dominance - loudoun county public schools...•incomplete dominance •codominance. incomplete...
TRANSCRIPT
Dominance
Relationships
Recap
• So …
• If you show the dominant phenotype, what could your genotype be?
•What is genotype and phenotype again?
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
a Aa
AA 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
Ff C
c
FC
FC FFCC(full lips, cleft chin)
Finish Up!
Fc fC fc
Numbers:
• How many Full Lips/Clefted Chins? _____
• How many Thin Lips/Clefted Chins? _____
• How many Full Lips/Non-clefted? _____
• How many Thin Lips/Non-clefted? _____
• So, what’s your HomD:Het:Het:HomR ratio?
___:___:___:___
9:3:3:1 -This is the classic ratio for a heterozygous dihybridcross!
9/16
3/16
3/16
1/16
9 3 3 1
Dominance Relationships
• Complete dominance: one allele shows full dominanceover 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
• Codominance
(Though darker colors tend to show more strongly than lighter colors)
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?