Transcript Polygenic Traits

Polygenic Traits
Definition
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.
Examples of Polygenic Traits
Pepper Color
Gene 1: R=red
r=yellow
Gene 2: Y=absence of chlorophyll (no green)
y=presence of chlorophyll (green)
Pepper Color
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)
Pepper Color
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
Chicken Comb Example:
4 different phenotypes result:
Rose Combs (R-pp)
Walnut Combs (R-P-)
Pea Combs (rrP-)
Single Combs (rrpp)
Try these questions:
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!
Polygenics Problem
 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!)
Let’s Review:
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.