Genetic cross/ Dominance Flashcards
Give the molecular explanation for incomplete dominance in snapdragon flowers?
Unlike pea plants, the coloration in snapdragons is dosage sensitive. The Rr heterozygote has half as much enzyme as an RR homozygote, so the colour is half as strong.
So therefore homozygous Red vs homozygous White= all pink.
give a basic description of codominance
sharing information between alleles.
non-interfering functions and thus both can act simultaneously.
Give a molecular explanation of codominance…
Blood group antigens are molecular “flags” that the body uses to recognise which cells are “self” and which are foreign.
The “flags” consist of chains of sugar molecules attached to the cell surface.
Basic white flag is a chain of 5 sugar molecules which is further modified by the enzyme encoded by the ABO gene.
It terms of phenotypes describe the difference between co-dominance and incomplete dominance?
In codominance the phenotype for an F1 heterozygote resembles both parents simultaneously.
However, in incomplete dominance the phenotype for the F1 heterozygote is intermediate to the homozygous parents.
When is the incomplete dominance called semi-dominant?
If the heterozygote phenotype is half way between the homozygous parent phenotypes.
Give an example of underdominance?
Hybird of horse and donkey to aim to increase offspring results in a different species called a mule, which is sterile(no offspring).
What are the foundations to underdominance and overdominance
If the hybrid offspring have lower fertility / lower vigour, this is called underdominance
If the hybrid offspring have higher fertility / greater vigour, this is called overdominance.
Show how Darwin’s finches relate to Underdominance and overdominance?
Hybrid finches with intermediate shape beak show incomplete dominance.
Hybrid finches do not durvive well and leave few offspring due to less advantage in feeding.
Called HYBRID INCOMPATIBILITY.
What is polygenic inheritance?
Phenotype is not determined by one gene but by the interaction of multiple genes.
Each allele contributes only partially to the overall phenotype.
The more genes involved, the more complex the inheritance pattern will be.
The effect of the genes may be additive or epistatic.
Define epistatic
Expression of one phenotype is affected by another phenotype
e.g albinism
Give an example of an additive effect from an allele of a gene.
Example: Skin Colour
Gene A(2 allleles) generates 0,1 or 2 units of melanin.
Gene B also generates another0, 1 or 2 units of melanin.
Gene C likewise
What are the different types of epistasis?
Dominant epistasis: the dominant effects of one gene masks the effects of another
Recessive epistasis: the recessive effects of one gene masks the phenotypic effects of another
In dominant epistasis how many copies of an allele are needed for suppression of another gene?
Single copy
In recessive epistasis how many copies of an allele are needed for suppression of another gene?
Two copies.
