Download Dominance Relationships

Dominance
Relationships
Recap
•What is genotype and phenotype again?
• So …
• If you show the
dominant phenotype,
what could your
genotype be?
 If you are unsure if the organism is a pure-
bred, you can do a Test Cross
• Test Cross: Cross the
individual that shows
dominant phenotype with a
recessive individual
• If offspring 100% dominant
• Original was pure (HD)
• If offspring not 100%
dominant
• Original was heterozygous
Predicting a Test Cross
Remember, Punnett Squares are usually good
only for single-gene traits.
A
a
A
AA
Aa
a
Aa
aa
Looking at just one trait is
called a MONOHYBRID Cross

Looking at TWO traits in one Punnett Square is called a
DIHYBRID Cross

TRY A DIHYBRID CROSS!
• Show the probabilities of a cross between two people,
both heterozygous Full Lips (Ff), Clefted Chin (Cc)!
• F = Full Lips (dominant), f = Thin Lips (recessive)
• C = Cleft Chin (dominant), c = Non-clefted Chin
• The hardest part is segregating the alleles
• Start with FfCc X FfCc … Go!

FfCc X FfCc
Ff Cc
FC
FC
Fc
fC
FFCC
Ff Cc
(full lips, cleft chin)
Finish Up!
fc

Numbers:
9/16
• How many Full Lips/Clefted Chins? _____
3/16
• How many Thin Lips/Clefted Chins? _____
3/16
• How many Full Lips/Non-clefted? _____
1/16
• How many Thin Lips/Non-clefted? _____
• So, what’s your HomD:Het:Het:HomR ratio?
9 3 3 1
___:___:___:___
9:3:3:1 -This is the classic ratio for a heterozygous dihybrid
cross!

Dominance Relationships
• Complete dominance: one allele shows full dominance
over the other (dominant v. recessive)
• Incomplete dominance: neither allele is fully dominant
over the other (mixed phenotype)
• Codominance: Both alleles dominant; one phenotype
“wins” (shows) in some cells, the other shows in other
cells (either can show)
Which Is This

• Complete Dominance
• Incomplete Dominance
• Codominance
Which Is This
• Complete Dominance

• Incomplete Dominance
• Codominance
Which Is This
• Complete Dominance

• Incomplete Dominance
(Though darker colors tend to show more
strongly than lighter colors)
• Codominance
Which Is This
• Complete Dominance
• Incomplete Dominance

• Codominance
Incomplete Dominance
• In northeast Kansas there is a creature know as a
wildcat. It comes in three colors, blue, red, and purple.
This trait is controlled by a single gene with incomplete
dominance.
• A homozygous (BB) individual is blue, a homozygous
(bb) individual is red, and a heterozygous (Bb) individual
is purple.
• What would be the genotypes and phenotypes of the
offspring if a blue wildcat were crossed with a red one?
• Cross a Purple Cat and a Red cat. Can they have Blue
offspring?
Co-Dominance
• Longhorns may be white (CWCW), red (CRCR) or
roan (CRCW). Roan longhorns have a mixture of
both white hairs and red hairs due to a
codominant gene.
• Cross a Roan Bull with a Red Female!
• What are the genotypes and Phenotypes?
• Can roan cows produce more roan cows?