Download Two trait crosses - Sonoma Valley High School

Two trait genetic crosses & pedigrees
Crossing Two Traits
Cross a
heterozygous
purple,
heterozygous
smooth corn plant
with a corn plant
that is yellow and
wrinkled.
Purple =
P
Yellow =
p
Smooth =
S
Wrinkled = s
P = PpSs x ppss
P = PpSs x ppss
ps
PS
Ps
pS
ps
x
Step #1
Determine
genotypes of
parents.
Step #2
Determine the
gametes of each
parent.
Step #3
Set up Punnett
Squares
PpSs
ps
ppss
PS
PpSs
25% Purple & Smooth
Ps
Ppss
25% Purple & Wrinkled
pS
ppSs
25% Yellow & Smooth
ps
ppss
25% Yellow & Wrinkled
What is a dihybrid cross?
P = TtAa x TtAa
tA
ta
TA
Ta
TA
TTAA
TTAa
TtAA
TtAa
Ta
TTAa
TTaa
TtAa
Ttaa
tA
TtAA
TtAa
ttAA
ttAa
ta
TtAa
Ttaa
ttAa
ttaa
Dihybrid Cross
Ratio
9/16 Tall & Axial (Dom &
Dom)
3/16 Tall & Terminal
(Dom & Rec)
3/16 Short & Axial (Rec
& Dom)
1/16 Short & Terminal
(Rec & Rec)
Pedigrees
• A pedigree is a type of family tree that
shows the sex of the individuals and
the phenotype of that individual for a
single trait
• Circles are female ,squares are male
• Filled in has the ‘affected’ phenotype,
open has the ‘unaffected’
• The trait examined can either be
dominant or recessive
• A person who has the trait but does
not express it is a “carrier”
• (heterozygous for a recessive
trait)
Using Pedigrees
• A pedigree can be used to determine the genotype of individuals in a family
• It can be used to track a, dominant, recessive , or sex-linked trait
• Pair share: is the trait dominant or receive? How do you know? If it is recessive are
there any carriers?
What does this pedigree tell us?
White board Review
1. What are the 3 steps of determining a
dihybrid cross?
2. What does “di” mean?
3. What is a pedigree?