Polygenic Traits Polygenic traits are continuous z Because

Polygenic Traits

Polygenic traits are continuous z. Because so many alleles contribute to the final phenotype, a variety of phenotypes can occur! z. For example, height is a polygenic trait. If you look around, you will notice there are not two set heights, but rather a continuum of height among your classmates.

Polygenic Traits are Continuos z. However, when dealing with polygenic traits that are only controlled by two or three pairs of alleles, we can complete Punnett squares to determine the genotypes and phenotypes of the F 1 generation.

Examples of Polygenic Traits z. Pepper Color Gene 1: R=red r=yellow Gene 2: Y=absence of chlorophyll (no green) y=presence of chlorophyll (green)

Pepper Color z. Possible genotypes: z. R-/Y- : red (red/no chlorophyll) z. R-/yy : brown/orange (red/chlorophyll) zrr/Y- : yellow (yellow/no chlorophyll) zrr/yy : green (yellow/chlorophyll)

Pepper Color z. Try crossing a brown pepper (RRyy) with a yellow pepper (rr. YY). z. Which trait will your offspring (F 1 generation) produce? z. What traits are produced when you cross two of the peppers found in the F 1 generation?

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

Chicken Comb Example: z 4 different phenotypes result: z. Rose Combs (R-pp) z. Walnut Combs (R-P-) z. Pea Combs (rr. P-) z. Single Combs (rrpp)

Try these questions: z 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) z rr. PP x RRpp z Rr. Pp x Rr. Pp

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

Polygenics Problem z 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. z a) What would be the height of a plant with the genotype AABBCCLL? z b) What would be the height of a plant with a genotype aabbcc. LL? z c) What would be the height of the offspring produced from a cross between the plants in a) and b)? z d) What would be the heights of the offspring produced from a cross between Aa. Bb. Cc. LL and Aa. Bb. Cc. LL? (now there is a challenge!)

Let’s Review: z Sex linked traits z - X linked recessive z - X linked dominant z - y linked z Sex influenced traits z Polygenics z Pick up a piece of flip chart paper and a marker for your table. Summarize the new genetics topics.

Next Topic…. z. Epistasis