Incomplete Dominance Codominance Multiple 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 = purple pp = white

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 GENOTYPES: - PP (1); Pp (2); pp (1) - ratio 1:2:1 P p PP Pp PHENOTYPES: Pp pp - purple (3); white (1) - ratio 3:1

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. GENOTYPES: R r - RR (1); Rr (2); rr (1) - ratio 1:2:1 R r Rr rr RR PHENOTYPES: Red (1); Pink (2); white (1) - ratio 1:2:1

Problem: Incomplete Dominance Show the cross between a pink and a white flower. GENOTYPES: R r - Rr (2); rr (2) - ratio 1:1 r rr Rr PHENOTYPES: - pink (2); white (2) - ratio 1:1

Codominance The heterozygous condition, both alleles are expressed equally Sickle Cell Anemia in Humans SS = sickle cells NN = normal cells NS = some of each sick

What do you notice about the letters N and S in the Genotypes of F1? Sickle cell anemia http://www.netwellness.org/ency/imagepages/1223.htm Problem: Codominance Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick. N S GENOTYPES: - NS (2) SS (2) - ratio 1:1 S NS SS PHENOTYPES: - carrier (2); sick (2) - ratio 1:1 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 RW Look at the Phenotype of the HETEROZYGOUS offspring

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. Io Io GENOTYPES: IA Io (2) IB Io (2) - ratio 1:1 IA IB IA Io IB Io PHENOTYPES: - type A (2); type B (2) - ratio 1:1 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!)