Transcript Let`s Review

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 Heterozygous Homozygous
RR
RW
WW
(Red)
(Pink)
(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 bluetipped feathers
 1. Incomplete Dominance or Codominance?
 2. Genotypes:
bluewhite –
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:
blacktan –
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:
curlyspiked –
wavy3. 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:
tallshort –
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:
whitepink –
red3. Show a cross between a white and red flower