1. SPECIAL TYPES OF CROSSES

2. 1. Incomplete Dominance: When the phenotype of offspring result in a BLENDING of the trait.

3. The RED (RR) color of a four o’clock flower is incompletely dominant to the WHITE (rr) colored flower…hybrid offspring will be PINK (Rr).

4. Incomplete Dominance Example: four o’clock flowers
Mendelian Genetics
4/27/2017
Incomplete Dominance
Example: four o’clock flowers
red (RR) x white (WW)
RR = red flower
WW = white flower W RW RW R RW RW

5. Incomplete Dominance W R W All RW = pink (heterozygous pink)
Mendelian Genetics
4/27/2017
Incomplete Dominance W R W
All RW = pink
(heterozygous pink)
produces the
F1 generation RW

6. Mendelian Genetics
4/27/2017
2. Codominance
When BOTH alleles for a trait are represented in the heterozygous offspring.

7. The RED (RR) color of hair in horses is COdominant to white hair (WW)…hybrid offspring will have a ‘roan’ coat (RW) color… BOTH red and white hairs (“ROAN”)!

8. Red x White: RR x WW Roan x Roan: RW x RW R R R W W R W W

9. Genotype: RW Genotype: RR, RW, WW Genotypic Ratio: 4 RW : Genotypic Ratio: 1 RR : 2 RW : 1 WW Phenotype: Roan Phenotype: Red, Roan, White Phenotypic Ratio: 4 Roan : Phenotypic Ratio: 1 Red: 2 Roan: White

10. 3. Multiple Alleles – genes for which more than two different alleles exist.
Ex: skin color, eye color, hair color, blood type

11. Example: blood type A (dominant), B (dominant) AB (codominant), O (recessive) IA - blood type IB – blood type IAIB – blood type ii – blood type

12. GENOTYPES PHENOTYPES AA Type A AO Type A AB Type AB BB Type B
BO Type B
OO Type O

13. Codominance Problem IB IA i IAIB IBi IAi ii
Mendelian Genetics
4/27/2017
Codominance Problem
Example: A woman heterozygous for type B blood marries a man who is heterozygous type A. What are the possible genotypes and phenotypes of their children? heterozygous female Type B (IBi) x
heterozygous male Type A (IAi)
Geno – 1 IA IB :
1 IA i :
1 IB i :
1 ii
Pheno – 1 Type A : 1 Type B: 1 Type AB: 1 Type O IB IA i
IAIB
IBi
IAi ii

14. Another Codominance Problem
Mendelian Genetics
4/27/2017
Another Codominance Problem
Example: male Type O (ii) x female type AB (IAIB) i IA IB
IAi
IBi
1/2 = IAi
1/2 = IBi

15. Mendelian Genetics
4/27/2017
Codominance
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)

16. Codominance Answer: IB IA i IAIB ii Parents: genotypes = IAi and IBi
Mendelian Genetics
4/27/2017
Codominance
Answer: IB IA i
IAIB ii
Parents:
genotypes = IAi and IBi
phenotypes = A and B

17. 4. Sex-linked Traits Genes carried only on the sex chromosomes.
Mendelian Genetics
4/27/2017
4. Sex-linked Traits
Genes carried only on the sex chromosomes.
Ex: color blindness or hemophilia
XX genotype for females
XY genotype for males
1. Most sex-linked traits are
carried on X chromosome

18. 1. Most sex-linked traits are carried on X chromosome
2. The Y chromosome in males is
small and cannot carry/mask any
traits.
3. Therefore, males express sex-
linked traits more often than
females.
** Males that are affected don’t usually live past a certain age to pass on their traits to offspring.

19. Genotypes Phenotypes
XX Normal Female
XX* Carrier Female
X*X* Affected Female
XY Normal Male
X0Y Affected Male

20. Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes
Mendelian Genetics
4/27/2017
Sex-linked Traits
Example: Eye color in fruit flies
Sex Chromosomes
XX chromosome - female
Xy chromosome - male
fruit fly
eye color

21. Sex-linked Trait Problem
Mendelian Genetics
Sex-linked Trait Problem
4/27/2017
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 traits.
RR = red eyed
Rr = red eyed
rr = white eyed
XY = male
XX = female XR Xr Y

22. Sex-linked Trait Solution:
Mendelian Genetics
4/27/2017
Sex-linked Trait Solution: XR Xr Y
50% red eyed female
50% white eyed male
XR Xr
Xr Y

23. A woman who is a carrier for colorblindness marries a man who is colorblind. What are the possible genotypes and phenotypes of their children?
Genotypes:
Phenotypes:

24. Mendelian Genetics
4/27/2017
Female Carriers