Dominant/Recessive Clarification: Genes are not recessive or dominant. Alleles of genes are not recessive or dominant. The proteins made by alleles of genes are not recessive or dominant. You cannot tell if a trait is recessive or dominant based on the genes that affect it or the alleles in a population.

Recessive Recessive traits are just traits caused by an allele that can be masked or hidden. Recessive traits are only visible in an organism if the organism is homozygous for the allele that causes the trait. Recessive traits are frequently less common in a population...but not always!

Dominant Traits Dominant traits are usually more visible in an organism, even if the organism is heterozygous and only has one allele that causes that trait. Dominant traits are typically not masked or hidden. Dominant traits can be caused by heterozygous or homozygous sets of alleles.

Test If a trait can disappear and reappear from generation to generation in a population, then IT IS RECESSIVE. This is the ONLY WAY TO TELL FOR SURE. Example: Sometimes brown eyed parents can have a blue eyed child. Since the child has a trait not visible in the parents, that trait (blue eyes) is recessive.

Incomplete Dominance This is when: an allele for a gene causes a visible effect or trait in an organism that is visible… While a different allele that causes a different effect is also visible… Causing the organism to have a mix or blend of the two traits.

Incomplete Dominance So if there is a dominant trait of redness… And a dominant trait of whiteness… Together they will create an incompletely dominant trait of pinkness.

Once again… You cannot tell if a trait is dominant or recessive or incompletely dominant just by looking at the trait or allele or gene. It is the pattern of inheritance in a population that let us know if a trait is recessive.

Quiz 1 Construct a Punnett Square for a cross between a homozygous recessive individual and a heterozygous individual.

This is an allele for a gene that contributes to petal color This is an allele for a gene that contributes to petal color. This particular allele encodes the information to build a protein that makes a red pigment. R   This is an allele for a gene that contributes to petal color. This particular allele encodes the information to build a protein that makes a blue pigment. B This is an allele for a gene that contributes to petal color. This particular allele encodes the information to build a non-functioning protein that does nothing. r