Chapter 7 - Gene Interactions Flashcards
What is a sex influenced gene? What is an example of this?
A sex influenced gene is a gene whose expression is affected by the sex hormones.
An example is horns in sheep, where the same gene will result in different looking horns in females and males.
What is incomplete dominance?
The combination of two alleles that creates a new phenotype.
Example: red and white flowers breeding to make pink flowers.
What is codominance?
When two alleles are both expressed simultaneously.
Example: roan coat colour in horses, which is a mix of chestnut and grey hairs.
What is hierarchical domiance?
When there are multiple alleles, and their dominance is hierarchical. An example is with coat color in rabbits. Agouti is dominant to chincilla which is dominant to himalayan which is dominant to albino.
What happens when a mother is incompatible with her child during pregnancy?
As during pregnancy the child’s red blood cells enter the mother’s circulation, the blood types need to be compatible. They are incompatible when the mother is Rhessus - and the child is Rhesus +. This is not so much an issue during the first pregnancy, but for the second pregnancy, the mother’s body has developped antibodies to discar the child’s Rhesus + blood cells, causing the death of the foetus.
What is epistasis? Give an example.
Epistasis is when we start looking at dihybrid crosses, as it is when two genes interact with each other to form a particular phenotype.
An example is with coat color in dogs, where one gene determines the color and another determines the presence or absence of the pigment. Both genes affect the coat color in the dogs.
Other examples are with combs in chickens, or color in raven (corn). This also occurs in eye color.
How does epistasis work in eye color?
Eye color is determined by two genes, the HERC2 and the EYECL1, on chromosomes 15 and 19 respectively.
Chromosome HERC2: B = brown, b = blue.
Chromosome EYECL1: G = green, b = blue.
All of the combinnations of these genes creates a spectrum of possible eye colors. (This is because there are in fact 19 genes affecting eye color)
What happens when three or more genes interact?
You start to see a range of phenotypes.
What are polygenic (quantitative) traits?
Polygenic traits are when many genes interact with each other and also with the environment for one trait.
Examples include height, IQ, milk production in cattle, wool production in sheep.
Another example is with skin color in humans.
What is an example of environment interaction with genes?
In siamese cats, the color of the fur is influenced by temperature. Above 33 degrees C, the pigment is inactive, making the color of the fur white. Below 33 degrees, the pigment is active, making the color of the fur black.
What is pleiotropy?
When a single gene has more than one effect.
An example is porphyria, which can cause psychotic episodes, sensitivity to light, anaemia, and pain and seizures.
How does blood type work? What type of gene interaction is responsible for types of blood?
The AB blood type is an example of codominance, where both alleles manifest their phenotypes.
The i allele is recessive to both the IA and the IB alleles.
For rhesus factor, + is simply dominant to -.
