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Guided Inquiry • Skills Lab
Additional Lab 7
Independent Assortment and
Gene Linkage
Problem
How do the positions of genes on chromosomes affect patterns of inheritance?
Introduction
Most of your cells contain 23 pairs of homologous chromosomes. The homologous
chromosomes are not identical because one chromosome came from your mother and
one from your father. Each may contain different versions, or alleles, of its genes.
The interaction of these alleles determines your phenotype.
During mitosis, each daughter cell receives 23 pairs of chromosomes identical to
the parent cell. But during meiosis, when cells form gametes, each daughter cell
receives only one chromosome from each homologous pair. Thus, a gamete has just
one allele for each gene. The positions of genes on chromosomes and the movements
of chromosomes during meiosis affect patterns of inheritance.
In this lab, you will explore different inheritance patterns of two traits in an
imaginary animal, the flightless knot-bird.
Skills Focus
Use Models, Analyze Data, Draw Conclusions
Pre-Lab Questions
1. Infer What are the possible genotypes for a knot-bird with straight ears? For a
bird with webbed feet?
2. Apply Concepts Use the Punnett square below to show how the alleles for ear
shape will be inherited if a pair of heterozygous straight-eared birds mate.
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3. Calculate What fraction of the offspring from the cross in
Question 2 would you expect to have straight ears?
4. Form a Hypothesis How will the location of genes affect the inheritance
patterns of genes?
Procedure
Individual knot-birds can have straight or curly ears, and feet that are webbed or
have free toes. The ear and feet phenotypes are each determined by a single
gene with a dominant and a recessive allele.
Alleles in Knot-Birds
Dominant Alleles
Recessive Alleles
E = straight ears
e = curly ears
F = free toes
f = webbed feet
Part A: Inheritance of Genes on Different Chromosomes
A single pair of knot-birds—a male with straight ears and free toes, and a
female with curly ears and webbed feet—is bred. The male is heterozygous for
both traits. For Part A, assume the genes for ears and feet are on different
chromosomes.
1. Identify each adult bird in Figure 1 as male or female and record its
genotype for ears and feet.
Figure 1 Adult knot-birds
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2. Use the space below to show four ways the alleles for ears and feet could be
combined in the male knot-bird’s gametes when the genes are on different
chromosomes. Draw a circle for each gamete, and use letters to represent the
alleles.
3. How will the alleles be combined in the female knot-bird’s gametes? Record your
answer in the first column of the Punnett square in Figure 2.
4. Transfer the data from Step 2 to the first row in Figure 2, one arrangement per
column.
5. Record the genotype of each baby knot-bird on the line provided and complete
the sketch of each bird’s phenotype.
Figure 2 Possible offspring from knot-bird cross when genes are on different chromosomes
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Part B: Inheritance of Genes on the Same Chromosome
For Part B, assume that the genes for ears and feet are on the same chromosome.
Also assume that on one of the male’s homologous chromosomes the alleles are
Ef, and on the other they are eF.
6. Use the space below to show two ways the alleles could be combined in the
male knot-bird’s gametes when the genes are on the same chromosome.
Draw a circle for each gamete, and use letters to represent the alleles.
7. How will the alleles be combined in the female knot-bird’s gametes?
Record your answer in the first column of the Punnett Square in Figure 3.
8. Transfer the data from Step 6 to the first row in Figure 3, one arrangement
per column.
9. Record the genotype of each baby knot-bird on the line provided, and
complete the sketch of each bird’s phenotype.
Figure 3 Possible offspring from knot-bird cross when genes are on the same
chromosome
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Analyze and Conclude
1. Use Models What principle was modeled in Part A? What principle was
modeled in Part B?
2. Draw Conclusions What effect did moving the genes to the same chromosome
have on the male bird’s gametes?
3. Compare and Contrast Did moving the genes to the same chromosome have
the same effect on the female bird’s gametes? Why or why not?
4. Apply Concepts Fill in the Punnett square to illustrate the cross of a pair of
knot-birds who both have the genotype EeFf. Assume the genes are on different
chromosomes. Then, describe the phenotypes that will appear in the offspring
and the percentage of offspring with each phenotype.
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5. Apply Concepts Use the Punnett square to determine how the results
change for the cross described in Question 4 when the genes are on the
same chromosome. Assume that the linked combinations are EF and ef for
both the mother and father. Describe the phenotypes that will appear in the
offspring and the percentage of offspring that will have each phenotype.
6. Infer The inheritance pattern you found in Question 5 persists for several
generations. What does that tell you about the relative positions of the genes
for ear and foot appearance on their chromosome?
Extend Your Inquiry
Suppose you cross a male with straight ears and webbed feet with a female
that has curly ears and free toes. Four different phenotypes show up among
their offspring: straight ears with webbed feet, straight ears with free toes,
curly ears with webbed feet, and curly ears with free toes. What is the
genotype of each parent? Explain your answer.
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