heterozygous) indicates meiosis 1 error
isodisome (homozygos ) indicateds a meiosis II error or postzygotic chromosmal duplication of one of a pair of chromosomes and loss of the other original pair
P^2 + 2PQ + q^2 = 1
P + q = 1
P^2 frequency of homozygosity for allele p
q^2= freqency of homozygosit for allele q
2pq = frequency of heterozygosity (carrier in autosomal recessive)
The frequency of x-linked recessive disease in males is q
females is q2
Prade-willi syndrom
- maternal imprinting
- maternal allele is silent, or inactivated
- paternal allele is the active allele
- active allele is muted or deleted –> disease
-hyperphagia, obesitt, intellectual disability, hypogonadism and hypotonia
25% cases due to maternal uniparental disome (two maternal impreinted genes are recieve, no paternal gene received)
