Beyond Dominant & Recessive Alleles Heredity Beyond Dominant & Recessive Alleles Incomplete Dominance & Codominance

Learning Goals 1. Describe incomplete dominance. Describe codominance. 2. Compare and contrast incomplete dominance and codominance. Give 2 similarities and 1 difference. 3. Explain how letters are chosen when doing Punnett square problems for incomplete dominant and codominant traits

Beyond Dominant and Recessive Alleles Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. This power point will address traits that are neither dominant nor recessive. The rest you will learn later in high school.

Incomplete Dominance  Incomplete dominance - when one allele is not completely dominant over another. Heterozygous genotype = BLEND Since one allele is not completely dominant over the other allele, we use two different capital letters to represent the alleles

Example: Snapdragons Example: A cross between red (RR) and white (WW) snapdragons produces pink flowers (RW). The colors blend to make pink.

How incomplete dominant genotypes are written As you probably noticed, incomplete dominant genotypes use only capital letters. Remember: Heterozygous (hybrid) traits that express incomplete dominance are represented by two different capital letters.

Homozygous RR (Red) Heterozygous RW (Pink) Homozygous WW (White)

Another Example of Incomplete Dominance Baaaaaaaa!

Codominance  Codominance - both alleles contribute to the phenotype. No blending. Heterozygous genotype = both traits appear Since one allele is not completely dominant over the other allele, and both traits appear together, we use two different capital letters to represent the alleles

Codominance in Chickens Example: A cross between black (BB) and white (WW) chickens produces chickens speckled with black and white feathers (BW).

Roan Cows Codominance- unlike red and white snapdragons, both the red and white are expressed in cows. They are not blended to make a “pink” cow.

Roan Horse Draw a punnett square to show how this roan horse got its trait.

Other Codominant Phenotypes

More Codominance Examples Bird wings Flowers

Just kidding! You get the idea…..

Codominance in Humans Sickle Cell Anemia The altered form of hemoglobin that causes sickle-cell anemia is inherited as a codominant trait.

Learning Goals 1. Describe incomplete dominance. Describe Codominance. 2. Compare and contrast incomplete dominance and codominance. Give 2 similarities and 1 differences 3. Explain how letters are chosen when doing punnett square problems for incomplete dominant and codominant traits

Whiteboard Practice Step 1: Is the example showing Incomplete Dominance or Codominance?????? Step 2: You will be given the 3 phenotypes, Write the corresponding genotypes. 2 alleles (1 from mom, 1 from dad) Use the 1st letter for each trait Both letters are capitol Step 3: Set up and fill-in a punnett square. Calculate percent probability for ALL 3 TRAITS!!!

Let’s do the 1st one together  Birds can be blue, white, or white with blue-tipped feathers 1. Incomplete Dominance or Codominance? 2. Genotypes: blue- white – blue-tipped – 3. Show a cross between a white and blue-tipped bird

Practice Identifying A cat can be black, tan, or tabby (black & tan) 1. Incomplete Dominance or Codominance? 2. Genotypes: black- tan – tabby – 3. Show a cross between a heterozygous tabby and tan cat

Practice Identifying A Who can have curly hair, spiked hair, or wavy 1. Incomplete Dominance or Codominance? 2. Genotypes: curly- spiked – wavy- 3. Show a cross between a curly and wavy Who

Practice Identifying A sneech can be tall, short, or medium 1. Incomplete Dominance or Codominance? 2. Genotypes: tall- short – medium – 3. Show a cross between two heterozygous sneeches

Practice Identifying A horse can be black, white, or roan (black & white) 1. Incomplete Dominance or Codominance? 2. Genotypes: black – white – roan - 3. Show a cross between a heterozygous roan and black horse

Practice Identifying Flowers can be white, pink, or red 1. Incomplete Dominance or Codominance? 2. Genotypes: white- pink – red- 3. Show a cross between a white and red flower