U. Probability Practice
Name_________________
Date________
Period____
Standards:
 BI2. c. Students know how random chromosome segregation explains the
probability that a particular allele will be in a gamete.
 BI2. g. Students know how to predict possible combinations of alleles in a zygote
from the genetic makeup of the parents.
 BI3. a. Students know how to predict the probable outcome of phenotypes in a
genetic cross from the genotypes of the parents and mode of inheritance
(autosomal or X-linked, dominant or recessive)
Directions: You will use labeled coins to show how alleles are passed from parents to
offspring and gain a better understanding of the probability of specific allele
combinations. Each coin represents the allele combinations provided by each parent.
Procedure:
1.) Examine the coins. The father’s allele combinations are represented by the front
and back sides of the coin with the black writing. The mother’s allele
combinations are represented by the front and back sides of the coin with the red
writing. Record the allele combination of the gametes of the mother and father
below.
Father Allele Combination in Gametes__________
Mother Allele Combination in Gametes__________
2.) Identify which allele is dominant and which allele is recessive below.
A=_____________
a=_____________
3.) Flip the coins representing each gamete’s allele combination. The two coins
(alleles) together make up the genotype of the offspring since the offspring get
one set of genetic information from their mother and one set from their father.
Record the genotype of the offspring in the table below. Repeat step three, 49
more times.
Table 1: Genotypes of Offspring
1.)
2.)
3.)
4.)
5.)
6.)
7.)
8.)
9.)
10.)
11.)
12.)
13.)
14.)
15.)
16.)
17.)
18.)
19.)
20.)
21.)
22.)
23.)
24.)
25.)
26.)
27.)
28.)
29.)
30.)
31.)
32.)
33.)
34.)
35.)
36.)
37.)
38.)
39.)
40.)
41.)
42.)
43.)
44.)
45.)
46.)
47.)
48.)
49.)
50.)
Totals for Aa__________
Totals for aa___________
4.) Calculate the probability of the offspring having each genotype.
Aa =________%
aa=_________%
5.) Set up a ratio to explain the occurrence of dominant and recessive phenotypes in
the offspring.
Follow-up Questions:
1.) Did the genotype produced during any one trial depend upon the results of
another?
2.) What is the relationship between genotypes and phenotypes?
3.) What happens to the phenotype of an organism when one dominant allele is
present?
4.) What happens to phenotype of an organism if it has homozygous recessive (two
small letters)?
5.) What is probability?
6.) How does meiosis provide the alleles for the gametes?
7.) How many alleles for each trait do the parents contribute?