 Some traits are determined by the combined effect of two or more pairs of alleles. These traits are called polygenic traits.
 Each pair of alleles adds something to the resulting phenotype.
 Other names for polygenic traits are multifactorial traits, or quantitative traits.

Polygenic traits are continuous
 Because so many alleles contribute to the final phenotype, a variety of phenotypes can occur!
 For example, height is a polygenic trait.

Polygenic Traits are Continuos
 When dealing with polygenic traits that are only controlled by two pairs of alleles, we can complete Punnett squares to determine the genotypes and phenotypes of the F1 generation.

 Pepper Color
Gene 1: R=red r=yellow
Gene 2: Y=absence of chlorophyll (no green) y=presence of chlorophyll (green)

 Possible genotypes:
 R-/Y- : red (red/no chlorophyll)
 R-/yy : brown/orange (red/chlorophyll)
 rr/Y- : yellow (yellow/no chlorophyll)
 rr/yy : green (yellow/chlorophyll)

 Try crossing a brown pepper (RRyy) with a yellow pepper (rrYY).
 Which trait will your offspring (F1 generation) produce?
 What traits are produced when you cross two of the peppers found in the F1 generation?

More Polygenic Traits
 Chicken Combs:
 There are 4 different comb shapes that can appear in a chicken.
 Comb shape is controlled by two genes found on two different pairs of chromosomes.
 Gene 1: R
 Gene 2: P

 4 different phenotypes result:
 Rose Combs (R-pp)
 Walnut Combs (R-P-)
 Pea Combs (rrP-)
 Single Combs (rrpp)

 Indicate the phenotypes of the parents and give the genotypic and phenotypic ratios of their offspring for the following crosses: (Refer to your phenotype chart for chickens)
 rrPP x RRpp
 RrPp x RrPp

Another example of a polygenic trait:
 Hair Color
 Hair color is controlled by alleles on chromosomes 3, 6, 10, and 18.
 The more dominant alleles that appear in the genotype, the darker the hair!

 The height of plants is controlled by 4 pairs of alleles. Alleles A, B, and C contribute 3 cm to the plant's height. Alleles that are recessive do not contribute to the height. Gene L is always found in a homozygous dominant condition and always contributes 40 cm to the height.
 a) What would be the height of a plant with the genotype
AABBCCLL?
 b) What would be the height of a plant with a genotype aabbccLL?
 c) What would be the height of the offspring produced from a cross between the plants in a) and b)?
 d) What would be the heights of the offspring produced from a cross between AaBbCcLL and AaBbCcLL? (now there is a challenge!)

 Sex linked traits
 - X linked recessive
 - X linked dominant
 - y linked
 Sex influenced traits
 Polygenics
 Epistasis
 Pick up a piece of flip chart paper and a marker for your table. Summarize the new genetics topics.