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1. Cross a heterozygous man for eyebrows with
a woman with a unibrow. A unibrow is a
recessive trait.
1. What are the chances of them having a child
with a unibrow?
Special Crosses: Incomplete
Dominance and Codominance
What is Incomplete
Dominance?
• Blending of the dominant and
recessive alleles in
heterozygous
• 3rd phenotype
Plant: Snapdragons
Red: R
White: r
Pink: Rr
Humans: Hair Type
Curly: C
Straight: c
Wavy: Cc
In snapdragons, red flowers are dominant over white
flowers. The heterozygous genotype has pink flowers.
Cross a homozygous red-flowered plant with a pink
flowered plant. What are the chances of producing
white flowers? (R = red and r = white)
If a yellow guinea pig is crossed with a white one, the
offspring are cream-colored. What kinds of offspring
are expected if two cream-colored guinea pig mate?
(Y = yellow and y = white)
What is Codominance?
• Both dominant and
recessive alleles are
expressed in heterozygous
• 3rd phenotype
Chickens: Feather Color
Black: B
White: b
Black and White: Bb
Cattle: Fur Color
Red: R
White: r
Roan: Rr
In certain cattle, hair color can be red (homozygous
RR), white (homozygous rr), or roan (a mixture of red
and white hairs, heterozygous Rr). When a red bull is
mated to a white cow, what genotypes and
phenotypes of offspring could be obtained?
If one of the offspring found above were mated to a
white cow, what genotypes and phenotypes of
offspring could be produced? In what proportion?
Class Data: Fingerprints
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