Principles of Genetic Inheritance Flashcards
Mosaicism
Condition in which cells from a patient have different genotypes (& kayotypes)
Down Syndrome
Trisomy 21
46XX
47XX
Klinefelter Syndrome
46XY
47XXY
Turner Syndrome
46XX
45XO
Deletion in chromosome 15
Paternal chromosome deleted = Prader Willi Syndrome
Maternal chromosome deleted = Angelman Syndrome
Beckwith-Wiedemann
Uniparental disomy of Chromosome 11
Autosomal Dominant Inheritance
Only 1 allele of a gene needed for expression
Can transmit trait to both females & males
Trait expected in every generation
Recurrent risk = 50%
Ex. Postaxial polydactyly
Retinoblastoma
Autosomal Recessive Inheritance
2 copies of a gene is needed to influence phenotype
Recurrent risk in heterozygous parents = 25%
Ex. Tyrosine-Negative Albinism
X-linked Recessive
Disease on X in males = hemizygous
Females can be heterozygous or homozygous
Unaffected males don’t transmit the trait
Female carriers transmit disease allele to 50% of sons and 50% to daughters
All daughters of affected males are heterozygous carriers
Ex. Duchenne Muscular Dystrophy
X-linked Dominant
Very rare, no carriers
Males with disease allele transmit trait only to females
Females with disease allele transmit trait to both females and males 50% transmission to offspring
Ex. Hypophosphatemia
- Rickets
- Low serum phospherous
- Vit D metabolism abnormal
Reduced Penetrance
In some cases, 100% of individuals inheriting genetic defect show the clinical presentation (phenotype) of the disease (100% penetrance)
Autosomal dominant inheritance
Phenotype occurs in 90% of individuals inheriting gene defect; 90% penetrance
Ex. Retinoblastoma
Variable Expressivity
Term used to describe the range of phenotypes that vary between individuals with a specific genotype
Ex. Neurofibromatosis
-Cafe-au-lait spots
Locus Heterogeneity
Single disorder, trait, or pattern of train caused by mutations in genes at different chromosomal loci.
Ex. Osteogenesis imperfecta
-Brittle bone disease
Mutation in collagen genes (2 loci; chromosome 7 & 17) either mutation exhibits the same phenotype
Robertsonian Translocation
Relation to down syndrome Long arm (q) of chromosome 21 translocates to the long arm of chromosome 14
Multifactorial Inheritance
Threshold model
Ex. Pyloric stenosis
