Extensions On Mendelian Genetics Flashcards
Gene interaction
A phenotype is affected by more than one set of genes.
What is a common characteristic of wild-type alleles?
They are dominant.
What is the source of alleles?
Mutation.
New phenotypes results from what?
A change in functional activity of cellular product specified by that gene.
Loss-of-function mutation
A mutation that causes the wild-type to lose its function.
Null allele
The mutated allele where the loss is complete. It is nonfunctional.
Gain-of-function mutation. Most often result in what?
Mutations that enhance the function of the wild-type. Often result in dominant alleles.
Neutral mutation
A mutation that results in no phenotypic change. Only evident in DNA sequence.
What are often influenced by more than one gene and mutations in those genes?
Phenotypic traits leading to an end product.
How is wild-type indicated in genotype?
Superscript +.
What does / mean in genotype?
Allele designations represent same locus on homologous chromosomes.
Format of genotype with recessive mutant allele?
Small letter with no superscript. Wild-type contains superscript and is dominant.
Format of genotype with dominant mutant allele?
Capital letter with no superscript. Wild-type contains superscript and is recessive.
Format of genotype where no dominance exists between alleles?
Capital letters with superscripts to indicate alternative alleles.
Incomplete dominance. Also called what?
It is when no allele is dominant in a gene. It is also called partial dominance. An intermediate phenotype is generated.
Threshold effect
Normal phenotype expression occurs when a minimal level of gene product is attained.
Codominance
Both alleles in a heterozygote is expressed.
Codominance
Both alleles in a heterozygote is expressed.
Codominant inheritance is characterized by what?
The expression of gene products of both alleles.
What is needed to study codominant inheritance?
Both products must be phenotypically detectable.
Multiple alleles
Three or more alleles for same gene are present in population.
How must multiple alleles be studied?
In populations.
H substance
Compound on blood cell to which two terminal sugars are added.
Bombay phenotype
H substance is not completely synthesized. AB antigens are meaningless, automatically O blood type.
Recessive lethal allele
Allele that, when homozygous, is lethal. Prohibits a gene product that is necessary for survival.
Behavior of recessive lethal allele when heterozygous?
Acts as recessive allele, but is dominant towards phenotype. It creates a mutant phenotype.
Dominant lethal allele
Presence of one allele causes the death of an individual.
Why are dominant lethal alleles rare?
Individuals often die before they can reproduce.
Genetic linkage
Tendency that DNA sequences that are close on chromosome are inherited together during meiosis.
Method used when doing a dihybrid cross with different modes of inheritance?
Forked-line method.
Epigenesis
Each step of development increases complexity of organ or feature of interest. It is influenced by many genes.
Why are phenotypes often affected by more than one gene?
Each step of development is governed by a different gene, making the end product very complex.
Heterogenous trait
Many genes are responsible for forming a common mutant phenotype.
Epistasis
The expression of one gene masks or modifies the effect of a second gene.
Locus is epistatic to another
The alleles at the locus masks or modifies the effect of the alleles at another locus.
Locus is hypostatic to another
The effect of the alleles at the locus are masked or modified by the alleles at another locus.
Assumptions and conventions about dihybrid crosses?
- discontinuous variation
- genes
- dash
- P1 and F1
- F2
- Distinct phenotypic classes are produced
- The genes in each cross are on different chromosomes and therefore assort independently.
- A dash is used to indicate that a dominant allele is present and is expressed regardless of homozygosity and heterozygosity. Either allele may be present, no effect on phenotype.
- P1 crosses are between homozygous individuals. F1 is therefore only heterozygous.
- F2 is main focus of analysis.
Recessive epistasis
A recessive allele at a genetic locus masks or modifies the effect of alleles at another locus.
Dominant epistasis
A dominant allele at a genetic locus masks or modifies the effect of alleles at another locus.
Complementary gene interaction
Two dominant alleles “interact” to give a new phenotype.
Novel phenotype
A new phenotype that arises due to gene interaction.
“Are two mutations that yield similar phenotypes present in the same gene or in two different genes?” - What is used to answer this question?
Complementation analysis
Complementation group
All mutations determined to be present in a single gene.
Pleiotropy
A single gene has multiple phenotypic effects.
Penetrance of mutation
Percentage of individuals that show some degree of expression for the mutant genotype.
Expressivity
Range of expression of mutant genotype. “Intensity”
Genetic background
Genotype of all other related genes that may interact with gene of interest.
Position effect
Physical location of a gene in relation to other genetic material may influence its expression.
Translocation or inversion effect
Region of chromosome is relocated or rearranged.
Heterochromatin
Areas of chromosome that are condensed and genetically inactive.
How does temperature affect phenotype?
Temperature influences chemical activity and can therefore influence the gene product.
Temperature-sensitive mutations
Mutations whose expression is affected by temperature.
Conditional mutations
Phenotypic expression is determined by environmental factors.
Nutritional mutations
Mutations that prevent synthesis of nutrient molecules.
Auxotroph
A microorganism with a nutritional mutation.
Genetic anticipation
Type of genetic inheritance where the mutation severity increases over time and with generations.
What factors can modify a phenotype?
- Genotype
- Genetic background
- Temperature
- Nutrition
