chapter 5 Flashcards
(46 cards)
What determines the color of pepper?
The interaction of several genes
This illustrates the complexity of gene interactions in determining phenotypic traits.
What is gene discovery?
Studying a set of mutants for a trait that exhibits single-gene inheritance can identify genes involved in the trait’s development.
What are the key questions regarding gene interactions?
- How do the alleles for a gene interact?
- What are multigene pathways?
- How do separate genes interact in these pathways?
- What is the genetic test for gene interaction?
What is an allelic series?
A collection of genetic mutations for a particular gene.
Define complete dominance.
A condition where homozygous dominant (A/A) cannot be distinguished from heterozygotes (A/a).
What is an example of complete dominance?
PKU disease, where one good allele is haplosufficient.
What does haplosufficient mean?
One good allele is sufficient for normal function.
What is an example of a mutation that is recessive?
Achondroplasia, where a single wild type FGFR3 allele is haploinsufficient.
Define null allele.
An allele that produces a non-functional protein.
What is the dominant negative effect?
A situation where one bad allele interferes with the activity of the other wild type allele.
What is incomplete dominance?
A condition where an intermediate phenotype is observed in the heterozygote.
Provide an example of incomplete dominance.
Flower petal phenotype in four-o’clocks, resulting in pink flowers (c+/c).
Define codominance.
A condition where the heterozygote expresses both allele phenotypes.
What determines human ABO blood groups?
Three alleles for the same gene: I^A, I^B, and i.
What are recessive lethal alleles?
Alleles that cause an organism to die prematurely.
What is a pleiotropic gene?
A gene that contributes to several traits of an organism.
What is the one-gene-one-enzyme hypothesis?
A hypothesis proposed by Beadle and Tatum stating that each gene encodes a single enzyme.
What is the purpose of a complementation test?
To determine whether mutations are in separate genes.
What does it mean if two mutations complement each other?
The mutations are in different genes.
What is gene interaction?
When the phenotype of a double mutant is different from the sum of the two individual phenotypes.
What is epistasis?
Gene interaction where the double mutant has the same phenotype as one of the single mutants.
What phenotypic ratio suggests no gene interaction?
9:3:3:1 ratio.
What does a 9:7 phenotypic ratio indicate?
The double mutant has the same phenotype as the two single mutants, suggesting they control different steps in the same pathway.
What is a heterokaryon?
A fungal cell with two or more genetically different nuclei sharing the same cytoplasm.