1. Genetics : Special Cases

2. One allele cannot completely dominate the other.
Incomplete Dominance
One allele cannot completely dominate the other.
A new trait is produced

3. Incomplete Dominance

4. Incomplete Dominance Example: snapdragons (flower)
red (R) x white flower (r)
RR = red flower
rr = white flower
Rr = pink flower R r

5. Incomplete Dominance R r Rr Genotypes: Rr Genotypic Ratio: all alike
Phenotypes: Pink
Phenotypic Ratio: all alike r R Rr

6. Incomplete Dominance Example: snapdragons (flower)
red (R) x white flower (r)
RR = red flower
rr = white flower
Rr = pink flower R r R r

7. Incomplete Dominance Genotypes: RR,Rr,rr Genotypic Ratio: 1 : 2 : 1
Phenotypes:
Red : Pink : White
Phenotypic Ratio: R r RR Rr Rr rr

8. Cross a red (RR) flower with a pink flower (RW)
Incomplete Dominance
In snapdragons, red (RR) flowers and white flowers (WW) are incompletely dominant and when crossed produce a new phenotype: pink flowers (RW).
Cross a red (RR) flower with a pink flower (RW)
What is the probability of having white offspring?
What is the probability of having Pink offspring?
What is the probability of having Red offspring?
What is the probability of having Heterozygous offspring?
What is the probability of having Homozygous offspring?

9. Codominance
When both dominant alleles show in the offspring

10. Sex – Linked Traits Traits (genes) located on the sex chromosomes
XX genotype for females
XY genotype for males
Sex – linked traits are usually carried on the X chromosome

11. Sex – Linked Traits Example: Eye color in fruit flies Sex Chromosomes
XX chromosome - female
Xy chromosome - male
fruit fly
eye color

12. Sex – Linked Trait Problem
Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female) XRY x XrXr
Remember: the Y chromosome in males does not carry this trait.
RR = red eyed
Rr = red eyed
rr = white eyed
Xy = male
XX = female Xr XR y

13. Sex – Linked Trait Xr XR y 50% red eyed female 50% white eyed male

14. Multiple Allele Traits
Traits having more than one allele that can be found in a population
Example: Human Blood Types has 3 alleles rather than 2
There are four
distinctly different
Blood types

15. Multiple Allele Problem
Example:
homozygous female Type B (IBIB)
x heterozygous male Type A (IAi) IB IB
Genotypes= IAIB, IBi
Genotypic Ratio=2:2
Phenotypes=AB,B
Phenotypic Ratio=2:2
IAIB
IAIB IA
IBi
IBi i

16. Multiple Allele Problem
Example: male Type O (ii) x female type AB (IAIB) i IA IB
IAi
IBi
1/2 = IAi
1/2 = IBi

17. Multiple Allele
Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents?
boy - type O (ii) X girl - type AB (IAIB)

18. Multiple Allelle Answer: IB IA i IAIB ii Parents:
genotypes = IAi and IBi
phenotypes = A and B

19. Female Carriers

20. Green = AaBbCc Light Blue = aabbcc Polygenic Traits
Traits that are controlled by several genes at
the same time
Example: Human Eye Color
Alleles : A, a, B, b, C, c
Dark Brown = AABBCC
Green = AaBbCc
Light Blue = aabbcc