ANSWERS – More Review Part 1
For each of the following determine the percentage of genotypes, genotype terms, and
phenotypes.
Monohybrids
1. A homozygous white rabbit (b) is crossed with a heterozygous black rabbit (B).
b
B Bb
b bb
50% Heterozygous Black,
50% homozygous white
b
Bb
bb
2. A true breed tall plant is crossed with a short plant. Tall is dominant.
T
T
t Tt
Tt
t Tt
Tt
100% Heterozygous tall
Dihybrid
In kangaroo rats brown color is dominant (B) and white color is recessive. The ability to jump is
dominant (J), the ability to waddle is recessive. If a white, waddling kangaroo rat is mated with
a heterozygous brown, jumping mouse – what are the probabilities of the genotypes and
phenotypes of the offspring.
BJ
Bj
bJ
bj
bj
BbJj
Bbjj
bbJj
bbjj
bj
BbJj
Bbjj
bbJj
bbjj
bj
BbJj
Bbjj
bbJj
bbjj
bj
BbJj
Bbjj
bbJj
bbjj
BbJj- 25%, brown, jumping
Bbjj- 25%, brown, waddle
bbJj- 25%, white, jumping
bbjj- 25%, white, waddle
Intermediate
1. Tulips are incompletely dominant, so red (R) and yellow (Y) are both incompletely dominant
traits. If a hybrid is present, one will see orange tulips. What are the genotype and phenotype
percentages of crossing a pure red with a pure yellow tulip.
R
R
Y RY
RY
Y RY
RY
100% Heterozygous RY- 100% orange
1. The lubber grasshopper is a very large grasshopper, and is black with red and yellow
stripes. Assume that red stripes are expressed from the homozygous CR genotype,
yellow stripes from the homozygous CY genotype, and both from the heterozygous
genotype. What will be the phenotypic ratio of the F1 generation resulting from a cross
of two grasshoppers, one red & one with both red and yellow stripes?
CR
CR
R
R
C C
CR CR
CY CR CY
CR CY
50% CRCR - red strip, 50% both CR CY
CR
Multiple Alleles
1. In cattle hair color shows codominance. Red CR is dominant, and white CW is recessive. In the
heterozygous condition codominance is shown as a roan (something of a light red) coat. If two
roan cattle are crossed - what is the percent chance of each phenotype? Of each genotype?
CR
CW
CR CR CR
CR CW
W
R
W
C
C C
CW CW
25% red - CR CR 50% roan-CR CW 25% white-CW CW
2. George is blood type AB. His father was blood type O and his mother was blood type AB.
What were the genotypes of his parents and what are the possible blood types and ratios
expected for crosses involving these parental genotypes? Is George their child?
i
IA i
IB IB i
Probably not. 50% A, 50% B
Polygenic Inheritance
IA
i
IA i
IB i
1. Melanin is coded for when the gene L, M, or N is present. The more of these genes are
present, then the darker the skin the individual. The darkest skin possible would be
LLMMNN while an albino would be XXXXXX. Write the following names from darkest to
lightest skin.
______4____ LXMMXX- Baljeet
_____5____ LXMXXX- Candace
______2____ LLMXNN- Perry
_____6____ XXMXXX- Ferb
______1____ LLMMNN - Phineas
_____3____ LXMMNX- Isabella
ANSWERS Part 2 Review
Monohybrids
For each cross determine the genotype, genotype terms, phenotypes as well as percentages of
each.
1. A homozygous black rabbit is crossed with a heterozygous black rabbit. White is recessive.
B
B
B
BB
BB
b
Bb
Bb
50% Homozygous black (BB); 50% Heterozygous black
2. A hybrid tall plant is crossed with a short plant. Short is recessive.
T
t
t
Tt
tt
t
Tt
tt
50% heterozygous tall (Tt); 50% homozygous short (tt)
Dihybrids
In rattlesnakes brown diamonds is dominant (B) and gray diamonds is recessive. The ability to
sidewind is dominant (S), the ability to crawl is recessive. If a gray diamond, crawling
rattlesnake is crossed with a heterozygous brown diamond, sidewinding rattlesnake– what are
the probabilities of the genotypes and phenotypes of the offspring. bbss X BbSs
bs
bs
bs
bs
BS
BbSs
BbSs
BbSs
BbSs
Bs
Bbss
Bbss
Bbss
Bbss
bS
bbSs
bbSs
bbSs
bbSs
bs
bbss
bbss
bbss
bbss
25% BbSs – brown, sidewinding
25% Bbss – brown, crawling
25% bbSs – gray, sidewinding
25% bbss – gray, crawling
Incomplete & Codominance
1. Lilies are incompletely dominant, so white (W) and purple (P) are both incompletely
dominant traits. If a hybrid is present, one will see lilac tulips. What are the genotype and
phenotype percentages of crossing a pure white with a lilac tulip.
W
W
P PW
PW
W WW
WW
2. In unicorns, both the horn and wings are codominannt. Assume that horns are expressed
from the homozygous CH genotype, wings from the homozygous CW genotype, and both from
the heterozygous genotype. What will be the phenotypic ratio of the F1 generation resulting
from a cross of two unicorns, one with a horn & one with a horn & wings?
CH
CH
CH
CH CH
CH CH
CW
CH CW
CH CW
H
H
–
50% horns C C & 50% Horns & wings CH CW Ratio 1:1
Blood Types
Person
Father
Child
Mother #1
Mother #2
Genotype
IAi
ii
A
I IB
IAi
Blood type
A+
OABB+
1. A lawyer is collecting evidence in a maternity case to determine who the child’s father is. The
above table shows the people involved in the case as well as their genotypes & blood types.
a. Using Punnett squares, show who would most likely be the mother of the child.
Mother #2 to get the ii / O blood type.
IA
i
IA IA IA
IA i
A
i I i
ii
b. If Mother #1 and a O+ man were to have children, what are the possible blood types of their
children as well as the probabilities for each blood type?
IA
IB
i IAi
IBi
i IAi
IBi
Pedigree: Recessive Trait (Autosomal – body chromosome)
Cystic Fibrosis is a recessive trait (c) causing poor absorption due to pancreatic insufficiency and
recurrent pulmonary infection with progressive respiratory insufficiency, usually leading to death in
early adulthood.
1. Using a Punnet Square explain why none of the Generation II offspring have the disease?
All carriers
C
C
c Cc
Cc
c Cc
Cc
2. Explain what the relationship is between Generation III #2 and Generation III #3? Cousins
who got married
3. What is the Punnett square for the marriage of Generation III #2 & #3?
C
c
C CC
Cc
c Cc
cc
What is the chance of having a child with cystic fibrosis? 1 in 4
How does that percentage compare with the actual percentage of children with CF in
generation IV?
Predicted is 25% actual is 67%
Pedigree: Sex-linked Trait
Generation I
#1
#2
Generation II
Generation III
Red-green color blindness is an X-linked, recessive trait (Xb).
1. What are the probabilities for each couple (#1 & 2) in generation II to have sons with
colorblindness?
#1 Xr
Y
#2 XR
Y
R
R
r
R
r
R
r
X X X
X Y
X X X
Xr Y
Xr Xr Xr
Xr Y
Xr XR Xr
Xr Y
Sons for colorblindness- Couple #1 – 50%. Couple #2 100%
2. What are the probabilities for each couple in generation II (#1 & 2) to have daughters with
colorblindness? Daughters for colorblindness- Couple #1 – 50%. Couple #2 - 0%
3.How does the actual risk for colorblindness for couple # 1 differ from what actually
happened?
#1 has a 50% chance of colorblind offspring- 50%