Name:
Per:
Date:
Genetics Notes: Incomplete Dominance and Co-dominance
Incomplete Dominance means that one allele is NOT fully dominant over
the other in a ______________________________ individual.
In Incomplete Dominance, the new phenotype is an intermediate _________
between the two homozygotes.
An example of incomplete dominance would be when ______ flowering plants
crossed with ________ flowering plants yield _______ flowering offspring.
F1 hybrids have an appearance somewhat ____-_________ the phenotypes
of the two parental varieties. Looks _________________
Example 1: snapdragons (flower)
________ = red flower
________ = white flower
P1 gen: RR (Red) x WW (white)
R
R
Genotype:
W
Genotypic ratio:
Phenotype:
W
Phenotypic ratio:
Example 2: In cattle, longhorns are incompletely dominant to shorthorns.
A heterozygous individual would have ___________ horns. Cross a longhorn
bull & a shorthorn cow. Give the genotypes & phenotypes (with ratios) of the
offspring.
______=longhorn, ______=shorthorn, ______=medium horn
P1 gen: ______(longhorn) x ______ (shorthorn)
____ ____
Genotype:
Genotypic ratio:
Phenotype:
Phenotypic ratio:
Example 3: The Panola petunia is a flower that shows incomplete dominance.
Red flowers have a genotype of ______, white flowers of ______, and pink
flowers of ______. In a flower show, the following results were obtained:
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48 red flowers and 52 pink flowers. What were the probable genotypes
of the parent flower plants? Explain.
____
____
Parent Genotypes: ______ x ______
** 48 and 52 are real close to 50/ 50; place the resulting offspring from the
problem in the box and work backwards to find the parent’s genotypes
Example 4: The color of fruit for plant "X" is determined by two alleles.
When two plants with orange fruits are crossed, the following phenotypic
ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25%
yellow fruit. What are the genotypes of the parent orange-fruited plants?
F1 gen: ______ (orange) x ______ (orange)
____ ____
______ = Red fruit
______= Orange fruit
______ = Yellow fruit
Co-dominance
____-____________________ means that one allele is not fully dominant
over the other in a heterozygous individual.
In such cases, the heterozygous phenotype does not look like either
homozygous phenotype.
Instead, the two contrasting alleles are both ________________to
produce a new phenotype.
Both alleles are ___________________in the heterozygous individual.
An example of co-dominance would be when a red-flowered plant is crossed
to a white- flowered plant yielding a _______________ flowered offspring
(showing both red & white colors; it does NOT look _______________).
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Practice 1: ______= red
_______= roan
______= white
Cross a white bull with a red cow. Is it possible to obtain white offspring?
P1 gen: ______ (White) x ______ (Red)
Answer:
Practice 2: In Tupelo chickens, the alleles for feather color are black (B)
and white (W). These two alleles are co-dominant. When both alleles are
present, the resulting birds have both black feathers and white feathers,
giving it a “_____________” appearance. Cross a checked rooster with a
checked hen.
P1 gen: ______ (checked) x ______ (checked)
Genotypes:
Genotypic ratio:
Phenotypes:
Phenotypic ratio:
___-____________________ means both alleles are expressed equally.
______________________________ is caused by co-dominant alleles
Affects 1 out of 500 African Americans
Sickle cell disease is characterized by the _______________________
shape of the red blood cells (rbc); they look like sickles
Deformed rbc tend to _______________________________________
(narrowest blood vessels) and _________________________________,
damaging tissues and organs
This disease is sometimes fatal, and is very painful.
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____________________ is a protein in rbc that carries O2, and ____
change in the hemoglobin gene causes sickle cell disease.
Why do so many African Americans carry this sickle cell allele?
People ___________________ for this allele have higher protection
against Malaria, a disease prevalent in West Africa.
Sickle-Cell Disease Practice 3:
______ = Normal Red Blood Cells
______ = Mild sickle-cell disease
______-= Sickle-shaped Red Blood Cells
Practice 3:
Cross two people who are heterozygous for Sickle-Cell Disease
P1 Generation: _____
x _____
Genotypes: ____, ____, ____
Genotypic ratio: __________
Phenotypes:__________________,
___________________________,
____________________________
Phenotypic ratio: __________
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