Download Basic Genetics Practice Problems Key

Name ____________________________________________ Date ______________________ Per _________
Basic Genetics Practice Problems
1. Match the term with the correct definition.
A. Dominant Trait
___E___ Portion of DNA which codes for a protein, which leads to a trait.
___F___ The different forms of a gene, represented by letters.
B. Recessive Trait
C. Genotype
___A___ The trait which appears in the F1 hybrid generation.
D. Phenotype
___B___ The trait which is “hidden” in the F1 generation.
E. Gene
___C___ The genetic makeup of an organism (BB, Pp, ff)
F. Allele
___D___ The physical expression of alleles (Brown hair, blue eyes).
2. For each genotype, indicate whether it is heterozygous (HE) or homozygous (HO)
AA ____HO__
ff ___HO___
Bb ____HE__
Gg ____HE__
cc ___HO__
DD ___HO___
Ee ____HE___
HH ___HO__
Ii ___HE___
jj ____HO___
3. For each of the genotypes below, determine the phenotype, using the given information.
Purple flowers are dominant to white flowers Brown eyes are dominant to blue eyes
PP _____Purple___________________
BB ______Brown_________________
Pp _____Purple___________________
Bb ______Brown_________________
pp _____White___________________
bb _______Blue__________________
Green seeds are dominant to yellow
Freckles are dominant to no freckles
GG _____Green___________________
FF ______Freckles_________________
Gg _____Green____________________
Ff ____Freckles____________________
gg ______Yellow__________________
ff ____No freckles____________________
4. For each phenotype, list ALL possible genotypes. (Remember to use the letter of the dominant trait)
Straight hair is dominant to curly hair
Widow’s peak is dominant to normal hairline
____SS or Ss____ Straight hair
_____WW or Ww_____ Widow’s peak
_____ss________ Curly hair
______ww______ Normal hairline
5. Set up the punnett square for each of the crosses listed below. The characteristic being studied is seed
texture - round seeds (dominant) and wrinkled seeds (recessive).
R
Rr x rr
r
r
Rr
rr
r
Rr
rr
What percentage of the offspring
would you expect be round? _50%__
Wrinkled? _50%______
R
r
R
RR
Rr
What percentage of the offspring
would you expect be round? _75%
r
Rr
rr
Wrinkled? __25%
R
R
R
RR
RR
What percentage of the offspring
would you expect be round? _100%_
r
Rr
Rr
Wrinkled? __0%_____
Rr x Rr
RR x Rr
Complete the punnett squares below using the given information.
6. A TT (tall) plant is crossed with a tt (short plant).
t
Which trait is dominant? ________TALL_____________
Give the expected probabilities for each genotype and phenotype.
TT: ___0____%
Tt: ___100____%
t
T
Tt
Tt
T
Tt
Tt
tt: ____0___%
Tall: ___100____% Short: ____0___%
T
t
T
t
TT
Tt
Tt
tt
7. A hybrid tall (Tt) plant is crossed with a hybrid (Tt) plant. Give the
expected probabilities for each genotype & phenotype.
TT: 25%
Tt: 50%
Tall: 75%
Short: 25%
tt:25%
8. A heterozygous round seeded plant (Rr) is crossed with a
homozygous round seeded plant (RR). Give the expected
probabilities for each genotype and phenotype.
RR: 50%
Rr: 50%
Round: 100%
Rr
r
r
R
RR
Rr
R
RR
Rr
rr:0%
Wrinkled: 0%
R
R
r
R
Rr
Rr
9. A homozygous round seeded plant is crossed with a homozygous
wrinkled seeded plant. What are the genotypes of the parents?
Rr
What percentage of the offspring will also be homozygous? ___0__%
_____RR_____ x _____rr_____
p
10. In pea plants purple flowers are dominant to white flowers. If two
white flowered plants are crossed, what percentage of their offspring
will be white flowered? ____100_______%
p
P
p
p
p
Pp
Pp
pp
pp
p
p
pp
pp
pp
pp
11. A white flowered plant is crossed with a plant that is heterozygous
for the trait. What percentage of the offspring will have purple
flowers? ___50______%
P
p
P
PP
Pp
12. Two plants, both heterozygous for the gene that controls flower
color are crossed. Give the expected RATIOS for each genotype and
phenotype.
p
Pp
pp
Phenotype Ratio - ___3_____ : ____1___
Gentoype Ratio S
S
s
SS
Ss
____1____ : ____2____ : _____1___
s
Ss
ss
13. In guinea pigs, the allele for short hair is dominant over long hair.
Two short haired guinea pigs are mated several times. Out of 100
offspring, 25 of them have long hair.
What are the probable genotypes of the parents?
______Ss______ x _____Ss______ (Show the cross to prove it!)
Use the information for SpongeBob’s traits to answer the questions that follow.
14. Everyone in Squidward’s family has light blue skin, which is the
dominant trait for body color in his hometown of Squid Valley. His
family brags that they are a “purebred” line. He recently married a nice b
girl who has light green skin, which is a recessive trait. Create a Punnett
square to show the possibilities that would result if Squidward and his
b
new bride had children.
B
B
Bb
Bb
Bb
Bb
Give the expected RATIOS for each genotype and phenotype.
Phenotype Ratio - ____4__ : __0__
Gentoype Ratio -
____0___ : ___4____ : ____0___
Would Squidward’s children still be considered purebreds? Explain.
No – even though they have blue skin, they are HYBRIDS.
B
b
B
BB
Bb
b
Bb
bb
7. Assume that one of Squidward’s sons married a girl that is
heterozygous for her light blue skin.. Create a Punnett square to show
the possibilities that would result if they had children.
Give the expected RATIOS for each genotype and phenotype.
Phenotype Ratio - ____3____ : ____1____
Gentoype Ratio -
_____1___ : ___2_____ : ____1____
8. Mr. Krabbs and his wife recently had a Lil’ Krabby, but it has not
been a happy occasion for them. Mrs. Krabbs has been upset since she T
first saw her new baby who had short eyeballs. She claims that the
hospital goofed and mixed up her baby with someone else’s baby. Mr.
Krabbs is homozygous for his tall eyeballs, while his wife is heterozygous t
for her tall eyeballs. Some members of her family have short eyes, which
is the recessive trait.
T
T
TT
TT
Tt
Give the expected RATIOS for each genotype and phenotype.
Phenotype Ratio - ____4____ : ____0____
Gentoype Ratio -
____2____ : ____2____ : ____0____
Did the hospital make a mistake? Defend your answer with an explanation.
Yes – There is no possible way for Mr. and Mrs. Krabbs to have a baby with short eyeballs.
Tt