Biology 12

376 MHR • Unit 4 Evolution

For your Unit Project on Searching for a Common

Ancestor, consider how new techniques in DNA analysis

can help determine relatedness among fossils. How

would evolving populations of possible ancestral fossils

differ from the Hardy-Weinberg principle?

UNIT PROJECT PREP

http://www.mcgrawhill.ca/links/biology12

One application of the Hardy-Weinberg equation is to predict

how many people in one generation of a human population are

carriers of a particular recessive allele. If the number of babies

born annually with a particular disease (such as phenylketonuria

[PKU] or cystic fibrosis) are known, the number of adults that

carry the allele can be predicted. This information can be used

to track trends in the conditions, help medical researchers

garner support for their work, and help public-health workers

allocate their time and resources effectively. To learn more

about these diseases and the frequency of these recessive

alleles in our population, go to the web site above, and click on

Web Links. Determine the frequency of the recessive traits for

PKU and cystic fibrosis using the Hardy-Weinberg equation.

WEB LINK

Practice Problems

1.An investigator has determined that 16 percent

of a certain human population cannotroll

their tongue. The ability to roll the tongue

is controlled by a dominant allele. Calculate

the genotype and allele frequencies for the

population.

2.In a certain population, 30 percent are

homozygous dominant, 49 percent are

heterozygous, and 21 percent are homozygous

recessive. What percentage of the next

generation is predicted to be homozygous

recessive, assuming a Hardy-Weinberg

equilibrium?

3.In a population of pea plants, 1 percent are

short, which means they are homozygous

recessive. What are the frequencies of the

recessive allele t and the dominant allele T?

What are the genotypic frequencies in this

population?

SECTION REVIEW

1. The Hardy-Weinberg principle is a model that
   uses a hypothetical situation that would rarely, if ever,
   be replicated in nature. Explain why it is useful to use
   the Hardy-Weinberg principle to help understand
   population genetics.


2. A biologist has found that 10 percent of a
   population of bats are hairless, which is a recessive
   trait. Assuming that the population is in Hardy-
   Weinberg equilibrium, determine the genetic structure
   (genotype and allele frequencies) of the population.


3. List the conditions necessary to maintain the
   Hardy-Weinberg equilibrium.


4. Select one condition that is necessary for the
   Hardy-Weinberg equation to work, and explain why
   this condition must be met for no change to occur.


5. A population of flowers are in Hardy-Weinberg
   equilibrium with 32 white flowers and 168 yellow
   flowers. The white flowers are bb and the yellow
   flowers are Bb or BB, where b is recessive and B is

dominant. Draw a table showing the phenotypes,

genotypes, frequency of the genotypes in the

population, and frequency of alleles B and b. Create

a Punnett square that shows the potential crosses for

this population of flowers.

6. If a plant breeder started selecting either the
   white or the yellow flowers from Question 5 above,
   would the population be in Hardy-Weinberg
   equilibrium?


7. Is the human population of North America in
   Hardy-Weinberg equilibrium? Explain your answer.


8. Why would you expect the whooping crane
   population of North America to not be in Hardy-
   Weinberg equilibrium?

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