Complex Patterns of Inheritance

Mendel’s Laws Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only one copy of each gene in their gametes. Thus, the two copies of each gene segregate, or separate, during gamete formation.

Law of Independent Assortment: the alleles of different genes separate independently of one another during gamete formation

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

A) Hairy Ears: Gene on the Y Chromosome

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

A person with red-green color blindness sees a number 2

Hemophilia In this pedigree, only males are affected, and sons do not share the phenotypes of their fathers. –Thus, hemophilia is linked to a sex chromosome–the X. Expression of hemophilia often skips generations. –Thus, it is recessive. Extensive bruising of the left forearm and hand in a patient with hemophilia.

Genotypes for females X H X H = normal blood clotting, non-carrier X H X h = normal blood clotting, carrier of gene X h X h = female with hemophilia Queen Victoria of the United Kingdom was a carrier of hemophilia

Genotypes for Males X H Y = normal blood clotting X h Y = male with hemophilia Tsarevich Alexei of Russia had hemophilia

What is Alix’s genotype?

What is the probability that Anastasia was a carrier?

Cross a carrier mother with a normal father.

No daughters with hemophilia, ½ of sons with hemophilia X H X h X H X H X H X H X h Y X H Y X h Y

Cross a hemophiliac father with a normal (non-carrier) mother.

All daughers are carriers, no sons have hemophilia. X H X h X H X h Y X H Y

II. 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

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

What happens if you cross two pink snapdragons?

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

1 red (RR), 2 pink (RW), 1 white (WW)

Incomplete dominance in horse coat color

III. 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 

IV. Multiple Alleles Genes with three or more alleles for a particular trait. Examples are the ABO blood types, fur color in many animals.

Coat color in rabbits PhenotypeAllelePattern of Inheritance Dark gray coat C Dominant to all other alleles Chinchilla (silver-gray) c ch Dominant to Himalayan and white Himalayan (white with dark ears) c h Dominant to white White crecessive

1.List all possible genotypes for a: a) dark gray-coated rabbit CC, Cc ch, Cc h, Cc b) chinchilla rabbit c ch c ch, c ch c h, c ch c c) Himalayan rabbit c h c h, c h c d) white rabbit cc

2.Predict the phenotype for a rabbit with a c h c ch genotype chinchilla Predict the phenotype for a rabbit with a Cc h genotype dark gray 3.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

4.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”. 5.A chinchilla rabbit is mated with a Himalayan. Some offspring are white. What are the parents’ genotypes? Himalayan is c h c and chinchilla parent is c ch c

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

VI. Epistasis One gene that interferes with the expression of other genes. Example is with albinism. One gene interferes with all other genes for pigment production.

VII. 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