Bell Work

• In dogs, erect ears is dominate over droopy ears. What are the results if two heterozygous dogs have a litter of puppies.

• Genotype:• Phenotype:

Biology – Lecture 49

Punnett Squares with Co and Incomplete Dominance

Genetics Vocabulary

• Incomplete dominance - expressing an intermediate phenotype

• Co-dominance - expressing both alleles at once

In Both Situations

• Neither trait is dominant over the other one.• A middle or hybrid trait is achieved.• Each trait can get its own letter or one trait

can be capital regular and the other can be capital prime.

• Neither letter can be lowercase because neither trait is recessive.

Incomplete Dominance

• This is when the heterozygous genotype is “in between” the two homozygeous genotypes.

• Neither phenotype is actually shown.

Example of Incomplete Dominance

• Height– Short (SS), Medium (TS), Tall (TT)

• Hair Color– Black Hair (BB), Brown Hair (BB’), Blonde Hair

(B’B’)

Co-dominance

• An organism that has both alleles of a gene and displays both phenotypes at the same time.

• It is not an “in-between” trait, but rather that both traits are shown.

Examples of Co-Dominance

• The fur of animals– Black Fur (BB), Speckled Fur (BT), Tan Fur (TT)

Example Problems

• In humans, wavy hair (CS) results by the co-dominant situation of curly hair (C) and straight hair (S). What are the possible results if a curly-haired man and wavy-haired woman have children.

• In iris, purple (P) is incompletely dominant over white (W). What would be the results of a cross if both parents were pale lavender?

• In crocus flowers, white (W) and purple (P) colors are co-dominant, and result in a purple and white striped flower when both genes are present. What are the possible results from the cross-pollination of a striped crocus with a white crocus?

• In cattle, red (R) is incompletely dominant over white (W) hides. Roan in the name of the color that results from incomplete dominance. What are the possible results if a white male mates with a roan female?

• Black hair is homozygous dominant. Brown hair is heterozygous. Blonde hair is homozygous recessive. (This is an example of incomplete dominance.) A woman with brown hair marries a man with brown hair. What are genotypes and phenotype possibilities for their kids?

• Height is an example of incomplete dominance. The alleles are as follows: T=tall (5’11”-6’2”); TS=medium height (5’4”-5’10”) S=short (5’3” or smaller).

• If Mom is 5’5”, and Dad is 6’0”, what are the possible height outcomes of their children?

• A cross between red-flowered snapdragons and white-flowered snapdragons produces offspring with pink flowers. Is this co-or incomplete dominance? Show the punnett square and the genotype/phenotype.

• Using the previous example, suppose a pink-flowered plant is crossed with a pink-flowered plant. What is the genotype and phenotype of the offspring?

• There are three possible genotypes and phenotypes for wing color in a species of moth: RR = red wings; RY = orange wings; YY = yellow wings.

• What are the genotypes and phenotypes of a cross between an orange winged moth and a yellow winged moth?

• A tabby cat (co-dominant black/tan) is crossed with a tan cat. What are the possible outcomes of their children?

• In a fictional species of mice, one gene determines fur color. Let B = black fur and W = white fur. If this is co-dominance, what will the offspring look like? If this is incomplete dominance, what will the offspring look like?