Genetics 1 Flashcards
What is a genes locus?
The precise position of the gene on the chromosome
What is an allele?
Alternative forms of a gene
What is a genetic disease?
One caused by a change in the genes.
What do promotor and splice site sequence change mutations cause?
Stop transcription or cause abnormal splicing
What can some missense mutations do?
Make a protein work faster
What is a wild type?
An individual having normal DNA sequences
What is a stop mutation?
Where a premature stop codon is introduced so the rest of the sequence is not transcribed or translated
What is a missense mutation?
Where there is a different base in the DNA sequence (substitution) but it only affects the codon it is in, the codons after the mutation are unaffected.
What is an Insertion mutation?
Where a base is inserted into the DNA sequence, casing all the codons after the point of mutation to be affected
What is a deletion out of frame mutation?
Where a single base is deleted and so all codons after the point of mutation are affected
What is a deletion in frame mutation?
Where a whole codon is deleted but all codons after the mutation stay the same
What is a triple expansion mutation?
Where a codon is repeated
What is mendelian inheritance?
A change in a SINGLE gene sufficient to cause clinical disease
What is non-mendelian inheritance
Everything else including multifactorial diseases (More than one genetic risk factor)
Describe the percentage of DNA shared by 1st, 2nd and 3rd degree relatives
1st - 50%.
2nd - 25%.
3rd - 12.5%
What is autosomal dominant mutations?
A mutation on any chromosome that isn’t a sex chromosome that makes the person affected. (only need one copy of mutation to become affected)
What is allelic heterogeneity?
Where different mutations in the same gene can cause the same disease
What is locus heterogeneity?
Where the same disease may be caused by mutations in one of several genes
Describe features of autosomal dominant mutations
Disease will be seen in every generation however the severity of disease can be variable. Males and females are equally likely to be affected. 50% chance of passing it too offspring
What is autosomal recessive
A mutation where you need both chromosomes to have the mutation to be afffected
Describe some features of autosomal recessive mutations
Often only one generation is affected. 25% chance of passing it onto offspring. Increased likelihood in consanguineous families.
What is an X-linked disease?
A mutation on the X chromosome that causes clinical disease. It is often recessive
Describe features of an X-linked recessive inheritance
For female carriers - Half of male children affected and half of daughters will be carriers.
For affected male - All sons will be normal but all daughters will be carriers
What does nonpenetrance mean?
Failure of a genotype to manifest
Variable expression
Where different family members may show different features of a disorder
Where are nonpenetrance and variable expression seen more often?
In dominant conditions
Describe features of mitochondrial DNA
Contains important genes for mitochondrial metabolic pathways and ribosomal RNA, inherited exclusively maternally and point mutations and deletions can occur
Describe features of mitochondrial inheritance
Diseases in mitochondrial DNA is rare, is is via maternal transmission only and sons and daughters are equally affected.
