Download 5.4 Co, Inc, Blood Typing

Co-dominance, Incomplete Dominance

Catalyst
 The
talkative allele is dominant to quiet.
 Create a Punnett square showing potential
offspring from a heterozygous father and
homozygous recessive mother.
 What percent of children will be homozygous
dominant? Homozygous recessive? Heterozygous?
Write in complete sentences!
Don’t talk during the Catalyst!
Objectives
By the end of today,
SWBAT…
Create and analyze Punnett
Squares for co-dominant and
incompletely dominant alleles.

Catalyst Review







Talkative = _____
Quiet = _____
Father = _____ _____
Mother = _____ _____
Homozygous dominant =
_____ %
Homozygous recessive =
_____ %
Heterozygous = _____ %
If You’re Confused About Percents…

A
a

A
AA
Aa


A
AA
Aa


Each square is one quarter of
the whole
What percent of the offspring
will be homozygous dominant?
What percent of the offspring
will be homozygous recessive?
What percent of the offspring
will be heterozygous?
What percent of the offspring
will show the dominant trait?
What percent of the offspring
will show the recessive trait?
50 cents
0=cents
50% =
50 0%
cents
100
cents
= 50%
= 100%
0 cents
= 0%
Review: Dominant/Recessive

A dominant allele is capable of masking,
or covering up, a recessive allele.
PP = purple
pp = white
Pp = purple
Review: Dominant/Recessive

In pea plants, purple flowers (P) are dominant over white
flowers (p). Show the potential offspring between two
heterozygous plants.
P
GENOTYPES:



PP: 25%
Pp: 50%
pp: 25%
PHENOTYPES:


Purple: 75%
White: 25%
p
P
PP
Pp
p
Pp
pp
Incomplete Dominance

Key Point #1:
In
incomplete dominance, one allele does
not mask the other. In heterozygotes, the
dominant and recessive alleles BLEND
TOGETHER.

Example: In snapdragon flowers, red (R)
and white (r) are incompletely dominant.
Incomplete Dominance
Guided Practice (GP) 1



In humans, being tall (T) and short (t) is incompletely
dominant.
Show the potential offspring of a heterozygous father and
a homozygous recessive mother.
Fill in percents for genotype and phenotypes.
GENOTYPES:



TT:
Tt:
tt:
PHENOTYPES:



Tall:
Short:
Medium:
Guided Practice (GP) 2



In African-Americans, dark skin (D) and light skin (d) are
incompletely dominant.
Show the potential offspring of a homozygous dominant
father and a homozygous recessive mother.
Fill in percents for genotype and phenotype.
GENOTYPES:
PHENOTYPES:
Guided Practice (GP) 3



In dragons, long tails (L) and short tails (l) are incompletely
dominant.
Show the potential offspring of a homozygous recessive
father and a heterozygous mother.
Fill in percents for genotype and phenotype.
GENOTYPES:
PHENOTYPES:
Co-Dominance

Key Point #2:
 In
co-dominance, both alleles are dominant. In
heterozygotes, both alleles are expressed EQUALLY.

Example: Sick cell anemia in humans
AA =
normal cells
SS = sickle cells
AS = half of
each
Sickle Cell Anemia
Sickle cells easily get stuck in the
circulatory system.
Why would African
Americans be so much
more likely to have
Sickle Cell anemia?
The story gets more interesting



People who are AA get malaria and (may)
die.
People who are SS (may) die from sickle cell
anemia.
People who are AS are resistant to malaria!!!
 Having
some sickled cells hurts them, but the
benefit outweighs the cost
Sickle Cell Anemia



Being normal (A) and having sickle cell anemia (S) are co-dominant.
Show the potential offspring of a normal father and a heterozygous
mother.
Fill in percents for genotype and phenotype.
A
A
A
AA
AA
S
AS
AS
GENOTYPES:



AA: 50%
AS: 50%
SS: 0%
PHENOTYPES:



Normal: 50%
Some normal, some sickle: 50%
Sickle Cell: 0%
GP 4



Being normal (A) and having sickle cell anemia (S) are codominant.
Show the potential offspring of two heterozygous people.
Fill in percents for genotype and phenotype.
GENOTYPES:



AA:
AS:
SS:
PHENOTYPES:



Normal:
Some normal, some sickle:
Sickle Cell:
GP 5


In cows, color is co-dominant. Show the potential offspring
between a white bull (WW) and a red cow (RR).
Fill in percents for genotype and phenotype.
GENOTYPES:
PHENOTYPES:
GP 6


In dragons, teeth can either be long (L) or sharp (S). Show the
potential offspring between a heterozygous dragon, and a
dragon that is homozygous for sharp teeth.
Fill in percents for genotype and phenotype.
GENOTYPES:
PHENOTYPES:
Conclusion

Incomplete dominance:
Heterozygotes
are a BLEND of the two
alleles.
Example: pink snapdragon flowers

Co-dominance:
Heterozygotes
show BOTH alleles
EQUALLY.
Example: sickle cell trait, roan cows
Exit Question


In Mr. J’s students, raising your hand to participate
(R) and shouting out questions (r) is INCOMPLETELY
DOMINANT. Dweldon and Dajha want to have
children. Dweldon is heterozygous, and Dajha is
homozygous dominant.
Create a Punnett square showing potential
offspring.
 List
the percent probability of each genotype AND
phenotype