# Genotypic and Phenotypic Probabilities

Course Outline

A.   Punnett Squares

1.    Punnet Square-monohybrid cross

2.   Punnet square-dihybrid cross

B.   Probability

Teaching Aids

1.  Computer

2.  Smart Board

3.  Powerpoint

4.  The following worksheet will be given for homework.  The teacher will go over the answers with the students the next day.

## Simple Genetics Practice Problems

Name__________________________

1. For each genotype, indicate whether it is heterozygous (HE) or homozygous (HO)

 AA ____Bb ____Cc ____Dd ____ Ee ____ff ____GG ____ HH ____ Ii ____Jj ____kk ____Ll ____ Mm ____nn ____OO ____Pp

2. For each of the genotypes below, determine the phenotype.

 Purple flowers are dominant to white flowersPP ___________________________Pp ___________________________pp ___________________________ Brown eyes are dominant to blue eyesBB ___________________________Bb ___________________________bb ___________________________ Round seeds are dominant to wrinkledRR ___________________________Rr ___________________________rr ___________________________ Bobtails are recessive (long tails dominant)TT ___________________________Tt ___________________________tt ___________________________

3. For each phenotype, list the genotypes. (Remember to use the letter of the dominant trait)

 Straight hair is dominant to curly.____________ straight____________ straight____________ curly Pointed heads are dominant to round heads.____________ pointed____________ pointed____________ round

4. Set up the square for each of the crosses listed below. The trait being studied is round seeds (dominant) and wrinkled seeds (recessive)

 Rr x rr What percentage of the offspring will be round? ___________ Rr x Rr What percentage of the offspring will be round? ___________ RR x Rr What percentage of the offspring will be round? ___________

Practice with Crosses. Show all work!

5. A TT (tall) plant is crossed with a tt (short plant).
What percentage of the offspring will be tall? ___________

6. A Tt plant is crossed with a Tt plant. What percentage
of the offspring will be short? ______

7. A heterozygous round seeded plant (Rr) is crossed with a
homozygous round seeded plant (RR). What percentage of
the offspring will be homozygous (RR)? ____________

8. A homozygous round seeded plant is crossed with a homozygous
wrinkled seeded plant. What are the genotypes of the parents?
__________ x __________

What percentage of the offspring will also be homozygous? ______________

9. In pea plants purple flowers are dominant to white flowers.
If two white flowered plants are cross, what percentage of their
offspring will be white flowered? ______________

10. A white flowered plant is crossed with a plant that is
heterozygous for the trait. What percentage of the
offspring will have purple flowers? _____________

11. Two plants, both heterozygous for the gene that controls
flower color are crossed. What percentage of their offspring
will have purple flowers? ______________
What percentage will have white flowers? ___________

12. In guinea pigs, the allele for short hair is dominant.
What genotype would a heterozygous short haired guinea pig have? _______
What genotype would a purebreeding short haired guinea pig have? _______
What genotype would a long haired guinea pig have? ________

13. Show the cross for a pure breeding short haired guinea pig
and a long haired guinea pig.
What percentage of the offspring will have short hair? __________

14. Show the cross for two heterozygous guinea pigs.
What percentage of the offspring will have short hair? ________
What percentage of the offspring will have long hair? _______

15. 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? ________ x ___________ Show the cross to prove it!

Class Projects

Punnett Square ProjectYou will be collecting and recording some specific genetics-related information about the students in your class.  You will then analyze and calculate different statistics based on your data. Next you will analyze a given couple and answer questions about their potential offspring. Collect DataListed below are eight different pairs of traits. One trait will be labeled D for dominant, and one will be labeled R for recessive. It is your job to consult with eachperson in your class and find out which traits they have. Once you have tallied up the different traits, create a table that displays all of your collected data. Trait                                         Symbol                           Dominant or Recessive
 Non-blue eyes-or-Blue eyes B b Dominant Recessive Ear Lobes-or-Attached Ear Lobes E e Dominant Recessive Widow’s Peak-or-Straight Hairline W w Dominant Recessive Dimples (2 dimples or1 dimple)-or-No Dimples D d Dominant Recessive Bent Back Thumb-or-Straight Thumb T t DominantRecessive Dark Hair-or-Light Hair H h Dominant Recessive Can Roll Tongue-or-Cannot Roll Tongue R r Dominant Recessive Bent Pinky-or-Straight Pinky P p Dominant Recessive

Review Questions

1.  If a black guinea pig (Bb) were crossed with a white guinea pig (bb) what would be the resulting phenotypic ratio?

a.  0:1 black to white                               b.  1:0 black to white

c.  1:1 black to white                               d.  3:1 black to white

2.  In garden peas, purple flowers (P) are dominant to white (p) flowers, and tall plants (T) are dominant to short plants (t).  If a purple tall plant (PpTt) is crossed with a white short plant (pptt), what is the resulting phenotypic ratio?

a.  1:1:1:1 purple tall to purple short to white tall to white short

b.  3:2 purple tall to purple short

c.  9:3:3:1 purple tall to purple short to white tall to white short

d.  all purple tall