Modes of Inheritance Flashcards
What is penetrance?
The likelihood of having a disease if you have a gene mutation.
What is the difference between Mendelian and non-Mendelian inheritance?
Mendelian inheritance is caused by alteration in DNA sequences, the manner predicted by Mendel’s law.
Non-Mendelian inheritance is the epigenetic modification of DNA.
What is the Common Disease Common Variant Hypothesis?
A graph that shows he disease penetrance vs the allele frequency.
Describe autosomal dominant disorders.
Has 100% penetrance, only need 1 abnormal allele to be affected e.g. Achondroplasia and Huntington’s disease
Describe autosomal recessive disorders.
Need 2 copies to be affected, 1 in 4 risk for child, e.g. Cystic fibrosis
Describe X-linked disorders.
Y chromosome is irrelevant, female carriers can be affected due to X inactivation, e.g. Haemophilia and Dystrophin
Name 3 types of non-Mendelian inheritance.
- Imprinting
- Mitochondrial inheritance
- Methylation
Describe Methylation:
- genes being switched on and off
- occurs on cytosine before a guanine base
- Leads to modification of histones and this represses transcription
- methylation prevents transcription by preventing the binding of polymerase
- Abnormalities cause genetic disease and gene silencing in cancer
- Methylcytosine can mutate very easily into thymine
- Allows your environment to affect your genome
Describe Methylation.
- genes being switched on and off
- occurs on cytosine before a guanine base
- Leads to modification of histones and this represses transcription
- methylation prevents transcription by preventing the binding of polymerase
- Abnormalities cause genetic disease and gene silencing in cancer
- Methylcytosine can mutate very easily into thymine
- Allows your environment to affect your genome
Describe imprinting.
- Controlled by methylation
- Differences in gene expression depending on whether the gene is inherited maternally or paternally
- Specific chromosomal regions contain both maternally and paternally imprinted genes
(-Angelman syndrome (neuro genetic disorder) is caused by imprinting- need working copy of gene from mother (father’s gene is methylated), however mothers is not passed down (uniparental disomy) therefore have 2 of father’s methylated genes.
Can also happen if there is deletion of mothers 15 chromosome)
Describe mitochondrial inheritance.
- Can find DNA in mitochondria
- Many copies in cell
- Important genes for mitochondrial metabolic pathways and ribosomal RNAs
- Inherited almost exclusively maternally
- Point mutations and deletions can occur
(Heteroplasmy- disease that different cells have different proportions of mutant mitochondria, the severity and nature is dependent on the type of mutation, amount of mutant mitochondria overall and the amount of mutant mitochondria in each tissue. Symptoms include diabetes, deafness, myopathy, optic atrophy etc. all dependent. Difficult to test or predict disease and is rare. Male and female affected equally.)
What is a multifactorial disease?
Diseases caused by genetic and environmental factors
Is the penetrance for a multifactorial disease normally high or low?
Low.
Are Mendelian disorders normally of high or low penetrance?
High.
What does a genome wide association study do?
Identify genetic variants that are associated with common disease.
