ST2 notes Flashcards
allelic heterogeneity
different mutations of the same gene
locus heterogeneity
same mutation in different genes
Bardet-Biedl syndrome (BBS)
15 loci are responsible for cilia functions making it a pleiotropic disorder as many different body systems are impaired
shows locus heterogeneity
pleiotropy
one genes influences two or more seemingly unrelated phenotypic traits
Sensorineural deafness
same mutation in 28 different genes
autosomal recessive but two different parents can have a normal child if they have different disease genes
normal child will be a double heterozygous as they will have two different mutant genes
shows locus heterogeneity
genomic imprinting
offspring’s gene expression is parent-specific due to inactivation of the opposite parent’s allele
caused by DNA methylation that suppresses transcription resulting in alterations in gene expression
imprinted gene
methylated and inactive in somatic cells
maternal imprinting
maternally derived allele inactivated
paternal imprinting
paternally derived allele inactivated
Prader-Willi syndrome
maternal imprinting
deletion of paternal chromosome 15q11
Angelman syndrome
paternal imprinting
deletion of maternal chromosome 15q11
uniparental disomy
two copies of a chromosome are inherited from one parent and no copies from the other parent
caused by non-disjunction followed by loss of genetic information
heterodisomy
meiosis I non-disjunction
both homologs from one parent
isodisomy
meiosis II non-disjunction
one chromosome is duplicated
modifier gene
gene that alters the expression of a human gene at another locus that in turn causes a genetic disease
epistasis
effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes (modifier genes)
linkage analysis
family-based
makes use of pedigrees for mapping of monogenetic diseases
association analysis
population-based mapping comparing the frequencies of alleles in affected individuals to unaffected controls for complex diseases
haplotype
series of alleles at linked loci that are co-inherited on a single chromosome
recombination frequency (theta)
estimate of genetic distance
theta = 0.5
NR = R
loci very far apart