SAMPLE RESPONSES 1. Genotype refers to the set of alleles

SAMPLE RESPONSES 1. Genotype refers to the set of alleles

GENES AND TRAITS • ACTIVITY 5
SAMPLE RESPONSES
1. Genotype refers to the set of alleles
that an organism inherits. Phenotype refers to the traits exhibited
by the organism based on the
alleles (genotype) it has inherited.
For example, a corn kernel that is
heterozygous for corn color has a
genotype of Pp and a phenotype
of purple kernels.
2. Simple dominance occurs when, of
two possible traits, one is recessive
and one is dominant. A heterozygous individual will have the phenotype of the dominant trait.
Incomplete dominance is different
in that neither trait is dominant. If
an organism is heterozygous, the
trait will be a blend of or intermediate between the two. In codominance a heterozygous organism will
express the phenotype of both
traits.
3. In most cases, both phenotype and
genotype are altered. A new gene is
inserted, which changes the corn’s
genotype, and the insertion of the
gene causes a change in a trait,
which is an organism’s phenotype.
Thus, both the Bt corn’s phenotype and genotype were altered.
GENES AND TRAITS • ACTIVITY 5
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3. Think back to the Bt corn you considered in Activity 1, “A Genetically Modified Solution?” When an organism is genetically modified, which of the following is changed: genotype, phenotype, both, or neither? Explain.
4. The following is a list of a few traits in plants and animals. Determine if the
traits described are examples of simple dominance, codominance, or incomplete dominance. Explain your reasoning.
Trait
Description
Feather color
in chickens
The feathers of a species of chicken
can be black, white, or “erminette.”
Erminette chickens have both black
feathers and white feathers, but not
gray feathers.
Sweet pea
tendrils
When sweet pea plants with tendrils
(structures that grow from the
stem and help the plant attach and
climb) are crossed with sweet pea
plants without tendrils, all of the
resulting sweet peas have tendrils.
Rabbit hair
length
Longhaired rabbits crossed with
shorthaired rabbits produce offspring that have medium-length hair.
KEY VOCABULARY
allele
homozygous
codominance
incomplete dominance
dominant
phenotype
gamete
Punnett square
gene
recessive
genotype
selective breeding
heredity
trait
heterozygous
Sample Student Response to Analysis Question 4
Trait
Description
Type of dominance
and reasoning
Feather color
in chickens
The feathers of a species of
chicken can be black, white, or
erminette. Erminette chickens have
both black feathers and white
feathers, but not gray feathers.
Codominance because both traits
are expressed (feathers are white
and black), and they do not blend
as they would with incomplete
dominance (no gray feathers)
Sweet pea
tendrils
When sweet pea plants with
tendrils (structures that grow from
the stem and help the plant attach
and climb) are crossed with sweet
pea plants without tendrils, all
of the resulting sweet peas have
tendrils.
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Simple dominance because
the
dominant trait (tendrils) masks the
recessive trait (no tendrils)
Rabbit hair
length
Longhaired rabbits crossed with
shorthaired rabbits produce
offspring that have mediumlength hair.
Incomplete dominance because
the offspring have medium-length
hair which is a blend of the two
traits (long and short)
4. Samples of students’ answers are
shown at right in the third column.
REVISIT THE CHALLENGE
Type of dominance and reasoning
Students should be able to articulate that
observing the traits of offspring over
­multiple generations provides information
about the genetic makeup of parents and shows how those
specific traits are inherited. Students modeled this process in
Activity 4, “Breeding Corn,” when they counted the corn
­kernels by color and with that determined the genotype of
the parent corn. Mendel used this same process to propose
the fundamental rules of heredity, which explain how traits
are passed from one generation to the next. Students should
also be able to explain that not all traits are simply dominant
and recessive, and that other patterns, such as codominance
and incomplete dominance, are exhibited with many traits.
Emphasize that most traits are influenced by multiple genes
and by environmental factors.
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