Transcript 2 Advanced Geneticsx

Chapter 11
Advanced Genetics
Codominance
Multiple Allele Traits
Polygenic Inheritance
Lethal Alleles
Epistatic Alleles
Incomplete
Dominance
Traits appear to
"blend" in offspring
RR x WW
RW (pink)
Show:
Pink x Red
Pink x Pink
White x White
Figure 11.14
This illustrates
another style of
"letters" to denote
genotypes
R1 and R2
Don’t let letter
conventions throw
you off on the AP
test.
ROAN COW What happens when you cross a white and a red cow?
Roan is codominant - both alleles R and W are expressed
What happens when two Roan Cows
are Crossed?
Blood Types - Multiple Alleles
When doing blood type crosses, you will need to know whether at
type A or B person is heterozygous or homozygous. Type O's are
automatically OO and type AB is automatically AB. Crosses are
performed the same as any other.
Show Crosses:
AB x AO
AO x BO
AA x AB
Determine the genotypes of these
aliens given that the trait is controlled
by multiple alleles.
Polygenic Traits - controlled by many genes
● Each allele intensifies or diminishes the phenotype.
● Variation is continuous or quantitative (adding up) - also called
quantitative inheritance
● Seed Color in wheat - aabbcc, Aabbcc, AaBbcc, AaBbCc, AABbCc,
AABBCC (light, intermediate colors, dark)
● In humans - hair color, height, skin color
Pg 197
Polygenic Inheritance
AABBCC x aabbcc (P)
AaBbCc x AaBbCc (F1)
Seven Possible Phenotypes in the F2
Figure 11.16
Figure 11.17
Environment and Phenotype
Temperature, water, food sources can have an affect on how a gene is
expressed
Rabbits have a gene that codes for darker pigments - this
gene is more active at low temperatures. Parts of the body
that are colder will develop the darker pigmentation - ears
and feet
Figure 11.18b
SIAMESE CATS
Sex Linked Genes
Genes located on the X chromosome are
inherited with that X. When doing crosses you
must include the sex chromosomes in your
cross. Use superscript letters for the allele.
Example: In fruit flies, eye color is a sex linked
trait. Red is dominant to white.
Females
XRXR
XRXr
XrXr
Males
XR Y
Xr Y
White eyed male x red eyed female: XrY
x
Red eyed male x white eyed female: XRY
XR X R
x
Xr Xr
EPISTATIC ALLELES
In labrador retriever, coat color is determined by one gene with four
different alleles. Five different colors result from the combinations of
these alleles.
Black is dominant to
chocolate B or b
Yellow is recessive and
epistatic
(when present, it blocks the
expression of the black and
chocolate alleles)
E or e
Yellow Lab
Black Lab
Chocolate Lab
BBee
Bbee
bbee
BBEE
BbEE
BBEe
BbEe
bbEE
bbEe
1. A black lab (BBEe) x
yellow lab (bbee)
2. A chocolate lab (bbEe) x black
lab (BbEe)
3. Two black labs (BBEE x BbEe)