1. Incomplete Dominance and Co-Dominance
BIOLOGY 12
Incomplete Dominance and Co-Dominance

2. Incomplete Dominance
a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele
results in a combined phenotype (ie. blend)

3. Incomplete Dominance
two alleles are equally dominant, producing a new phenotype
the genotypes are written as normal; heterozygous indicates a blend

4. Incomplete Dominance
example: in cross-pollination experiments between red and white snapdragon plants, the resulting offspring are pink
the dominant allele that produces the red color is not completely expressed over the recessive allele that produces the white color

6. Incomplete Dominance Practice
in snapdragons, a pink-flowered plant is crossed with a red-flowered plant
write the genotypes of each parent
create a punnett square for the cross
what is the probability of producing a pink-flowered plant?

7. Co-Dominance
the contribution of both alleles are visible in the phenotype
equally and fully
both alleles are shown in the offspring (ie. spotted)

8. Co-Dominance example: cattle can be:
red (all red hairs)
white (all white hairs),
or roan (red & white hairs together)
the colours are both shown in the offspring
the genotype is now written with superscripts

9. Co-Dominance Practice
in some chickens, the gene for feather color is controlled by co-dominance. the allele for black is B and the allele for white is W. the heterozygous phenotype is known as erminette
what is the genotype for black chickens?
what is the genotype for white chickens?
if two erminette chickens were crossed, what are the possible phenotypes?

10. Practice Together
in certain species of fish, blue scales are incompletely dominant over yellow scales. heterozygous fish show a green phenotype. predict the outcome between two heterozygous fish.
BB = blue
bb = yellow
Bb = green

11. Predict the outcome between two heterozygous fish.
B b BB Bb B b Bb bb

12. Predict the outcome between two heterozygous fish.
Genotype: 25% BB
25% bb
50% Bb
Phenotype: 25% Blue
25% Yellow
50% Green

13. Practice Together
in some species of frogs, green skin and purple skin are co-dominant.
predict the outcomes between two heterozygous frogs.

14. Predict the outcomes between two heterozygous frogs.

15. Predict the outcomes between two heterozygous frogs.
phenotype 25% green
25% purple
50% spotted