Co-dominance Co-dominance when both alleles of a gene
contribute to the phenotype Examples: Chickens black feathers is
co- dominant with white feathers, so heterozygous chickens show up
with speckled black and white feathers Human Blood Types
Slide 3
Human Blood Types are another example of co- dominance There
are 3 alleles for this gene (I A, I B & i) and i is recessive,
while I A and I B are co-dominant, so people who receive one of
each of these alleles will have AB blood IAIAIAiIAIAIAi
IBIBIBiIBIBIBi IAIBIAIB
Slide 4
Co-Dominance Sample Problems #1 Use the chart to answer the
following questions: Write the genotype for each person based on
the description: Homozygous for the B allele I B I B Heterozygous
for the A allele I A i Type O ii Type AB I A I B
Slide 5
Co-Dominance Sample Problem #2 Pretend that Brad Pitt is
homozygous for the type B allele, and Angelina Jolie is type O. Do
a Punnett square to determine all the possible blood types of their
baby. All their offspring, will be I B i, so will have Type B blood
i ii i I B I B IBiIBi IBiIBi IBiIBiIBiIBi
Slide 6
Co-Dominance Sample Problem #3 Two parents think their baby was
switched at the hospital. The mother has blood type A, the father
has blood type B, and the baby has blood type AB. Mothers genotype
I A I A or I A i Fathers genotype I B I B or I B i Babys genotype I
A I B Do a Punnett square that shows the babys genotype as a
possibility Was the baby switched? NO IB iIB i I A i IAIBIAIB
IBiIBi iiIAiIAi
Slide 7
Co-Dominance Sample Problem #4 Based on the information in this
table, which man could not be the father of the baby? Justify your
answer with a Punnett square. Sammy the player NameBlood Type
MotherType A (Heterozygous) BabyType B Sammy the playerType O
George the sleezeType AB The waiterType AB The cable guyType B i ii
i I A i IAiIAi ii IAiIAi
Slide 8
Probability What is probability? The likelihood a particular
event will occur How is it used in Biology? Used to predict
phenotypes and genotypes of offspring (diseases & disorders for
people planning families)
Slide 9
Additional Information Probability = # of times an event occurs
# of trials A previous event does not affect future outcomes. Each
event is separate and independent Ex. Gender of baby 50/50 chance
of each sex each birth
Slide 10
Incomplete Dominance Incomplete Dominance when one allele is
not completely dominant over the other allele, so it produces
offspring with a third phenotype that is a blending of the parental
traits. It's like mixing paints, red + white will make pink. Red
doesn't totally block (dominate) the white, instead there is
incomplete dominance, and we end up with something in-between.
Instead of using a capital letter for the dominant trait & a
lowercase letter for the recessive trait, the letters we use are
both going to be capital (because neither trait dominates the
other).
Slide 11
Incomplete Dominance Four oclock flowers show this type of
inheritance Red flowers are RR, white are WW and the heterozygous
genotype RW, gets you pink flowers So looking at the following
Punnett Square, what percentage of pink flowers would be produced?
100%
Slide 12
Incomplete Dominance Sample Problem #1 Suppose you cross 2 pink
flowers that show incomplete dominance (R=Red, W=W). What are the
parent genotypes? RW; RW Do a Punnett Square. What is the
probability of: Red 25% White 25% Pink 50% R WR W R W RR RW WW
Slide 13
Incomplete Dominance Sample Problem #2 In Elmos family red (R)
and blue (B) show incomplete dominance. What is the Genotype of:
Red RR Blue BB Purple RB
Slide 14
Incomplete Dominance Sample Problem #3 If both of Elmos parents
were purple, what is the probability that his next sibling will be
blue (Do a Punnett square to show your results)? 25% R BR B R B RR
RB BB