Genetic Crosses
Define Monohybrid Cross:
Using the pea plant traits, draw 4 Punnett squares and show the
crosses for…
1.
Two homozygous dominants for flower color. Purple
dominant
2. 1 heterozygote for pod color with a homozygous recessive for
pod color. Green dominant
3. 1 homozygous dominant for pea color with a homozygous
recessive for pea color. Yellow dominant
4. 1 heterozygote with 1 heterozygote for flower color.
Write the genotypic & phenotypic ratios (GR & PR) & percentages
(G% & P%) for each.
P
P
GR
1PP:0
P
PP
PP
PR
1purp:0
P
PP
PP
G%
100%PP
P%
100%purple
G
g
GR
1Gg:1gg
g
Gg
gg
PR
1green:1yellow
g
Gg
gg
G%
50%Gg:50%gg
P%
50%green:50%yellow
Y
Y
GR
1Yy:0
y
Yy
Yy
PR
1Yellow:0
y
Yy
Yy
G%
100%Yy
P%
100%Yellow
Genetic Crosses that Involve 2 Traits -- Biology 2A
In rabbits, grey hair is dominant to white hair.
Also in rabbits, black eyes are dominant to red eyes.
GG = gray hair
Gg = gray hair
gg = white hair
P
p
GR
1PP:2Pp:1pp
P
PP
Pp
PR
3purp:1white
p
Pp
pp
G%
25%PP:50%Pp:25%pp
P%
75%purp:25%white
BB = black eyes
Bb = black eyes
bb = red eyes
1. What are the phenotypes (descriptions) of rabbits that have the following genotypes:
Ggbb ____Gray/red _____
ggbb _____white/red____
ggBB ____white/black_____
GgBb ____gray/black____
2. A male rabbit with the genotype GGbb is crossed with a female rabbit with the genotype ggBb The square is set up below.
Fill it out and determine the phenotypes and proportions in the offspring.
How many out of 16 have grey fur and black eyes? __8___
GgBb
How many out of 16 have grey fur and red eyes? ___8___
GgBb
Ggbb
Ggbb
How many out of 16 have white fur and black eyes? ___0___
How many out of 16 have white fur and red eyes? ___0____
3. A male rabbit with the genotype GgBb . Determine the gametes produced by this rabbit (the sperm would have these
combinations of alleles) Hint there are 4 combinations.
GB, gB, Gb, gb
4. A female rabbit has the genotype ggBb. Determine the gamets (eggs) produced by this rabbit.
gB, gb
5. Use the gametes from #3 and #5 to set up the Punnet square below. Put the male's gametes on the top and the female's
gametes down the side. Then fill out the square and determine what kind of offspring would be produced from this cross and
in what proportion (percentages would be fine).
GB
gB
Gb
gb
GF/BE: 6/16 = 37.5%
WF/BE: 6/16 = 37.5%
gB
GgBB
ggBB
GgBb
ggBb
BF/RE: 2/16 = 12.5%
gB
GgBB
ggBB
GgBb
ggBb
WF/RE: 2/16 = 12.5%
gb
GgBb
ggBb
Ggbb
ggbb
gb
GgBb
6. An aquatic arthropod called a Cyclops has antennae that are either smooth
or barbed. The allele for barbs is dominant. In the same organism, resistance
to pesticides is a recessive trait. Make a "key" to show all the possible
genotypes (and phenotypes) of this organism. Use the rabbit key to help you if
you're lost.
ggBb
Ggbb
Barbed = B
Smooth = b
BB = Barbed
Bb = Barbed
bb = Smooth
ggbb
Sensitive = S
Resistant = s
SS = Sensitive
Ss = Sensitive
ss = Resistant
7. A Cyclops that is resistant to pesticides and has smooth antennae is crossed with one that is heterozygous for both traits.
Show the genotypes of the parents.
___bbss___ x ___BbSs___
8. Set up a punnet square for the cross.
bs
bs
bs
bs
BS
BbSs
BbSs
BbSs
BbSs
Bs
Bbss
Bbss
Bbss
Bbss
bS
bbSs
bbSs
bbSs
bbSs
bs
bbss
bbss
bbss
bbss
9. What are the phenotypic ratios of the offspring?
¼ = Barbed – Sensitive ¼ = barbed – resistant ¼ = smooth – sensitive ¼ = smooth – resistant
10. Albino is dominant to normal skin color. Bald is dominant to hairy. Coned headed is dominant to round headed. Perform a
trihybrid cross for a male that is (He) albino that is hairy and has a (He) coned head with a female that is (He) albino, is pure
bred hairy, and has a round head.
AabbCc x Aabbcc
Male gametes: AbC Abc AbC Abc abC abc abC abc
Female gametes: Abc Abc Abc Abc abc abc abc abc
AbC
AbC
Abc
Abc
abC
abC
abc
abc
Abc
AAbbCc
AAbbCc
AAbbcc
AAbbcc
AabbCc
AabCbc
Aabbcc
Aabbcc
Abc
AAbbCc
AAbbCc
AAbbcc
AAbbcc
AabbCc
AabbCc
Aabbcc
Aabbcc
Abc
AAbbCc
AAbbCc
AAbbcc
AAbbcc
AabbCc
AabbCc
Aabbcc
Aabbcc
Abc
AAbbCc
AAbbCc
AAbbcc
AAbbcc
AabbCc
AabbCc
Aabbcc
Aabbcc
abc
AabbCc
AabbCc
Aabbcc
Aabbcc
aabbCc
aabbCc
aabbcc
aabbcc
abc
AabbCc
AabbCc
Aabbcc
Aabbcc
aabbCc
aabbCc
aabbcc
aabbcc
abc
AabbCc
AbabCc
Aabbcc
Aabbcc
aabbCc
aabbCc
aabbcc
aabbcc
abc
AbabCc
AabbCc
Aabbcc
Aabbcc
aabbCc
aabbCc
aabbcc
aabbcc
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