1. Describe the genotypes given.

a. DD homozygous dominant
b. Dd heterozygous
c. Dd homozygous recessive
d. SS homozygous dominant
e. Yy heterozygous
f. WW homozygous dominant

2. In humans, brown eye color (B), is dominant over blue eye color (b). What are the
phenotypes of the following genotypes? In other words, what color eyes will they have?
a. BB
b. bb
c. Bb

3. Heterozyous, smooth pea pod, plant is crossed with a wrinkled pea pod plant. There are
two alleles for pea pod, smooth and wrinkled. Predict the offspring from this cross.

What is the phenotype of the parents?

What is the genotype of the parents?
Write down possible gametes

Do the Punnett square for the resultant offspring

What is the predicted genotypic ration for the offspring?
What is the predicted phenotypic ration for the offspring?
If this cross produced 50 seeds, how many would you predict to have a wrinkled pod?

4. In humans, achondroplasia “dwarfism” (D) is dominant over normal (d). A homozygous

dominant (DD) person dies before the age of one. A heterozygous (Dd) person is
dwarfed. A homozygous recessive individual is normal. A heterozygous dwarf man
marries a dwarf heterozygous woman

Do the Punnette square

Parent phenotype:
Parent genotypes:
Possible gametes:

What is the probability of having a normal child?

What is the probability that the next child will be normal?
What is the probability of having a child that is a dwarf?
What is the probability of having a child that dies at one from this disorder?
5. Pattern
a. When both parents are heterozygous, the phenotypic ratio always comes out
3:1. If one parent is homozygous recessive and the other is heterozygous, the
phenotypic ratio always comes out 1:1. Keeping this in mind see if you can solve
the next two problems.

In pea plants, yellow seeds (Y) are dominant and green seeds (y) are recessive. A pea
plant with yellow seeds is crossed with a pea plant with green seeds. The resulting
offspring have about equal number of yellow and green seeded plants. What are the
genotypics of the parents?

In another cross, a yellow seeded plant was crossed with another yellow seeded plant
and it produced offspring of which about 25% were green seeded plants. What are the
genotypes of both parents?

6. When an organism has the dominant phenotype, then its genotype cann be either
heterozygous or homozygous dominant. In order to find out we must do a test cross
using a homozygous, recessive organism.

In Dalmatian dogs, the gene for black spots is dominant to the gene for liver colored
spots. If a breeder has a black spotted dog, how can she find out whether it’s
homozygous (BB) or heterozygous (Bb) spotted dog? B = black spots, b = liver spots

If the breeder finds a black spotted dog, whose ancestry is not known, she cannot tell by
looking at the dog if it’s BB or Bb. She should find a liver spotted dog, whose genotype
must be bb and mate it with the black spotted dog in question.
7. You found a wild, black mouse. You have 24 offspring, 23 with black fur and 1 with white
fur. What was the genotype of the mouse?

If you only had 3 black offspring, can you tell what the genotype was of the suspect
mouse? Why or why not?

8. A female guinea pig is heterozygous for both fur color and coat texture ix crossed with a
male that has light fur color and is heterozygous for coat texture. What possible
offspring can they produce? Dark fur color is dominant (D) and lightfur (d) is recessive.
Rough coat texture R is dominant while smooth r is recessive.
Step 1: The guinea pig that’s heterozygous for both color and texture this means it has
one allele for each trait. Therefore its genotype would be DdRr. The other guinea pig has
light fur, since that’s a recessive trait the getotype for that mmust be dd. It’s also
heterozygous for fur texture which means a genotype of Rr. All together its overall
genotype must be ddRr.
Step 2 and 3: The Punnett square will be larger now because there are more possible
sperm and egg combinations. During the formation of sperm a D could go with a R
producing a sperm DR or a D could go with a r forming a sperm with Dr.

Light fur: d
Dark fur: D
Rough coat: R
Smooth coat: r

Female genotype: DdRr

Gametes: DR Dr dR dr
Male genotype: ddRr
Gametes: dR dr dR dr
 Step 4: what’s the genotypic ratio:

Step 5: only 4 different phenotypes because the 4 DdRr and the 2 DdRR will have dark
fur with rough coat, and the 4 with ddRr and the 2 ddRR will have light fur with rough
oat, while the 2 Ddrr will have dark fur with smooth coat and the 2 ddrr will have light
fur with smooth coat.
What’s the phenotypic ratio:

9. In humans there is a disease called Phenylketonuria which is caused by a recessive

allele. People with this allele have a defective enzyme and cannot break down the
amino acid phenylalanine. This disease can result in mental retardation or death. Let “E”
represent the normal enzyme. Also in humans in a condition called galactose intolerance
or galactosemia, which is also caused by a recessive allele. Let “G” represent the normal
allele for galactose digestion. In both disease, normal dominates over recessive. If two
adults were heterozygous for both traits (EeGg), what are the chances of having a child
that is completely normal? Has just PKU? Has just galactosemmina? Has both diseases?
10. In humans, straight hair ss and curly hair cc are codominant traits, that result in hybrids
who have wavy hair sc. Cross a curly hair female with a wavy haired male
a. Punnett square

b. Chances of having a curly haired child?

11. Some traits are coded for more than two alleles. One of them is blood type in humans.
The alleles A and B are codominant to each other and the O allele is recessive to both A
and B alleles. So a person with the genotype AA or AO will have A type of blood.

The proper way to write blood type is IAA, IBB, IAB, ii (recessive O)
a. Genotypes for blood type B?
b. For O?
c. For AB?

12. You’re blood type O and you marry someone with AB.
a. Punnett Square

b. Possible offsprings

13. In humans sex is determined by the twenty third pair of chrommosomes knowsn as “sex
chromosomes”. If you have two x-shaped (XX) chromosomes you are destined to be a
female. If you have an x and a Y-shaped (XY) chromosomes you are destined to be a
male. Since they carry diff information, any genes found on the X chromosomes are
referred to as sex-linked genes. Therefore, women will have two alleles for these genes
because they have two (XX) chrommmosommes. On the other hand, men have only one
allele for each of these genes because they have only one X chromosome (XY).
 a. In fruit flies, the gene for eye color is carried on the X chromosome. The allele for
red eyes is dominant over the allele for white eyes. If a white-eyed female fruit
fly is mated with a red-eyed male, predict the possible offspring.
b. Since the female has white eyes, she must be X’X’. the male is red-eyeed and
because he has only one X chromosome, he has only one allele for eye color. His
eyes are red so he must be RY. It means he only has one allele for eye color, so
he must be XRY. Since the allele R is present on the X chromosome only, and
there is no othere allele for eye color because the male chromosome is a Y
chromosome.
c. Punette square

d. Genotypic ratio:

14. Can a color blind female have a son that has normal vision? Color blindness is caused by
a sex-linked recessive allele. N = normal vision and n = color blind