Lecture 24 Flashcards
How can we determine the odds of a genotype occuring using probability?
Using the chance of a parent supplying a particular allele (either 0.5, 1 or 0 based on whether homozygous (0 or 1) or heterozygous (0.5)) we can determine the probability of offspring having a specific genotype by multiplying the probabilities together, note that we must include all methods of achieving a genotype for this to work e.g If two parents are Aa the offspring could get A from the mum or the dad and a seperate probability pathway would have to be followed for each.
What are lethal alleles? What phenotypic ratio does this lead to?
Alleles which when two copies of it are received results in death. Leads to a 2:1 phenotypic ratio instead of the typical 3:1.
What is a polymorphic gene, what do they help favour?
A single gene which is controlled by many alleles. They help favour diversity.
What is incomplete dominance? What are the offspring ratios for the F1 and F2 generations of two homozygous individuals with different incomplete dominance alleles?
When two alleles mix to form an intermediate. The phenotypic ratio for F1 will be all an intermediate, the F1 will be 1:2:1 with the 1s being the grandparental types and the 2 being the intermediate.
What is co dominance? What is a notable example within humans
Co dominance is when both phenotypes co exist side by side within the organism without mixing, a notable example is the ABO blood system in humans.
What is epistasis?
Epistasis refers to when one gene affects the actions of another, typically because they are both found in the same biochemical pathway. If we take a gene B and it codes for brown colouring but will not be able to colour if gene A is not present then we say that gene B is under the epistatic control of A (Because A will be first in the biochemical pathway.
What are polygenic traits?
A phenotype controlled by many genes which have an additive effect, the characters appear continuous or quantitative. The addition of these genes is known as an additive effect.
How does environment affect phenotype? What does it do to the differences between phenotypes?
The environment supplies nutrients as well as factors such as disease, these can cause changes to phenotype (e.g nutrients mean more ability to grow tall). This environmental factor will smooth out the differences between the phenotypes.
What is pleiotropy? Give an example
Pleiotropy refers to when one gene has many symptoms, e.g the sickle cell gene causes breakdown of red blood cells, clumping of cells and clogging of small blood vessels and accumulation of sickled cells in the spleen.
What does continuous traits mean? What about discrete traits?
A continuous trait is one which can have an essentially infinite number of values (e.g skin colour) while a discrete trait is one which only has a small number of different values e.g hanging or non hanging ear lobe.
What is polymorphism?
Polymorphism refers to a non discrete trait, e.g being male or being female.
