Genetics Practice Test
Part 1- Problems
For each of the following determine the percentage of genotypes, genotype terms, and phenotypes.
1. A homozygous white rabbit (b) is crossed with a heterozygous black rabbit (B).
2. A true breed tall plant is crossed with a short plant. Tall is dominant.
3. 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.
4. 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.
5. 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 CRgenotype, 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 yellow stripes?
6. 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?
7. 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?
8. 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. If Phineas and Isabella get married – what are the darkest and lightest genotypes possible.
LXMMXX- Baljeet / LXMXXX- CandaceLLMXNN- Perry / XXMXXX- Ferb
LLMMNN - Phineas / LXMMNX- Isabella
9. Duchenne muscular dystrophy (DMD) is an inherited disorder that involves muscle weakness, which quickly gets worse. It is a sex-linked recessive genetic disorder. Two normal, parents have three children: 2 boys and 1 girl. One boy has DMD while the other two are normal. What are the genotypes of the parents? What is the likelihood that another girl would have DMD? Another boy would have DMD? (Use D / d as the alleles)
10. A chromosome has the following genes: LMNOPQRST. Using the MNO segment demonstrate
a. Inversionb. Deletionc. Duplication
Part 2- Content
True-False
_____ 1. Offspring of the P1 generation are called F2 generation.
_____ 2. The law of segregation states that alleles separate during the formation of gametes.
_____ 3. The law of independent assortment states that alleles for different characteristics
are distributed to gametes in pairs.
_____ 4. An organism that is homozygous for flower color could have the genotype Qq.
_____ 5. Codominance occurs when both alleles for a gene are expressed in a
heterozygous offspring, such as would be seen in checkered feathers.
Multiple Choice Write the letter of the most correct answer in the blank.
_____ 6. In a monohybrid cross between a homozygous dominant parent and a homozygous
recessive parent, one would predict the offspring to be
a.) 3:4 homozygous dominant.c.) 1:4 homozygous recessive.
b.) 2:4 heterozygous.d.) all heterozygous.
_____ 7. In guinea pigs, black fur is dominant. A black guinea pig is crossed with a white
guinea pig. If the litter contains a white offspring, the genotype of the black-haired parent is probably
a.) homozygous dominant.c.) homozygous recessive.
b.) heterozygous.d.) None of the above.
_____ 8. Segregation of alleles occurs during
a.) mitosis.b.) meiosis.c.) fertilization.d.) pollination
_____ 9. If two parents with dominant phenotypes produce an offspring with a recessive
phenotype, then probably
a.) both parents are heterozygous.c.) both parents are homozygous.
b.) one parent is heterozygous.d.) one parent is homozygous.
_____10. A trait occurring in 400 offspring out of a total of 1,600 offspring has a probability
of
a.) .04.b.) .25.c.) .50.d.) .75.
_____ 11. Suppose you have found a new species of plant. Some of the plants have yellow
flowers, and some have red flowers. You cross a red-flowering plant with a yellow-
flowering plant. All of the offspring have orange flowers. Suggest a possible genotype for the offspring.
a.) RYb.) Rrc.) rrd.) YY
ANSWERS Genetics Practice Test
For each of the following determine the percentage of genotypes, genotype terms, and phenotypes.
1. A homozygous white rabbit (b) is crossed with a heterozygous black rabbit (B).
b / bB / Bb / Bb
b / bb / bb
50% Heterozygous Black,
50% homozygous white
2. A true breed tall plant is crossed with a short plant. Tall is dominant.
T / Tt / Tt / Tt
t / Tt / Tt
100% Heterozygous tall
3. 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 / bjBJ / 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
4. 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 / RY / RY / RY
Y / RY / RY
100% Heterozygous RY- 100% orange
5. 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 CRgenotype, 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 / CRCY / CR CY / CR CY
CY / CR CY / CR CY
100% CRCR - red stripe
6.. 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 / CWCR / CR CR / CR CW
CW / CR CW / CW CW
25% red - CR CR 50% roan-CR CW 25% white-CW CW
7. 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 / iIA / IA i / IA i
IB / IB i / IB i
Probably not. 50% A, 50% B
8. 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
LLMMNN (darkest) to LXMMNX (Lightest) / _____3____ LXMMNX- Isabella
9. Duchenne muscular dystrophy (DMD) is an inherited disorder that involves muscle weakness, which quickly gets worse. It is a sex-linked recessive genetic disorder. Two normal, parents have three children: 2 boys and 1 girl. One boy has DMD while the other two are normal. What are the genotypes of the parents? What is the likelihood that another girl would have DMD? Another boy would have DMD? (Use D / d as the alleles)
XD Y and XD Xd 0% for a girl, 50% for a boy
#1 / XDXD / XD XD / XD Y
Xd / XD Xd / Xd Y
10. A chromosome has the following genes: LMNOPQRST. Using the MNO segment demonstrate
a. Inversionb. Deletionc. Duplication
LONMPQRSTLPQRSTLMNOMNOPQRST
Part 2- Content
True-False
__F___ 1. Offspring of the P1 generation are called F2 generation.
___T__ 2. The law of segregation states that alleles separate during the formation of gametes.
___F__ 3. The law of independent assortment states that alleles for different characteristics
are distributed to gametes in pairs.
__F___ 4. An organism that is homozygous for flower color could have the genotype Qq.
___T__ 5. Codominance occurs when both alleles for a gene are expressed in a
heterozygous offspring, such as would be seen in checkered feathers.
Multiple Choice Write the letter of the most correct answer in the blank.
__D___ 6. In a monohybrid cross between a homozygous dominant parent and a homozygous
recessive parent, one would predict the offspring to be
a.) 3:4 homozygous dominant.c.) 1:4 homozygous recessive.
b.) 2:4 heterozygous.d.) all heterozygous.
__B___ 7. In guinea pigs, black fur is dominant. A black guinea pig is crossed with a white
guinea pig. If the litter contains a white offspring, the genotype of the black-haired parent is probably
a.) homozygous dominant.c.) homozygous recessive.
b.) heterozygous.d.) None of the above.
___B__ 8. Segregation of alleles occurs during
a.) mitosis.b.) meiosis.c.) fertilization.d.) pollination
__A___ 9. If two parents with dominant phenotypes produce an offspring with a recessive
phenotype, then probably
a.) both parents are heterozygous.c.) both parents are homozygous.
b.) one parent is heterozygous.d.) one parent is homozygous.
___B__10. A trait occurring in 400 offspring out of a total of 1,600 offspring has a probability
of
a.) .04.b.) .25.c.) .50.d.) .75.
___A__ 11. Suppose you have found a new species of plant. Some of the plants have yellow
flowers, and some have red flowers. You cross a red-flowering plant with a yellow-
flowering plant. All of the offspring have orange flowers. Suggest a possible genotype for the offspring.
a.) RYb.) Rrc.) rrd.) YY
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