Non mendelian inheritance Flashcards
Give mechanism of non mendelian inheritance inheritance pattern and mechanism?
Incomplete Penetrance- Environmental factor and genetic modifiers to specific genetic traits
Genomic Imprinting- Variants from parents
Extranuclear Inheritance- mitochondrial mutations
Anticipation- Triplet repeat expansion
Complex-multi genic risk
What is penetrance?
penetrance is the frequency with which a trait is manifested by individuals carrying the gene
What is cystic fibrosis caused by?
caused by a mutation in CFTR (autosomal recessive)
Describe genetic modifiers?
genes that have small quantitive effects on the level of expression of another gene
may involve polymorphism, maybe intra or extra genic
What is genomic imprinting?
gene expressed from only one chromosome
parent of origin dependent
Describe epigenetic modifications?
Heritable changes in gene function not explained by changes in DNA sequences
What does methylation mean?
methylcystosine( mC) induces the structural adaptation of chromosomal region so as to perpetuate altered activity states- stops it being available for translation
Give genetic mechanisms of imprinting disorders?
Deletions
Point mutations
Imprinting errors
Uniparental disomy
Describe deletions outcome?
deletion of maternal copy of maternally expressed gene- no working copy of it
deletion of paternal copy of maternally expressed gene -no effect
Describe uniparental disomy?
complete chromosome duplicated and therefore get 2 copies of some genes and 0 copies for others.
Describe a gynogenic uniparental diploidy?
- 2 maternal genomes
- Mass of embryo
- Ovarian teratoma
Describe an androgenic uniparental diploidy?
- 2 paternal genomes
- Mass of placenta
- Hydatidiform mole
What is prader willi syndrome caused by?
caused by loss of paternal elements
What is angelman syndrome caused by?
loss of maternal elements
Why do we inherit mitochondria from mother?
few in sperm but degrade and arent used in creation of embryo
Give features of the mitochondrial genome?
High mutation rate: 100-fold higher than the nuclear genome
Lack of efficient DNA repair system.
Lack of protective proteins, such as histones.
Damaged by reactive oxygen species (ROS), such as free radicals.
What is homoplasmy?
all normal copies of mitochondrial genome
What is heteroplasmy?
two or more mtdna with genetic alteration
What do mitochondrial diseases typically affect?
tissues with high metabolic demand
What is anticipation - triplet repeat expansion?
Disease presents at earlier age and/or increasing severity in succeeding generations.
e.g. Triplet repeat diseases
- Huntington’s disease
- Myotonic dystrophy (DM1)
- Fragile X syndrome
Describe multigenic/ complex inheritance?
Complex inheritance involves multiple genes and environmental factors that influence the risk or development of a condition.
Multiple Low Penetrance Variants: These are genetic variants that each contribute a small amount to the risk of a condition, but none by itself causes the disease.
Rare High Penetrance Variants: These are less common genetic variants that, when present, significantly increase the risk of a condition (e.g., certain mutations in many genes causing similar symptoms in schizophrenia).
-environmental factors often significant
What are the common conditions of multigenic/ complex inheritance?
Heart disease
Breast cancer
Autism
