1. Complex Patterns of Inheritance

2. I. Incomplete Dominance
An individual displays a trait that is intermediate between the two parents
Example: a red snapdragon
crossed with a white
snapdragon produces
pink offspring

3. Red = RR, White = WW, Pink = RW

4. Make a Punnett square for a red plant crossed with a white plant
R R W

5. All offspring are pink, with RW genotype
R R RW W

6. Show the cross between two pink snapdragons

7. Offspring are 1 red, 2 pink, and 1 white
R W RR RW WW R W

9. Incomplete
dominance
in horse
coat color

10. II. Codominance Two dominant alleles are expressed at the same time
Roan coat color in horses or cows is an example
A roan horse has both red and white hairs

11. Roan 
has red
and white
hairs

12. Parents  
Codominance
in chicken
feather color.
Black and
White feathers 

13. III. Multiple Alleles Traits controlled by more than 2 alleles.
Examples are pigeon feather colors
and fur color in many animals.

14. Pattern of Inheritance
Coat color in rabbits
Phenotype
Allele
Pattern of Inheritance
Dark gray coat C
Dominant to all other alleles
Chinchilla (silver-gray)
cch
Dominant to Himalayan and white
Himalayan
(white with dark ears) ch
Dominant to white
White c
recessive

15. List all possible genotypes for a:
a) dark gray-coated rabbit
CC, Ccch, Cch, Cc
b) chinchilla rabbit
cchcch, cchch, cchc
c) Himalayan rabbit
chch, chc
d) white rabbit cc

16. Predict the phenotype for a rabbit with a chcch genotype
chinchilla
Predict the phenotype for a rabbit with a Cch genotype
dark gray
Would it be possible to obtain white rabbits if one parent is white and the other is chinchilla?
Yes, if the chinchilla parent has a white allele

17. Would it be possible to obtain chinchilla rabbits if one parent is Himalayan and the other is white?
No, because chinchilla is dominant to both Himalayan and white, so the allele couldn’t be “hiding”.
A chinchilla rabbit is mated with a Himalayan. Some offspring are white. What are the parents’ genotypes?
Chinchilla is cchc and Himalayan is chc .

18. IV. Sex-linked traits
A sex-linked trait is a trait whose allele is located on either the X or Y chromosome.

19. A) Hairy Ears are caused by a gene on the Y Chromosome
Hairy Ears: Gene on the Y Chromosome
Here, we denote “H” for the hairy ear gene on the Y chromosome.
Reference
Campbell, N. E. & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.
Image Reference
Young, M. (2005). Pedigree chart. Houston, TX: Baylor College of Medicine, Center For Educational Outreach.

20. B) Most sex-linked traits on X chromosome are recessive
Examples include: hemophilia, red-green colorblindness, and a form of muscular dystrophy

21. People with red-green color blindness see the number 35, while people with normal vision see the number 57

23. Hemophilia A disorder in which the blood does not clot properly
Sex-linked recessive (on the X chromosome)
Males receive the hemophilia gene from their mothers
Extensive bruising of the left forearm and hand in a patient with hemophilia.
Hemophilia
Hemophilia is a condition of excessive bleeding caused by missing clotting factors in the blood. Hemophiliacs are prone to bruising, as illustrated in the photo here, and to other, potentially fatal, risk factors. In this pedigree, there is a trend for only males to express the trait strongly suggesting the role of sex chromosomes. However, the sons do not share the phenotypes of their fathers, so the Y chromosome is not a likely candidate. Thus, we can conclude that the gene for hemophilia is on the X chromosome.
Since the trait skips generations, we can assume that an allele for hemophilia is recessive to an allele for normal blood clotting factors. Although rare, a female can be afflicted if she inherits an allele for hemophilia on both X chromosomes.
Reference
Campbell, N. E. & Reece, J. B. (2002). Biology (6th ed.). San Francisco: Benjamin Cummings.
Image Reference
Young, M. (2005). Pedigree chart. Houston, TX: Baylor College of Medicine, Center For Educational Outreach.
Hemophilia A. Retrieved from

24. Genotypes for females XHXH = normal blood clotting, non-carrier
XHXh = normal blood clotting, carrier of gene
XhXh = female with hemophilia
Queen Victoria of the
United Kingdom was a
carrier of hemophilia

26. Genotypes for Males XHY = normal blood clotting
XhY = male with hemophilia
Tsarevich Alexei of Russia
had hemophilia

27. What is Alix’s genotype?

28. What is the probability that Anastasia was a carrier?

29. 1. Cross a carrier mother with a normal father.XH Xh Y

30. What percent of sons have hemophilia
What percent of sons have hemophilia? What percent of daughters have hemophilia? XH Xh
XHXH
XHXh Y
XHY
XhY

31. 50% of sons have hemophilia, 0% of daughters have hemophilia.XH Xh
XHXH
XHXh Y
XHY
XhY

32. 2. Cross a hemophiliac father with a normal (non-carrier) mother.XH Xh Y

33. What percent of sons have hemophilia
What percent of sons have hemophilia? What percent of daughters are carriers? XH Xh
XHXh Y
XHY

34. 0% percent of sons have hemophilia
0% percent of sons have hemophilia % percent of daughters are carriers. XH Xh
XHXh Y
XHY

35. 3. Cross a carrier mother with a hemophiliac father.XH Xh Y

36. What percent of sons have hemophilia
What percent of sons have hemophilia? What percent of daughters have hemophilia? XH Xh
XHXh
XhXh Y
XHY
XhY

37. 50% percent of sons have hemophilia
50% percent of sons have hemophilia. 50% percent of daughters have hemophilia. XH Xh
XHXh
XhXh Y
XHY
XhY

38. Cross a hemophiliac mother with a normal father
What percent of sons have hemophilia?
What percent of daughters have hemophilia?

39. 100% percent of sons have hemophilia
100% percent of sons have hemophilia. 0% percent of daughters have hemophilia. Xh XH
XHXh Y
XhY

42. V. Polygenic traits Traits that are influenced by 2 or more genes
Examples include human height, weight, hair color, eye color, and skin color

45. Coat color in Labrador retrievers

46. Coat color in Labrador retrievers

47. Is it possible for two chocolate lab parents to have black lab offspring?

48. VI. Traits influenced by the environment.
Color of hydrangea flowers (blue in acidic soil, pink in basic soil)

49. Color of arctic fox
Human height, skin color, behavior