Biology 10 Notes on Complicated Patterns of Inheritance.

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More Complicated Patterns of Inheritance

Incomplete Dominance

Phenotype of heterozygous is different from homozygous parents

Intermediate btwn two parents

Neither allele is dominant


Pure red (RR) x Pure White (rr)

Bright Pink (Rr)

Red (R) is slightly dominate cuz carnations are bright pink not pale pink

Result of F2




Multiple Alleles

Gene that has many different allele forms

One person can only have 2 of these alleles (one of each chromosome of homologous pair)

But, there are many different alleles of that gene in the gene pool

Blood Types

4 Blood Types: A, B, AB, O

Determined by type of antigens found on surface of red blood cells

Type A = antigen A

Type B = antigen B

Type AB = antigen A & B

Type O = neither antigen

Blood phenotype controlled by gene "I"

3 different types of I: IA, IB, i

i = recessive

Genotypes A Antigen B Antigen Phenotype

IAIA + - A

IAi + - A

IBIB - + B

IBi - + B


ii - - O

Complicated Examples

Coat colour in rabbits is controlled by gene C

4 different alleles

Gene that controls production of glucose-6-phosphate dehydrogenase (enzyme)

80 alleles


When they have 2 or more dominant alleles

Both dominant alleles are expressed in phenotype

Blood Types


Gene Interaction

Single trait controlled by 2 or more genes acting 2gether

Coat Colour of Labrador Retrievers

2 Genes: B and E

B Gene: 2 alleles

B = Black coat (dominant)

b = Brown (recessive)

E Gene: 2 alleles

E = Golden coat (most dominant)

e = recessive to all genes

Phenotype Possible Genotypes

Golden Coat Eebb or EeBB or EeBb or Eebb or EEBB or EEBb

Black Coat eeBb or eeBB

Brown Coat eebb

Interaction can have many more genes & more complex

Like all cells and organs dependent on each other

Genes rarely act on their own

Genes that control flower colour depend on gene that controls flower production

Traits that show Continuous Range of Phenotypes

Instead of 2 or 3 distinct form


Results from many genes acting upon each other in different parts of body

Environment is also important

Cells can't reproduce w/o enuf nutrients