Roger Rabbit's Family --- A Study of Population
Genetics
Image: http://www.cs.newcastle.edu
Introduction:
Roger Rabbit and his family have lived in Toontown for quite a while. Roger
himself settled down and married a cute little bunny named Rita Rabbit, and they have
added on to their hutch several times making room for all of their new little bunnies. On
special occasions whenever the Rabbit family gets together, Roger Rabbit has
grandparents, great grandparents, aunts and uncles, and more cousins than he can
count to visit and munch carrots with.
Recently at the Rabbit family reunion, Roger noticed that there were two fur
colors in the Rabbit clan --- those with brown colored fur and those with albino (white)
fur like Roger. These phenotypes had been recorded over several generations in the
Rabbit family pedigree. The pedigree showed that two albino rabbits could only have
albino offspring, while two brown rabbits or one brown rabbit could have both brown and
albino bunny offspring.
The number and frequency of a particular gene or allele in a population is known
as the frequency of that allele and is usually expressed as a percent or decimal. In
stable environmental conditions, the frequency of alleles for a trait in a genetically
balanced population that mates randomly tends to remain the same. Thus, if the
environment doesn't change, the frequency of the alleles for either albino or brown fur
should remain the same. The maintenance of gene or allele frequencies in populations
is known as the Hardy-Weinberg principle.
Objective:
Students will determine the frequency of alleles in a population through the use of the
Hardy-Weinberg principle.
Materials:



Paper
Pencil
Calculator
Procedure (Part A) – Counting Alleles:
1. Let B stand for the dominant allele (brown fur color) and b stand for the recessive
allele (albino or white fur).
2. Rabbits with the genotype BB or Bb will have brown fur and those with the
genotype bb will have albino fur.
3. Table 1 has the genotypes of 200 rabbits from the Roger Rabbit family. To
determine the frequency of these alleles in the Roger Rabbit population, count
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the total number of alleles or genes, the number of B alleles, and the number of
b alleles. Record these numbers in Table 2.
Table 1
Genotypes for 200 Roger Rabbit Family Members
bb
BB
bb
BB
Bb
bb
BB
bb
Bb
bb
Bb
bb
bb
BB
bb
bb
BB
bb
bb
Bb
bb
Bb
bb
bb
bb
Bb
bb
Bb
bb
bb
Bb
Bb
BB
bb
bb
Bb
bb
Bb
bb
bb
Bb
bb
bb
Bb
bb
Bb
bb
Bb
bb
Bb
Bb
Bb
Bb
bb
BB
Bb
Bb
bb
Bb
bb
bb
bb
bb
Bb
bb
bb
Bb
bb
Bb
bb
bb
Bb
bb
bb
Bb
BB
bb
bb
bb
Bb
Bb
bb
BB
bb
Bb
bb
bb
Bb
bb
bb
Bb
Bb
bb
Bb
BB
bb
Bb
bb
Bb
bb
Bb
bb
Bb
bb
bb
Bb
bb
Bb
bb
bb
Bb
bb
Bb
bb
bb
bb
BB
bb
Bb
Bb
Bb
Bb
bb
BB
Bb
bb
Bb
bb
Bb
bb
Bb
bb
Bb
bb
Bb
Bb
Bb
Bb
bb
Bb
BB
Bb
Bb
bb
Bb
bb
Bb
bb
Bb
bb
Bb
bb
Bb
Bb
bb
Bb
bb
Bb
BB
bb
Bb
bb
Bb
bb
Bb
bb
Bb
Bb
Bb
bb
bb
Bb
Bb
bb
Bb
bb
BB
Bb
bb
Bb
bb
bb
Bb
bb
Bb
Bb
bb
Bb
Bb
bb
bb
bb
bb
bb
BB
bb
Bb
Bb
BB
BB
Table 2
Total Number of Alleles
(B + b)
Total Number of B
Alleles
Total Number of b
Alleles
Procedure (Part B) – Determining Allele Frequency:
1. Use the following formulas to calculate the allele frequency of recessive allele b
and dominant allele B. Make sure your answer is in the form of a decimal.
Frequency of b =
Number of b alleles
2
Total # of alleles (B+b)
Frequency of b =
Frequency of B =
Frequency of B =
_____________ (answer)
Number of B alleles
Total # of alleles (B+b)
_____________ (answer)
2. To check to see if you have done your calculations correctly, the sum of the two
frequencies should be 1.0 or 100 percent. In the Hardy-Weinberg equations, the
frequency of the dominant allele in a population is designated p, and the
frequency of the recessive allele is designated as q. Use the following equation
to check your answer.
p + q = 1.0 (100 per cent)
Procedure (Part C) – Comparing Allele frequencies and Phenotypic
Frequencies:
1. Determine the frequency of albino rabbits in the population by dividing the
number of albino rabbits (bb) by the total number of rabbits (200). write your
answer as a decimal.
Frequency of albino rabbits = Number of albino rabbits (bb)
total number of rabbits (200)
Frequency of albino rabbits = ___________
How does this compare to the frequency of the recessive allele b (larger, smaller,
the same)?
___________________________________
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2. The frequency of albino rabbits in a population is equal to q2. Look at the
frequency of allele b on Procedure B. The value you determined was q in the
Hardy-Weinberg equation. Take the square of this number, q2, to determine the
frequency of the homozygous recessive genotype (bb).
q2 = _________
Procedure (Part D) – Determining Other Genotypic Frequencies:
1. The frequency of each possible genotype, homozygous dominant (BB) is
designated by p2, the homozygous recessive genotype (bb) is designated by q2,
and the heterozygous genotype (Bb) is designated by 2pq in the second HardyWeinberg equation. The total of these three genotypic frequencies should also
equal 1.0.
p2
+
2pq
+
q2
=
1.0
2. Use the equation above to calculate the frequency of the homozygous dominant
genotype (p2) for this trait in the rabbit population. Show your work.
3. Use the equation above to calculate the frequency of the heterozygous genotype
(2pq ) for this trait in the rabbit population. Show your work.
Questions:
1. In a population of 200 mice, 8 have short tails, which is a recessive trait. The
other mice have long tails. Determine the frequencies of the genotypes and of
the dominant and recessive alleles.
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2. In this same population, what would be the frequency of the mating between
homozygous dominant males and homozygous recessive females.
3. The cross 2pq x 2pq represents the mating of what two types of individuals.
Extension:
Go online to the activity, “Flashy Fish.”
http://www.pbs.org/wgbh/evolution/educators/lessons/lesson4/act2.html
The activity introduces Professor John Endler who traveled to Trinidad in the 1970’s to
study wild guppies. The guppies live in small streams that flow down the mountains
from pool to pool. In the activity, you will take part in an online simulation of Endler's
work. You will collect data, formulate a hypothesis, and run a series of experiments. You
will find out about the interplay between natural selection and sexual selection in this
wild population of guppies
.
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