Incomplete DominanceCodominanceMultiple Alleles

In a nutshell!

HW: Complete the HW

Packet (by Monday)

Resubmission of genetics Quiz 2 by Monday

Review: Dominant/Recessive

• One allele is dominant over the other (capable of masking the recessive allele)

PP = purple pp = white Pp = purple

Review Problem: Dominant/Recessive

• In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants.

P

p

P p

pp

Pp

Pp

PP- PP (1); Pp (2); pp (1)- ratio 1:2:1

- purple (3); white (1)- ratio 3:1

GENOTYPES:

PHENOTYPES:

Incomplete Dominance

• A third (new) phenotype appears in the heterozygous condition.

RR = red rr = white Rr = pink

Problem: Incomplete Dominance

• Show the cross between a red and a white flower.

- RR (1); Rr (2); rr (1)- ratio 1:2:1

-Red (1); Pink (2); white (1)- ratio 1:2:1

R r

R

r

Rr

rrRr

GENOTYPES:

PHENOTYPES:

RR

Problem: Incomplete Dominance

• Show the cross between a pink and a white flower.

- Rr (2); rr (2)- ratio 1:1

- pink (2); white (2)- ratio 1:1

R r

r

r

rrRr

rrRr

GENOTYPES:

PHENOTYPES:

Codominance• The heterozygous condition,

both alleles are expressed equally

NN = normal cells

SS = sickle cells NS = some of each

Sickle Cell Anemia in Humans

Problem: Codominance• Show the cross between an individual with

sickle-cell anemia and another who is a carrier but not sick.

N S

S

S

NS

NS

SS

SS

- NS (2) SS (2)- ratio 1:1

- carrier (2); sick (2)- ratio 1:1

GENOTYPES:

PHENOTYPES:

What do you notice about the letters N and S in the Genotypes of F1?

How Do We Determine If a Trait IS

• Dominant/Recessive• Incomplete

Dominance• Co-Dominance

• Rr • Rr

• RW

Multiple Alleles

• Sometimes there are more than two alleles for a trait – can you think of any?

• Blood type in humans

• Blood Types?– Type A, Type B, Type AB, Type O

• Blood Alleles?– A, B, O (often expressed – IA, IB, I)

Rules for Blood Type

• A and B are codominant– AA = Type A– BB = Type B– AB = Type AB

• A and B are dominant over o– Ao = type A– Bo = type B– oo = type O

Problem: Multiple Alleles• Show the cross between a mother who has type O

blood and a father who has type AB blood.

-IA Io (2) IB Io (2)- ratio 1:1

- type A (2); type B (2)- ratio 1:1

GENOTYPES:

PHENOTYPES:

Io Io

IA

IB

IA Io

IB Io

IA Io

IB Io

What do you notice about the letters N and S in the Genotypes of F1?

Blood Type – Two Ways to Write It

In Cases of CO-Dominance

• Both alleles are expressed in the heterozygote and both take a CAPITAL CASE letter

• An index letter may identify the allele

Therefore (Blood):

• Normal haemoglobin allele is also HbN

• Sickle cell allele is also HbS

Comprehension Questions

• ROAN CATTLE• Red Hair (RR)• White (WW)• HETEROZYGOUS = • Is this

– A: Codominance– B: Incomplete Dominance

What color is the Heterozygous Offspring?

BIRD WINGS

• White Wings (WW)

• Blue Wings (BB)

• Heterozygous =

• What gives it away that it is CO-Dominance?

Rose Color

• Red Rose (RR)• White Rose (ww)• Heterozygous =• Is this

– A: Codominance– B: Incomplete Dominance

• What gives it away that it is Incomplete-Dominance?

Human Skin Color

• Incomplete dominance

• Controlled by 4 to 6 genes!!!

• (Take Away – ONE CHARACTERISTIC MAY BE CONTROLLED BY MULTIPLE GENES!)