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.

List the percentages for genotype AND phenotype

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…

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?

A a

A

A

AA Aa

AaAA

50 cents = 50%0 cents =

0%50 cents = 50%100 cents

= 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

In pea plants, purple flowers (P) are dominant over white flowers (p). Show the potential offspring between two heterozygous plants.

P

p

P p

pp

Pp

Pp

PPGENOTYPES:

PHENOTYPES:

PP: 25% Pp: 50% pp: 25%

Purple: 75% White: 25%

Review: Dominant/Recessive

Incomplete Dominance

Key Point #1: In incomplete dominance, one allele does not mask the other. In heterozygotes, the phenotype is IN BETWEEN dominant and recessive.

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:

PHENOTYPES:

TT: Tt: tt:

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 humansAA = 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

die.

People who are SS have decreased life expectancy.

People who are AS are resistant to malaria!!! Having some sickled cells hurts them,

but the benefit outweighs the cost

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.

GENOTYPES:

PHENOTYPES:

AA: 50% AS: 50% SS: 0%

Normal: 50% Some normal, some

sickle: 50% Sickle Cell: 0%

Sickle Cell Anemia

A

S

A A

AA

AS

AA

AS

GENOTYPES:

PHENOTYPES:

AA: AS: SS:

Normal: Some normal, some

sickle: Sickle Cell:

GP 4 Being normal (A) and having sickle cell anemia (S) are

co-dominant. Show the potential offspring of two heterozygous people. Fill in percents for genotype and phenotype.

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 5

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:

GP 6

Conclusion

Incomplete dominance: Heterozygotes are a BLEND of the two alleles.

Example: pink snapdragon flowersCo-dominance:

Heterozygotes show BOTH alleles EQUALLY.

Example: sickle cell trait, roan cows

Exit Question

In Mr. LY’s students, raising your hand (R) and shouting out answers (r) is INCOMPLETELY DOMINANT. Angelina is heterozygous, and Jaron is homozygous recessive.

Create a Punnett square showing potential offspring. List the percent probability of each

genotype AND phenotype Write in complete sentences!

Don’t talk during the Exit Question!