Gene Interaction II Flashcards
How much DNA do mitochondria contain?
16.5 kb chromosomes
Most cells have more than 1000 mtDNA molecules and mature oocytes have more than 100k copies of mtDNA
How many genes do mitochondria have and what do they consist of?
37 genes:
13 encode polypeptides
2 rRNAs
22 tRNAs
What kind of changes in mtDNA can result in human disease?
Different rearrangements and point mutations.
How are mitochondrial diseases inherited?
They have distinctive patterns of inheritance due to 3 unusual features of mitochondria:
Replicative segregation
Homoplasmy and heteroplasmy
Maternal inheritance
What is replicative segregation?
Mitochondria copy their genome and then it goes anywhere randomly segregating into new cells.
What is homoplasmy?
All mitochondria have same genome in the cell
What is heteroplasmy?
Different mitochondria within the cell.
Are all mitochondria maternally inherited?
There are exceptions but this is generally the case. (sometimes paternal mitochondria enters egg and somehow the mtDNA gets expressed)
How does replicative segregation contribute to disease?
Mutant mitochondria can clonally expand and pass a threshold for phenotypic expression.
If a mother has a mitochondrial trait and one of her children doesn’t express the trait what are possible causes of this?
Incomplete penetrance
Variable expressivity
What is incomplete penetrance?
Proportion of individuals with a mutation that develop the phenotype.(Fully penetrant diseases are expressed in 100% of the case like huntington’s)
Number of people with the disease/number of people with the mutation
What is variable expressivity?
The degree to which a phenotype is expressed.
What affects expressivity of a gene?
Thought to be affected by additional genetic and environmental factors.
What is an epistasis?
Form of interaction between nonallelic genes in which one combination of such genes has a dominant effect over other combinations.
Which gene is considered the epistatic gene in epistasis?
Gene that does the masking
