Complex Patterns of Inheritance

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

Red = RR, White = WW, Pink = RW

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

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

Show the cross between two pink snapdragons

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

Incomplete dominance in horse coat color

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

Roan  has red and white hairs

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

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

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

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

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

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 .

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

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.

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

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

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 08-10-2006 from http://medgen.genetics.utah.edu/index.html

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

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

What is Alix’s genotype?

What is the probability that Anastasia was a carrier?

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

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

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

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

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

0% percent of sons have hemophilia 0% percent of sons have hemophilia. 100% percent of daughters are carriers. XH Xh XHXh Y XHY

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

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

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

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

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

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

Coat color in Labrador retrievers

Coat color in Labrador retrievers

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

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

Color of arctic fox Human height, skin color, behavior