WEEK 3 Flashcards
What does the term “gene interaction” mean?
It is used to express the idea that multiple genes interact to express a certain phenotype
What are two examples of Pleiotropy?
Marfan syndrome & Porphyria variegata
Define ‘Pleiotropy’
The phenomenon in which a single gene mutation results in multiple phenotypical abnormalities
Male individuals are said to be __________________
Hemizygotic
this is because males have XY chromosomes therefore they only require one copy of the gene
How can you notice an X-linked recessive gene in a pedigree tree?
- Skipping generation
- Mostly affecting males
- No male to male transmission (e.g father cannot pass on to son)
- Sons of heterozygous mothers have a 50% chance of being affected
- Females usually must be homozygous to be affected
How can you notice an X-linked dominant gene in a pedigree chart?
- Fathers will transmit to all daughters but no sons
- Mothers will transmit to 50% to daughters and sons
- No male to male transmission
- Transmitted through both parents
Define ‘Penetrance’
The percentage of individuals that show at least some degree of expression of a mutant genotype
What is ‘expressivity’?
The range of expression of the mutant genotype
What is ‘imprinting’?
A type of marking process that has a memory and involves DNA Metyhlation (silencing of a gene)
What are two examples of imprinting?
Prader-Willi syndrome & Angelman syndrome
What is Epistasis?
Where the expression of one gene masks or modifies the effect of a second gene
What phenotypic expression can result from Epistasis?
When phenotypic characteristics act in an antagonistic manner, masking occurs. When genes exert their influence on another, complementary/cooperative phenotypes occur.
What is ‘Variable expressivity’?
Patients with the same genotype have varying phenotypes
(e.g varying disease severity)
Define ‘Incomplete penetrance’
Not all individuals with a mutant genotype show the mutant phenotype
% penetrance X probability of inheriting genotype = risk of expressing phenotype
Define ‘genomic imprinting’
An analogous situation in which a segment of DNA is marked and that mark is retained and recognised throughout the life of the organism inheriting the marked DNA
What is Prader-Willi syndrome?
Prader-Willi syndrome occurs when maternally derived genes are silenced and the disease occurs when the paternal allele is deleted or mutated. Chromosome 15 of parental origin is involved.
Symptoms include Hyperphagia (excessive eating), Obesity, Intellectual disability, Hypogonadism (not enough testosterone), Hypotonia (reduced muscle tone)
25% of cases are due to maternal uniparental disomy
POP: Prader-Willi, Obesity/overeating, Parental allele deleted
What is Angelman syndrome?
Occurs when paternally derived UBE3A is silenced and disease occurs when the maternal allele is deleted or mutated. UBE3A on chromosome 15 of maternal origin is involved.
Symptoms include Seizures, Ataxia, severe Intellectual disability, inappropiate Laughter
(set SAIL for angel island)
5% of cases are due to paternal uniparental disomy
(MAMAS: Maternal allele deleted, Angelman syndrome, Mood, Ataxia, Seizures)
