Incomplete Dominance and Codominance Thursday, October 20, 2011

Simple Dominance Dominant: An organism with a dominant allele for a trait will ALWAYS have that trait.

Simple Dominance Dominant: An organism with a dominant allele for a trait will ALWAYS have that trait. Recessive: An organism with a recessive allele for a trait will only show that form when the organism is homozygous recessive (has 2 recessive alleles).

Examples of Simple Dominance Pumpkin shape: W = warty w = smooth

Examples of Simple Dominance Pumpkin shape: W = warty w = smooth Which allele is dominant, warty or smooth?

Examples of Simple Dominance Pumpkin shape: W = warty w = smooth Which allele is recessive, warty or smooth?

Examples of Simple Dominance Pumpkin shape: W = warty w = smooth What is the genotype of a pumpkin that is homozygous recessive?

Examples of Simple Dominance Pumpkin shape: W = warty w = smooth What is the genotype of a pumpkin that is heterozygous for pumpkin shape?

Examples of Simple Dominance Pumpkin shape: W = warty w = smooth What is the phenotype of a pumpkin that has the genotype WW?

Examples of Simple Dominance Pumpkin shape: W = warty w = smooth What is the phenotype of a pumpkin that has the genotype Ww?

Examples of Simple Dominance Pumpkin shape: W = warty w = smooth What is the phenotype of a pumpkin that has the genotype ww?

Examples of Simple Dominance W w w w

Examples of Simple Dominance W w w Ww ww Ww ww w

Examples of Simple Dominance What is the probability that these two pumpkins will have a warty baby pumpkin? W w w Ww ww Ww ww w

Examples of Simple Dominance What is the probability that these two pumpkins will have a warty baby pumpkin? W w w Ww ww 75% Ww ww w

Simple dominance is not the whole story… Some alleles are neither DOMINANT or RECESSIVE and some traits are controlled by multiple alleles or multiple genes.

Simple dominance is not the whole story… INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. Think blend in.

Simple dominance is not the whole story… INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. Think blend in The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes.

Simple dominance is not the whole story… INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes. We use two capital letters, since neither letter is completely dominant or completely recessive.

Simple dominance is not the whole story… INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes. We use two capital letters, since neither letter is completely dominant or completely recessive. Example: Blending colors.

Simple dominance is not the whole story… INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes. We usually use two capital letters, since neither letter is completely dominant or completely recessive. Example: Blending colors. W = white petals R = red petals RR WW

Simple dominance is not the whole story… INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes. We usually use two capital letters, since neither letter is completely dominant or completely recessive. Example: Blending colors. WW = white petals RR = red petals WR = pink petals WR or RW

Simple dominance is not the whole story… INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes. We usually use two capital letters, since neither letter is completely dominant or completely recessive. Example: Blending colors. Note: Testmakers sometimes use one letter instead of two! RR ww Rr

Simple dominance is not the whole story… INCOMPLETE DOMINANCE: When one allele is not completely dominant over the other. The HETEROZYGOUS phenotype is somewhere in-between the two homozygous phenotypes. We usually use two capital letters, since neither letter is completely dominant or completely recessive. Example: Blending colors. Note: Testmakers sometimes use one letter instead of two! The trick is to see if the heterozygous genotype has a “new” blended phenotype. RR ww Rr

Let’s practice!

Simple dominance is not the whole story… CODOMINANCE: When both alleles show up (neither allele is recessive). Think together.

Simple dominance is not the whole story… CODOMINANCE: When both alleles affect the phenotype (appearance). Example: Spots of both colors, blood type, sickle cell disease.

Codominance RR = red WW = white RW or WR = red and white spotted