The Genetic Basis of Complex Inheritance - Non-Mendelian Inheritance Flashcards
What are the three laws of Mendelian Inheritance?
The Law of Dominance.
The Law of Segregation.
The Law of Independent Assortment.
What is Non-mendelian Inheritance?
Does not fit in with Mendelian’s Law
e.g.
Gene conversion. Intermediate phenotype
Genetic material from only one parent?
What is the mechanism for the following Inheritance patterns : Incomplete Penetrance
Genomic Imprinting
Extranuclear Inheritance
Anticipation
Environmental factor
Genetic Modifiers
Variants from parents
e.g. Mitochondria mutations
e.g. Triplet repeat expansion
What is penetrance?
Penetrance is the frequency with which a trait is manifested by individuals carrying the gene.
Compares risk of the same disease between different mutations
What else apart from the CTFR mutation is responsible for the severity of CF in organs?
Genetic modifiers : Genes that have small quantitative effects on the level of expression of another gene.
May involve polymorphism.
Environment factors:
Lifestyle, Diet, Smoke, Alcohol, Drug,
Stress, Air pollution, Chemicals,
Infection, etc.
What are the effects of CF?
Sinusitis
Lungs - Sticky mucus build up, bacterial infection and widened airways
Skin - sweat glands produce salty sweat
Liver - blocked biliary ducts
Pancreas - Blocked pancreatic ducts
Intestines - Cannot fully absorb nutrients
Reproductive organs - complications
What is responsible for the rapid increase in prevalence of diabetes in the pacific region
Not merely genetic factors
obesity, unhealthy diets, and physical inactivity are also responsible
What is genomic imprinting?
When genes are altered / shut off during the production of gametes
What is Bi-allelic?
Same allele is turned on in both chromosomes from each parent?
What is mono-allelic?
Gene is only turned on from one of the parents chromosomes
What is the expression of genetic disease like in imprinted DNA?
Higher because there is only only copy of the gene
What are Epigenetic modifications?
Heritable changes in gene function that cannot be explained by changes in DNA sequences
What is Uniparental disomy?
Inheritance of a chromosome pair from one parental origin, because genes can be turned off there is a high risk of genetic mutation?
What are the three sources of UPD?
Trisomy rescue, Monosomy rescue, Mitotic error (non-disjunction or Duplication)
What is the result of uniparental diploidy?
Gynogenic
- 2 maternal genomes
- Mass of embryo
- Ovarian teratoma
Androgenic
- 2 paternal genomes
- Mass of placenta
- Hydatidiform mole
What is responsible for Angelman UPD?
Paternal UPD
What is responsible for Prader - Willi syndrome?
Maternal UPD
Describe the DNA of mitochondria
Circular form
Lack of efficient DNA repair system.
Lack of protective proteins, such as histones.
Damaged by reactive oxygen species (ROS), such as free radicals.
Describe the incidence of mutations of Mitochondria
100-fold higher than the nuclear genome.
What is polyploidy?
up to thousands mitochondria per cell.
2 - 10 copies per mitochondrion.
What is Homoplasmy?
A eukaryotic cell whose copies of mitochondrial DNA are all identical. When in normal and healthy tissues, all cells are homoplasmic.
What is Heteroplasmy?
(two or more mtDNA)
What does mitochondrial Disease affect?
Tissues with high metabolic demand
What is a three parent baby?
Nucleasr DNA from one woman, plus the mitochondrial DNA from another woman, plus the fertilisation by a male
What are triplet repeat diseases?
Diseases whereby a triplet repeat is repeated moreso than normal, Hungtington’s disease
Define anticipation
Anticipation:
Disease presents at earlier age and/or increasing severity in succeeding generations
Give examples of diseases that are spotted in earlier generations and increase with severity in later ones
Hungtington’s disease
Myotonic dystrophy
Fragile X syndrome
What is the source of mitochondrial disease?
Form of maternal inheritance - mitochondrial DNA comes from the mother
What type of disorder is cystic fibrosis?
Autosomal recessive disorder
Caused by faulty 7q31 gene
How does the affected CTFR gene result in the condition?
Chloride channel responsible for removing chlorine from the cell is absent
Sticky mucus build up on the outside of the cell because this protein is absent
Describe the disorder of Myotonic dystrophy
Autosomal dominant disorder
What is the effect of
Severe distal muscle weakness and learning disabilities
Age of onset decreases with successive generations
Describe the disorder of duchenne’s muscular dystrophy
X-linked recessive
Where is the mutation in duchennes musculr dystrophy?
In the dystrophin gene
What is the effect of duchennes muscular dystrophy?
Weakness of proximal muscle (close to the trunk of the body)
Delay in walking
Death at around 20 years
What are the three mechanisms for epigenetic modifications?
DNA methylation, histone modification and non-coding RNA (ncRNA)-associated gene silencing
Why can’t the other copy of the gene compensate in the case of uniparental diploidy?
The same gene on the other chromosome can not compensate for the deletion because it has been turned off by methylation, an epigenetic modification.
