Pleiotropy genes: genes that control multiple, seemingly unrelated features.
An example would be the Marfan Syndrome (unusual height, thin phalanges, dislocation of the lens in eyes, aortic diseases, etc.)
These traits all seem very unrelated but can be traced back to the mutation of a single gene.
Lethalallele: an allele that can have a life-threatening effect on the organism.
A example would be the yellow mouse. The yellow allele is a mutation that turns the mice's coats yellow. The yellow trait is dominant to the agouti allele. When a Punnett Square is drawn for the mice, it only produces a 2:1 ratio because homozygosity for the yellow trait is lethal.
Recessive lethal: when the recessive allele causes death or severe disease if inherited from both parents
Dominant lethal: when the dominant allele causes death or severe disease if inherited from one parent
