Genetics (Week 1) Flashcards
Define and describe some common genetic terms
Define Mendelian inheritance
Disorder of a single gene (Autosomal recessive, dominant or X-linked)
Define variable expression
When the same genetic condition affects members of the same family to different extents
Define incomplete penetrance
A mutation is inherited but the disease does not develop at all
Define complete penetrance
A mutation is inherited by an individual and the disease develops to some extent
Describe the term “double homozygous”
When a fault occurs in two separate genes meaning an individual is a carrier of two different conditions
Define the term consanguinity
This occurs when a mother and father are related to each other and is important in autosomal recessive conditions
Define the term “obligate carrier”
These are family members who must be carriers (this can be worked out from the pedigree)
Describe the concept of X inactivation
This occurs in females in utero where some X chromosome are inactivated, meaning females can suffer from X-linked recessive conditions but to a lesser extend than males
Define the term “genetic anticipation”
Moving down the pedigree chart means the condition gets worse and has an earlier onset age due to more and more repeat sequences being passed onto offspring down the generations
Describe the pattern of mitochondrial inheritance in offspring from a mother compared to a father
A father never passes on a mitochondrial condition to offspring whereas all children of an affected mother will inherit the disease to some extent
Define the term “manifesting carrier”
A female carrier who may show symptoms of the disease she carries to some extent
Define the term “heteroplasmy”
A feature of mitochondrial DNA inheritance where a % of DNA is mutant and reaches a threshold to cause disease
Which gene is specifically associated with male breast cancer?
BRCA 2 gene
Which two types of cancer are BRCA 1 and BRCA 2 associated with?
Breast and ovarian cancer
Which two tumour suppressor genes are known to contribute to bowel cancer?
MSH2 and MLH1
A mutation in which gene causes Cowden syndrome?
PTEN gene
Describe Li Fraumeni syndrome
A rare autosomal dominant cancer predisposition syndrome
Name 4 common genes which when mutated cause ovarian cancer
BRCA 1, BRCA 2, MLH1, MSH2
What is Lynch syndrome (HNPCC)?
Autosomal dominant condition causing an increased risk of colon cancer
Name 4 causative genes involved in Lynch syndrome
MLH1, MSH2, MSH6, PMS2
What does to term syndactyly mean?
Fingers and/or toes are joined together
On average, what percentage of genes in common do siblings have?
50% on average
Define “intergenic regions”
Non-coding areas between genes
