Part A: Vocabulary
Match the definitions on the left with the terms on the right.
__D__ 1. genotypes made of the same alleles
A. alleles
___A_ 2. different forms of genes for a single trait
B. dominant
__B__ 3. gene that is always expressed
C. heterozygous
___E_ 4. gene that is expressed only in the homozygous state D. homozygous
__C__ 5. genotypes made of two different alleles
E. recessive
Below each of the following words are choices. Circle the choices that are examples of each of
those words.
6. Dominant allele: D e k L N n R S
7. Recessive allele: M n d F G r k P
8. Homozygous dominant: AA Gg KK mm uu Rr TT
9. Homozygous recessive: ee Ff HH Oo qq Uu ww
10. Genotypes in which dominant gene must show: AA Dd EE ff Jj RR Ss
11. Genotypes in which recessive gene must show: aa Gg Ff KK rr Oo Tt
Part B: Punnett Squares
12. Examine the following Punnett squares and circle those that are correct.
13. What do the letters on the outside of the Punnett square stand for? ____parents’ genotypes__________
14. In tomatoes, red fruit (R) is dominant over yellow fruit (r). A plant that is homozygous for
red fruit is crossed with a plant that has yellow fruit. What would be the genotypes and phenotypes of the P1 and
F1 generations?
P1
genotypes:
Phenotypes
RR
Red
rr
yellow
F1
genotypes:
Rr
Phenotypes
Red
Monohybrid Cross
15. A heterozygous, 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.
a. What is the genotype of the parents? ____Ss x ss__
b. Set up a Punnett square with possible gametes.
S
s
s
Ss
ss
s
Ss
ss
c. Fill in the Punnett square for the resultant offspring.
d. What is the predicted genotypic ratio for the offspring ?____0:2:2__________ (homo dom: heter: homo rec)
e. What is the predicted phenotypic ratio for the offspring ?____2:2______________ (dominant: recessive)
f. If this cross produced 50 seeds how many would you predict to have a wrinkled pod?
50 seeds x .5 = 25 seeds
Dihybrid Cross
16. In pea plants, the round seed allele is dominant over the wrinkled seed allele, and the yellow seed
allele is dominant over the green seed allele. The genes for seed texture and those for seed color
are on different chromosomes. A plant heterozygous for seed texture and seed color is crossed
with a plant that is wrinkled and heterozygous for seed color. *R = round, r = wrinkled, Y=
yellow, y = green
a. Construct a Punnett square for this cross.
RY
Ry
rY
ry
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
b. What is the expected phenotypic ratio for the offspring?
_____6:2:6:2_____________________________
(dominant both: dominant in first and recessive in second: recessive in first and dominant in
second: recessive in both)
Codominant
17. 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. Complete a Punnett square for this cross.
c
c
s
sc
sc
c
cc
cc
b. Probability of child having wavy hair? _____50%_____
c. Probability of child having curly hair? _____50%_____
d. Probability of child having straight hair? _____0%_____
Multiple Alleles
18. So far we have studied traits or genes that are coded for by just two alleles. Like in rabbits, there was
one allele for brown hair color and one allele for white hair. However, some traits are
coded for by more than two alleles. One of these is blood type in humans. This is a violation of
Mendel’s Principle of unit characteristics. In humans, there are four types of blood; type A, type B, type
AB, and type O. 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.
a. What possible genotypes will produce B type of blood? _________BB, BO_______________
b. What is the only genotype that will produce O type of blood? ______OO______________
c. What is the only genotype that will produce AB type of blood? ______AB_____________
19.You are blood type O and you marry a person with blood type AB.
a. Complete a Punnett square for this cross.
O
O
A
AO
AO
B
BO
BO
e. List the possible blood types (phenotypes) of your offspring. _type A or type B____
Sex – linked
20. Hemophilia is a sex-linked trait. A person with hemophilia is lacking certain proteins that are
necessary for normal blood clotting. Hemophilia is caused by a recessive allele so use “N” for
normal and “n” for hemophilia. Since hemophilia is sex-linked, remember a woman will have
two alleles (NN or Nn or nn) but a man will have only one allele (N or n). A woman who is
heterozygous (a carrier) for hemophilia marries a normal man:
a. What are the genotypes of the parents? Woman: XNXn
Man: XNY
b. Make a Punnett square for the above cross.
XN
Xn
XN
XNXN
XnXN
Y
XNY
XnY
c. What is the probability that a male offspring will have hemophilia? ____50%______
d. What is the probability of having a hemophiliac female offspring? _____0%____
21. For each term listed below, label whether they are describing mitosis, meiosis, or both.
1. Produces haploid cells
Meiosis
2. Occurs in germ cells
Meiosis
(produces sex cells)
3. Occurs in plant and animal cells
Both
4. In humans, produces cells with 23 chromosomes
Meiosis
5. Involves cellular division
Both
6. DNA is copied once
Both
7. Occurs in body (somatic) cells
Mitosis
8. Produces 4 cells
Meiosis
9. Produces cells that are identical to each other
Mitosis
10. Homologous chromosomes line up paired with
Meiosis
each other
11. Cell divides only once
Mitosis
12. Produces diploid cells
Mitosis
13. Produces 2 cells
Mitosis
14. Has 2 separate divisions
Meiosis
15. New cells are different from each other
Meiosis
16. In humans, produces cells with 46 chromosomes
Mitosis
17. Homologous chromosomes do not line up next to
Mitosis
each other