Polygenic Inheritance
10.3.1 Define polygenic inheritance
 Polygenic
inheritance refers to a single characteristic that is controlled by more
than two genes (also called multifactorial inheritance)
 Polygenic inheritance patterns normally follow a normal (bell-shaped) distribution
curve - it shows continuous variation
 By increasing the number of genes controlling a trait, the number of phenotype
combinations also increase, until the number of phenotypes to which an
individual can be assigned are no longer discrete, but continuous
10.3.2 Explain that polygenic inheritance can contribute to continuous variation using
two examples, one of which must be human skin colour
Human Skin Colour
 The
colour of human skin is determined by the amount of dark pigment (melanin)
it contains
 At least four (possibly more) genes are involved in melanin production; for each
gene one allele codes for melanin production, the other does not
 The combination of melanin producing alleles determines the degree of
pigmentation, leading to continuous variation
TED Talks: Inheritance of Human Skin Colour
Grain Colour in Wheat
 Wheat
grains vary in colour from white to dark red, depending on the amount of
red pigment they contain
 Three genes control the colour and each gene has two alleles (one coding for red
pigment, the other coding for no pigment)
 The most frequent combinations have an equal number of 'pigment producing'
and 'no pigment' alleles, whereas combinations of one extreme or the other
are relatively rare
 The overal pattern of inheritance shows continuous variation
Polygenic Inheritance of Grain Wheat Colour