11.3 Other Patterns of Inheritance

Beyond dominant and recessive

*Not everything follows Mendel’s rules

• There are exceptions to Mendel’s principles• Genetics is complicated because the majority

of genes have more than two alleles• Traits can be controlled by more than one

gene• Genetics goes WAY beyond pure dominance

and recessiveness…

I. Incomplete dominance• Incomplete dominance – occurs when neither

allele is dominant over the other• Heterozygous individuals would show an

intermediate form of BOTH alleles• Ex: Four o’clock flowers• P generation:

Red (RR) x White (WW)• F1 generation:

100% RW = PINK!

Practice incomplete dominance:

• Show the cross of a red flower with a pink flower :

• Genotypes:• Phenotypes:

Practice incomplete dominance:

• Show the cross of two pink flowers:

• Genotypes:• Phenotypes:

Practice incomplete dominance:

• SpongeBob loves growing flowers for his pal Sandy! Her favorite flowers, Poofkins, are found in red, blue, and purple.

• What would happen if SpongeBob crossed a Poofkin with red flowers with a Poofkin with blue flowers.

• R represents a red gene and B represents a blue gene.

II. Codominance• Codominance occurs when BOTH alleles are

dominant and have full effect• Both dominant alleles appear in the

heterozygous individual (NOT BLENDED!)• “Co” = together (think- coworker, cooperate)• Ex: heterozygous chickens speckled black and

white, and roan cows

Practice codominance

• Cattle can be red (RR), white (WW ), or roan (RW = red & white hairs together).

• 1. What would a Punnett square be for a cross of a red cow and a roan cow?

• Give the genotypes and phenotypes

• 2. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?

III. Multiple Alleles• So far, ex. with genes with two alleles (T or t) • Many genes exist in several different forms and are

said to have multiple alleles• Individuals only INHERIT TWO• Ex: coat color in rabbits is controlled by a gene with

FOUR alleles, giving many variations to rabbit’s coat color

• Also, human blood type has 3 alleles: A, B, O

Blood type – multiple alleles

• Blood type exists as four possible phenotypes: A, B, AB, & O.

• There are 3 alleles for the gene that determines blood type–Alleles are: A, B, or O

• Remember: You have just 2 of the 3 in your genotype --- 1 from mom & 1 from dad

Blood type: Codominance and Multiple alleles

Notice that, according to the symbols used in the table above, that the allele for "O" (i) is recessive to the alleles for "A" & "B".

Try a blood type problem:

1. A woman with Type O blood and a man who is Type AB have are expecting a child. What are the possible blood types of their child?

IV. Polygenic Traits• Traits controlled by two or

more genes are said to be polygenic traits. Polygenic means “many genes.”

• Polygenic traits often show a wide range of phenotypes

• Ex: The variety of skin color in humans comes about partly because more than four different genes probably control this trait

IV. Polygenic Traits

• Skin color, hair color, eye color are all polygenic traits (are coded by more than one gene)

• Each of these genes controls the amount of a pigment called melanin

• The more of the genes that are expressed, the darker the color produced.

V. Genes & Environment• Characteristics not ONLY determined by

genes• Genes provide a plan for development, but

how that plan unfolds also depends on the environment

• Ex: temperature affects coloration of many organisms – Siamese cats, western white

butterfly

What type of inheritance is it?