Module 6
1. Module 6
1.39. Page 4
Module 6—Mendelian Genetics: The Transmission of Traits to the Next Generation
Lesson Summary
During this lesson you were to examine the following focusing question:
- How might multiple genes combine to form a single trait?
Multiple genes can contribute to the expression of only one trait. Two genes may combine to form a new phenotype that neither can produce on their own. One gene may also affect or control the expression of another gene by regulating a factor that is required by the other gene, such as pigment for hair cells. Many continuous phenotypes, such as corn length or bean mass, can be explained by each dominant allele of a gene collection being a greater contributor to the total. In each of these examples, more than one gene is combining to give rise to a single trait that can be observed.
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
continuous traits: traits that have a range of phenotypes, such as human height or eye colour with its many shades; is due to the polygenic effect of many genes together
epistasis: a type of polygenic inheritance where two genes collectively determine a phenotype of a trait (e.g., the B gene codes for type of colour (B = black, b = brown) and the C gene determines whether colour occurs at all (C = colour, c = no colour); three phenotypes result—white, brown, and black)
pleiotropy: the reverse of polygenic inheritance; where one gene affects the phenotypes for several traits (e.g., the PKU gene affects mental retardation, skin colour, hair colour, and other traits)
polygenic inheritance: where more than one gene (often several) are involved in determining the phenotype for one characteristic (e.g., eye colour is actually the result of multiple genes that collectively contribute to the final eye colour)