Lecture 6 Flashcards
What are Alleles?
Different forms of a gene that exist at a locus
What is a Wild type allele?
The most commonly found allele in a population
What are the characteristics of a Variant of Mutant allele?
Different from wild type, may or may not adversely affect gene product, may or may not result in a detectable phenotype
What does Homozygous refer to?
Identical alleles are present on both homologous chromosomes
What is Heterozygous?
One alleles is wild type and the other is not
What is an Allelic series or Multiple Alleles?
The know mutant genes for a given gene plus its wild type allele
What are Homozygotes?
A cell or organism with identical genes of interest
What are Heterozygotes?
A cell or organism with one wild type copy and one mutant allele
What is is called when there is 2 mutant alleles that are different from each other?
Heteroallelic
Transheterozygous
Compund heterozygotes
What is Hemizygous?
A situation where a cell/organism has only one copy of a gene/locus/chromosomal region
What does Polygenic mean?
Involving multiple genes
What is does monogenic mean?
Traits controlled by one gene
What is Haplosufficiency?
One functional copy is sufficient for a wild phenotype
What is Haploinsufficiency?
When one functional copy is not sufficient for a wild type phenotype
What is codominance?
When two alleles in a diploid cell or organism show phenotypic effects
What is Hemoglobin A?
A tetramer
What is the difference between HbS and HbA?
There is a point mutation that encodes valine instead of a Glutamic acid at position 6 of the beta chain
What does having one copy of HbS do?
Provides some protection against malaria so there is a heterozygous advantage
What is complete dominance usually the result of?
Haplosufficiency
What are the 3 main mechanisms that allow mutant alleles to be dominant?
Haploinsufficiency
Dominant negative effect
Gain of function effect
What is the Dominant negative effect?
When the gene product from the mutant allele interferes with the gene product from the wild type, blocking the wild type function
What is the Gain of function effect?
The mutant allele acquires a new property not present in a the wild type allele and this new property causes a phenotype
What does an A morph refers to?
The complete loss of function of a gene
What causes an A morph?
Any mutation that abrogates the function of a gene
What are examples of class A morphs?
- A missense point mutation that abolishes all functions of the protein
- A nonsense point mutation yielding a truncated non-functional protein
- Complete deletion of an entire gene
What occurs in a Hypomorph?
The allele is still partially functional, but not at the level of the wild type gene
What is an example of a cause of a Hypomorph?
Mutation in a regulatory element may cause reduced expression of a gene or a point mutation may reduce the activity of the gene product
What are Porphyrias?
A group of diseases affecting heme production
What happens if you have no heme?
It is lethal
Why are patients who have Porphyria sensitive to light?
Because they accumulate high amounts of heme precursors that are cytotoxic
What can help Porphyria?
The injection of heme or glucose
What occurs in a Hypermorph?
A gene is active at a level higher than the wildtype gene
What is an example of a Hypermorph?
A mutation in a regulatory element may increase the expression of the gene resulting in more protein. Alternatively a mutation in the coding region may cause the protein to be hyperactive, while protein levels are comparable to the wild type
What is different about Hypermorphs?
The gene product did not gain a new property there is simply more of the normal gene product, or normal levels of the gene product with higher activity
What occurs in a Neomorph?
The allele is active but has acquired a function that the wild type gene does not have
What occurs in an Antimorph?
The allele is not only active but can override the function of the wild type allele in a heterozygous setting
What do complementation test identify?
Mutation in different genes
What are Mutations that Complement?
They are mutations that are mutant in different gene loci and are called non-allelic mutation
What are Mutations that Fail to Complement?
Mutations that are mutant in the same gene and are called allelic mutation
How are genetic mutations created?
Feed the male organism a chemical mutation
What is the most common mutagen?
Ethylmethane sulfonate to create G to A and T to C transitions
How does EMS work?
It removes the ability for a base pair to make a certain hydrogen bond which causes it to make a base pair with a different nitrogenous base
What does EMS cause?
A point mutation
What do Genetic Screen do?
Mutagenize animals to isolate new mutants
What occurs if m1 and m2 are mutations of the same gene?
Then they would not posses a wild type copy of the gene and be m1/m2 so they fail to complement each other
What occurs if m1 and m2 are mutations of different genes?
Then they would each possess a wild type copy of the gene and be m1/+;m2/+ so they complement each other
