monohybrid cross - only
keep track of one trait
at a time
dihybrid cross - keep
track of 2 different
traits at the same time
tall (T)
short (t)
green peas yellow peas
(y)
(Y)
green pods
(G)
yellow pods
(g)
inflated
pods (I)
constricted
pods (i)
round
peas
(R)
wrinkled
peas
(r)
terminal
flowers
(a)
axial
flowers
(A)
transparent
seed coat
( c)
colored
seed coat
(C)
black
(B)
white
(b)
long fur
(s)
short fur
(S)
Steps for doing genetic crosses
1. Write the genotypes
for each parent.
2. Write all the possible
gametes each parent can
produce.
TR Tr tR
tr
TR Tr
tR
tr
3. Place the gametes on a
Punnett's square.
4. Fill in each box with
both genotype and
phenotype.
5. Write the phenotypic
ratio.
TR Tr tR
tr
TTrr
TTRr
TtrR
Ttrr
Tr
tr
tall
round
tall
wrinkled
tTrR
tall
round
tTrr
tall
wrinkled
tall
round
ttrR
short
round
tall
wrinkled
ttrr
short
wrinkled
incomplete dominance (codominance) neither
gene completely hides
the other