Genetics Flashcards
Maternal imprinting
Gene when inherited from mother is silent.
eg. Prader-Willi
ie. Only children of affected fathers are affected.
Paternal imprinting
Gene when inherited from father is silent.
eg. Angelman
ie. Only children from affected mothers are affected.
Somatic mosaicism
Genetically different cell lines within an individual (may or may not involve germ cells).
Germline (gonadal) mosaicism
Mutations for genetically different cell lines in germ cells, can be inherited and cause full phenotype in offspring.
Chimerism
Two or more genetically different cell lines derived from two (or more) zygotes.
X-linked recessive
No male-male transmission.
Males more likely to be affected.
X-linked dominant
Males usually severely affected (usually lethal in pregnancy). Half of females affected.
Mitochondrial mutation
Maternal transmission (only maternal mtDNA inherited). Variable effects in different organs within family.
Uniparental disomy
Duplication of one parent’s chromosome, other parent’s chromosome suppressed.
Causes autosomal recessive disease derived from single parent.
Linkage disequilibrium
Tendency for alleles of genes / genetic markers to be inherited together in non-random fashion.
Genes close in chromosomal position (unlikely to separate in chromosome assortment or cross-over meiosis)
Diseases with triplet repeat instability in maternal transmission
Myotonic dystrophy (DM1) Fragile X (FRAX) Spinocerebellar ataxia (SCA8)
Diseases with triplet repeat instability in paternal transmission
Huntington (HTT) Spinocerebellar ataxia (SCA1, SCA2, SCA7)
45,X
Turner syndrome Short stature Broad chest, wide-spaced nipples Neck webbing Ovarian failure, pubertal delay
47,XXY
Klinefelter syndrome
Primary hypogonadism - most common sex chromosome cause
Tall stature
Small testes
Azoospermia
Psychiatric and autism spectrum disorders
47,XXX
Triple X syndrome Tall Small head Premature ovarian failure Developmental delay
Genetic risk factors in diabetes
Offspring of affected father - T1DM increased risk
Offspring of affected mother - T2DM increased risk
Monogenic inheritance
Phenotype due to inheriting one mutant gene
Digenic inheritance
Phenotype due to mutation in two different genes
Heterozygosity
Two different alleles for the same gene
Allelic heterogeneity
Different mutations at same locus cause similar phenotype
Locus heterogeneity (aka non-allelic heterogeneity)
Mutations in genes at different chromosomal loci cause similar phenotype
Hemizygosity
Only one allele of gene is present
Alpha thalassaemia
Impaired alpha globin chains, relative excess in beta globin chains 1 - Silent carrier 2 - Trait 3 - HbH disease 4 - Hydrops foetalis
Most common cardiac abnormality in Turner’s syndrome
Bicuspid aortic valve
Cause of male infertility in cystic fibrosis
Obstructive azoospermia (Due to bilateral absent vas deferens)
