Download Name: Review Guide Genetics Review of Monohybrid Crosses 1

Name:__________________________________
Review Guide
Genetics
Review of Monohybrid Crosses
1. The gene for freckles (F) is dominant over the gene for no freckles (f). Using this information,
show a cross between one person who is heterozygous for the trait and another who is
homozygous for the trait.
a. All possible genotypes ______________________
b. Genotypic ratio ____________________________
c. All possible phenotypes _____________________
d. Phenotypic ratio ____________________________
e. What is the probability of the two individuals having
a child with freckles? __________________________
2. Now, cross two people who are heterozygous with the alleles mentioned in question 1.
a. All possible genotypes _______________________
b. Genotypic ratio ____________________________
c. All possible phenotypes ______________________
d. Phenotypic ratio ____________________________
e. What is the probability that a child will be born with no
freckles? ___________________________________
3. Consider the following cross:
yellow pea plants x green pea plants
all yellow pea plants
most yellow pea plants and some green plants
a. Which color is recessive, green or yellow? _________
b. If the F1 generation has 4 plants, how may should be
yellow? (Give an actual number, not a percentage.)
____________________
c. If the F1 generation has 80 plants, how many should be
yellow? (Give an actual number, not a percentage.)
4. You observe, among a group of offspring, that there are 74 purple flowers and 68 white
flowers. (P = purple, p = white)
Give the phenotypic ratio of the offspring ____________________
Give the most likely parental genotypes _____________________
Give the most likely parental phenotypes ____________________
5. You observe, among a group of puppies, that there are 6 with dark coats and 2 with light coats.
(D = dark and d = light)
Give the phenotypic ratio of the offspring ____________________
Give the most likely parental genotypes _____________________
Give the most likely parental phenotypes ____________________
6. In sesame plants, the one-pod condition (P) is dominant to the three-pod condition (p), and
normal leaf (L) is dominant to the wrinkled leaf (l). The offspring produced in one cross yield
223 one-pod normal, 72 one-pod wrinkled, 76 three-pod normal, 27 three-pod wrinkled.
Give the phenotypic ratio of the offspring ____________________
Give the most likely parental genotypes _____________________
Give the most likely parental phenotypes ____________________
7. In a fictitious organism called a “tribble,” red color is dominant over white. A normal red
tribble is crossed with one that does not have the color. The offspring that result are 8 tribbles, all
of which born with red color. Use this information to provide the most probable parental
genotypes.
____________________________________
8. In dogs, spots on body (T) are dominant over no spots (t). Dark eyes (D) are dominant over
blue eyes (d). Two blue eyed dogs are crossed to produce 10 puppies with spots and 11 puppies
with no spots.
What is the most probable genotype for the
parents for eyes and spots?
____________________________________
9. Complete the following 4x4 Punnet square, showing all the possibilities of gametes that can
result from these two heterozygote parents. After you complete the square, then determine the
phenotypic ratio at the bottom. (P = purple, p = white, S = smooth, s = wrinkled)
10. In the previous problem, the gametes that resulted from the parent (PpSs) included PS, Ps,
pS, and ps. Determine the gametes that would result from each of the following genotypes for
possible parents:
a. PpGg _________________________________
b. ppGg _________________________________
c. Llbb__________________________________
d. aagg___________________________________
11. Show a cross between the following dogs, making sure to construct a Punnet square in the
space provided. (D= dark eyes, d= blue eyes; W= wire hair, w= shaggy hair)
DdWw x DDWw
a. Possible phenotypes ___________________________
b. Phenotypic ratio ______________________________
12. A man and woman are going to have children. The woman is homozygous for type A and the
man is homozygous for type B. Show a Punnett square that illustrates this cross and then answer
the following.
a. Possible genotypes ___________________________
b. Genotypic ratio ______________________________
c. Possible phenotypes __________________________
d. Phenotypic ratio ______________________________
e. Chance of having a child with O blood ____________
13. In a case in Spokane, Washington, a young woman accused a soldier of being the father of
her child. The soldier, of course, denied it. The soldier’s lawyer demanded that blood types be
taken to prove the innocence of his client. The following were obtained: Alleged father- Type O.
Mother- Type A. Child- Type AB. The court found the soldier guilty on the basis of the woman’s
remarkable memory for dates and details that apparently eliminated all other possible fathers.
a. Possible genotypes for these people
_______________________________
b. Do you agree with the court’s decision? Why or why
not?
14. Horses have different alleles for body color, but two of these alleles include the chestnut
(dark brown) allele and a diluting (pale cream) allele (often incorrectly called ‘albino’), which
display incomplete dominance. A horse heterozygote for these two alleles is a palomino. (Let C=
chestnut, P= pale) Illustrate a cross between two palominos.
a. In the space provided on the left, draw a Punnett
square to illustrate the cross.
b. Genotypic ratio __________________________
c. Phenotypic ratio _________________________
d. Probability that the offspring will be a pale
horse? _____________________________
e. Draw a Punnet square on the left to illustrate the
cross between a palomino and a chestnut horse.