NAME: _____________________________________
Mendelian Genetics – Examining Probability
When we study heredity, one thing we are looking at is the probability that a particular chromosome will be
passed on, through the egg or sperm, to the offspring. As you know, genes and chromosomes are present in pairs
in the body cells of every organism, and those pairs separate as the cells go on to form gametes (eggs and sperm).
There are two possible genes that may wind up in a sperm or egg, but they actually only receive one of them due
to meiosis. If the probability of the sperm or egg getting either gene after meiosis is equal, then we can express
this probability as 1:2 or ½. This is like the probability of getting heads or tails when you flip a coin.
In this lab, you will work with your partner to see if Mendel’s “F2 generation” results make sense. You will each
represent one heterozygous parent. As a heterozygous parent you are carrying two different alleles. This means
you have a 1:2 (50/50) chance of passing on one allele or the other to you offspring. You will flip the coin to
determine which allele you pass on to your offspring. Your partner will do the same.
If you flip a Heads you passed on the dominant allele. If you flip a tails you passed on the recessive allele.
SO… if you and your partner both flip heads the genotype of the offspring is _____________________
If you and your partner both flip tails, the genotype of the offspring is ___________________________
And is one of you flips heads but the other flips tails, the genotype of the offspring is ______________
You will toss the coins 100 times each. In the data table below, record the genotype of the offspring
produced from each flip.
Toss
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Genotype
Toss
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Genotype
Toss
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Genotype
Toss
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
Genotype
Toss
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
Genotype
NAME: _____________________________________
Analysis:
Look at Mendel’s results. What probability did he find for each of the genotypes when two heterozygous
parents were crossed? Compare this with your results. Tally up how many of your 100 offspring received
each of the three genotypes. Record your answers in the data table below.
Genotype
Expected Results (based on
Mendel’s research)
Out of 100
Actual Results (based on your
data table)
Out of 100
Homozygous Dominant
Heterozygous
Homozygous Recessive
1. Draw a Punnett Square to illustrate two heterozygous parents.
2. What are the possible genotypes that may result from the cross of two heterozygous parents?
3. What is the ratio of those genotypes?
Assume that your Punnett square is for flower color, with purple flowers being dominant to white.
4. What are the possible phenotypes that may result from the cross of two heterozygous parents?
5. What is the ratio of those phenotypes?
6. How close did your actual results come to what Mendel predicted?