Advanced Mendelian Genetics Flashcards
What is a dominant allele?
A variant of the DNA of a certain gene that produces an effect on the phenotype when present in either one or two copies
What is a recessive allele?
A variant of the DNA of a certain gene that produces an effect only when there is no dominant allele present
What happens to the production of enzymes compared to the number of mutant alleles present?
- Two wild type alleles: -Normal enzyme level so normal phenotype
- One Wild type allele & One mutant allele that encodes non-functional protein: -Half the normal amount of enzyme but normal phenotype still expressed
- Two mutant alleles encoding non-functional enzyme: -No enzyme produced so mutant phenotype expressed
What is haploinsufficiency?
The presence of half the normal amount of a protein from one functional allele is not enough to give the normal phenotype
How does haploinsufficiency affect the phenotype expressed?
Same as without insufficiency apart from when there is only one wild type and one mutant type present which leads to production of mutant phenotype despite there being half the normal protein present
What is Rubinstein-Taybi syndrome?
Results from a mutation in the gene encoding CBP
CBP plays a key role in promoting transcription of many human genes
The effect is a dominant effect because inheriting one allele encoding non-functional CBP results in disease
What are dominant negative alleles?
Alleles that result from mutations that prevent the actions of a protein and cause the mutant protein to inhibit the action of non-mutant molecules of the same protein inside cells
What happens to the phenotype when a dominant negative allele is present?
Same ad before for homozygous genes.
For heterozygous, half the normal protein is made but the effect of this is inhibited and the mutant phenotype is shown
What is osteogenesis imperfecta?
- Brittle bone disease
- Affects type 1 collagen
- Type 1 collagen is encoded by COL1A1 and COL1A2 genes
- least severe disease caused by mutations which affect the quantity of collagen
- Most severe forms caused by mutations that affect the structure of the COL1A1 or COL1A2 proteins, these reduce the Quality of the collagen produced (Dominant negative mutations)
What occurs during epistasis?
Depends on the interactions between genes
The ‘hidden’ gene is hypostatic to the other gene which is ‘epistatic’
How is an agouti mouse’s hair formed?
The agouti gene is turned on after some initial hair growth to produce the yellow colour, then is turned off again for the later stages of hair growth
How does epistasis work?
Epistatic interactions can occur when the genes involved encode enzymes in the same biochemical pathway
What is penetrance?
- The probability that an individual with an appropriate genotype will show a change in phenotype
- May be complete (100%) or incomplete (less than 100%)
What is expressivity?
Degree of phenotypic change produced by a genotype, can be variable
What is Huntington’s disease?
A disease of the mind and body through twitching of the face limbs and trunk, difficulty walking and eating, depression
-no cure
