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 flowers
PP ___________________________
Pp ___________________________
pp ___________________________

Brown eyes are dominant to blue eyes
BB ___________________________
Bb ___________________________
bb ___________________________

Round seeds are dominant to wrinkled
RR ___________________________
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 bDominant Recessive
Ear Lobes-or-Attached Ear Lobes E eDominant Recessive
Widow’s Peak-or-Straight Hairline W wDominant Recessive
Dimples (2 dimples or1 dimple)-or-No Dimples D dDominant Recessive
Bent Back Thumb-or-Straight Thumb T tDominantRecessive
Dark Hair-or-Light Hair H hDominant Recessive
Can Roll Tongue-or-Cannot Roll Tongue R rDominant Recessive
Bent Pinky-or-Straight Pinky P pDominant Recessive

  After you have collected all the data and created a table, create agraph that represents all of your collected data. Remember, you can choose from the following graphs:? bar graph,? circle graph,? line graph,? line plot, or? Scatter plot.Be sure to label your graph properly. Now it is time to analyze the data you have collected. Using your knowledgeof Punnett Squares, you will make some predictions based on your calculations.  Print and then complete Worksheet 1 Worksheet 1NAME:__________________________________DATE:___________Use the data you have collected to answer the followingquestions.1. Create a tree diagram that illustrates the number of possible combinations of the following traits: non-blue/blue eyes, can roll tongue/cannot roll tongue, and dark hair/light hair. Using the Fundamental Counting Principle, how many differentcombinations should you come up with? 2. What is the probability that one of your peers would have all of the following characteristics: dimples, bent pinky, and attached ear lobes? What is the probability of each characteristic separately? For example, what is the probability of one of your peers having dimples? Assume that it is equally likely to have each trait. 3. What is the probability that someone in your classroom will have all of the dominant traits? All of the recessive traits? 4. If you were to use the data you collected from your classmates as a sample, what percent of your school would have no dimples? Bent thumb? Widow’s peak? 5. Now that you have answered a few questions, find the total number of students in your grade. Set up a ratio, and predict the number of people that will have the following characteristics:Blue eyes, Unattached ear lobes, Straight hair line, Dimples, Straight thumb, andLight hair. To answer the following questions, work with a partner. Using the individual data about yourself, determine the probability of a child resulting from a cross of your 6 traits.  Set up a Punnett Square, and fill it in for eye color. What is the probability that a child resulting from a cross of your genetic traits would have blue eyes  Set up a Punnett Square, and fill it in for hair color. What is the probability that a child resulting from a cross of your genetic traits would have dark hair?  Set up a Punnett Square for the ability to roll your tongue. What is the probability that a child resulting from a cross of your genetic traits could not roll their tongue?  Set up a Punnett Square for bent/straight pinky and widow’s peak/straight hairline. What is the probability that a child resulting from a cross of your genetic traits would have a straight pinky and a widow’s peak? Set up a Punnett Square for unattached/attached ear lobes andbent back thumb/straight thumb. What is the probability that a child resulting from a cross of your genetic traits would haveunattached ear lobes and a bent back thumb?

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

Links

Genetics tutorials can be found at this website http://www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/monohybrid_cross.html