Lecture 3 Flashcards
(22 cards)
What does wild type mean?
Most common or normal version of a gene, phenotype, etc
What does a wild-type allele produce? What phenotype is this?
-A functional polypeptide
-Wild-type phenotype
What does a recessive amorphic loss of function allele produce? What phenotype is this?
-Produces a non functioning polypeptide
-Severe mutant phenotype
What does a Recessive hypomorphic loss of function allele produce? What phenotype is this?
-Produces a partially functional polypeptide
-Mild mutant phenotype
What does a dominant-negative allele produce? How does this happen? What phenotype is this?
-Produces a polypeptide that interferes with the wild-type polypeptide.
-Competes for binding site
-Severe mutant phenotype
What is a wild type allele?
Produces a working enzyme or protein, or most common genotype/phenotype in population
What is a loss of function allele?
Makes no protein, less protein or a non working protein
Why is wild type allele dominant over loss of function allele? What is this called?
Because producing half the normal amount of protein is usually enough to maintain wildtype phenotype. This is called haplosufficiency
How can dominant alleles be negative regarding gain of function abilities?
DOminant alleles can be gain of function mutations in which the mutant allele produces a protein that has increased detrimental function
How can dominant alleles be negative regarding loss of function alleles? What is this called and give an example.
Dominant alleles can be loss of function allels, where in heterozygote half as much protein is synthesized and this isn’t enough for the normal phenotype, meaning its haploinsufficient. ex. Tailless cat
Where are dominant lethal genes expressed?
In homozygote and heterozygote
Where are recessive lethal genes expressed?
Only expressed in the homozygote
What is penetrance? Give example?
Percentage of individuals with a specific genotype display the expected phenotype. For example, if 42 ppl have alleles for polydactyly but 38 show trait, penetrance is 38/42=90%
What is expressivity? Give example.
Extent or severity of a phenotype. For example, in polydactyly, some individuals have fully functional extra fingers or toes, while others have a small skin tag
Why might incomplete penetrance and variable expressivity occur? Give an example.
-Due to the influence of other genes or environmental factors, which can modify or suppress a genes effect
-For example, a gene makes an enzyme that only functions in a certain temp range, so outside of this range, the ezyme fails to express the phenotype.
What are 3 examples of rare autosomal dominant diseases with variable expressivity?
Split hand foot disease
-Deficiency or absence of one or more central digits of hand or foot
Piebaldism
-Absence of melanocytes in certain areas of skin and hair
Huntingtons disease
-Neurodegenerative disease, causes loss of muscle coordination, cognitive decline and dementia
What 4 factors affect phenotypic expression?
1) Age
2) Sex
3) Temperature
4) Chemicals
What is norm of reaction?
Range of phenotypes a single genotype can produce under different environmental conditions
What does phenocopy mean?
Change in phenotype caused by environmental factors that mimic the effects of a genetic mutation
Give examples of how controlling our environment can influence the appearance of a mutant phenotype or disease.
-Phenylketonuria (PKU) symptoms can be avoided by regulating intake of phenylalanine
-Many inherit genes that predispose them to heart disease, but regulating diet and excercise can affect occurrence (penetrance) and severity (expressivity) of the disease
Why can different combinations of alleles from multiple genes produce various phenotypes?
Due to interactions between their gene products at the cellular or biochemical level
