beyond dominant and recessive alleles...
TRANSCRIPT
Beyond Dominant & Recessive Alleles
Incomplete Dominance & Codominance
Beyond Dominant and Recessive Alleles
•Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.
Incomplete Dominance
SIncomplete dominance -‐ when one allele is not completely dominant over another.SHeterozygous genotype = BLEND
SSince one allele is not completely dominant over the other allele, we use two different capital letters to represent the alleles
Incomplete Dominance
•Example: A cross between red (RR) and white (WW) snapdragons produces pink flowers (RW).
Homozygous
RR
(Red)
Heterozygous
RW
(Pink)
Homozygous
WW
(White)
Codominance
SCodominance -‐ both alleles contribute to the phenotype.SHeterozygous genotype = both traits appear
SSince 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
•Example: A cross between black (BB) and white (WW) chickens produces chickens speckled with black and white feathers (BW).
Multiple Alleles
•Multiple alleles -‐genes that are controlled by more than two alleles.•An individual can’t have more than two alleles (Remember you get one copy from each parent). •However, more than two possible alleles can exist in a population.
•Example: A human’s blood type is determined by a single gene that has three different alleles.
Polygenic Traits
•Polygenic traits -‐traits controlled by two or more genes.• Skin color in humans is a polygenic trait controlled by more than four different genes.
Whiteboard Practice
• Step 1: 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 J
SBirds can be blue, white, or white with blue-‐tipped feathers
S1. Incomplete Dominance or Codominance?S2. Genotypes:blue-‐white –blue-‐tipped –
3. Show a cross between a white and blue-‐tipped bird
Practice Identifying
SA cat can be black, tan, or tabby (black & tan)
S1. Incomplete Dominance or Codominance?S2. Genotypes:black-‐tan –tabby –
3. Show a cross between a heterozygous tabby and tan cat
Practice Identifying
SA Who can have curly hair, spiked hair, or wavy
S1. Incomplete Dominance or Codominance?S2. Genotypes:curly-‐spiked –wavy-‐
3. Show a cross between a curly and wavy Who
Practice Identifying
SA sneech can be tall, short, or mediumS1. Incomplete Dominance or Codominance?S2. Genotypes:tall-‐short –medium –
3. Show a cross between two heterozygous sneeches
Practice Identifying
SA horse can be black, white, or roan (black & white)
S1. Incomplete Dominance or Codominance?S2. Genotypes:black –white –roan -‐
3. Show a cross between a heterozygous roan and black horse
Practice Identifying
SFlowers can be white, pink, or redS1. Incomplete Dominance or Codominance?S2. Genotypes:white-‐pink –red-‐
3. Show a cross between a white and red flower