Incomplete Dominance

Co-dominanceMultiple AllelesSex-linked Traits

Incomplete DominanceO Shows a blend of both traits if both

are presentO Neither trait is dominant O Creates a “blend” of the two traits

O Like mixing paint

Incomplete Dominance Example

O In Four o’clock flowers the alleles for flower color are both equal therefore neither dominates over the other. Instead, they blend to create pink flowers if both genes are present. Show a cross between a red four o’clock flower (RR) and a white flower (WW).

Let’s try one:O In humans straight hair (SS) and

curly hair (CC) are traits that have incomplete dominance, that result in hybrids who have wavy hair (SC). Cross a curly hair female with a wavy haired male.

O In andalusian chickens, gray is a blend of pure black with pure white. Cross a gray rooster with a gray hen. Give the genotypes and phenotypes of their offspring.

Co-dominanceO Shows both traits if they are present

O Like co-authors (both names appear on the cover)

O Like co-captains (both people are captains)

O Problems are done the same way as incomplete dominance problems

O Only difference would be how you would see it in person

Co0dominance ExampleO In cattle, neither red (RR) nor white

(WW) hair dominates. Instead, both show up if present to make a “color” called roan (RW). Show the cross between a roan bull and a roan cow.

Multiple AllelesO In humans, there are four types of

blood; type A, type B, type AB, and type O. The alleles A and B are co-dominant to each other and the O allele is recessive to both A and B alleles.

O Blood Type (Phenotype)GenotypeO Type A IAIA or IAiO Type B IBIB or IBiO Type AB IAIB (example of Co-

Dominance)

O Type O ii

Blood Type ExampleO A man with blood type AB marries a woman

with type O blood. Show the possible genotypes and phenotypes for their children.

Let’s try one:O A woman with Type A blood and a

man with Type AB blood have a baby. The woman is suing the man for child support, but he is refusing to pay because he says the baby (who has Type O blood) is not his. Is he right or should he be paying child support? Use a Punnett Square to prove your answer.

O An extremely rich elderly couple died in a car accident. They had no known living relatives. A man shows up claiming to be their long lost son. The elderly couple both had Type AB blood. The man claiming to be their son has Type O blood. Does this man have a claim to their fortune? Use a Punnett Square to support your answer.

Sex-linked TraitsO In humans sex is determined by the twenty third pair of

chromosomes known as “sex chromosomes”.O If you have two x-shaped (XX) chromosomes you are

destined to be a female.O If you have an x and a Y-shaped (XY) chromosomes

you are destined to be a male.O Since the X and Y chromosomes carry different

information, any genes found on the X chromosomes are referred to as sex-linked genes.

O Therefore, women will have two alleles for these genes because they have two (XX) chromosomes. On the other hand, men have only one allele for each of these genes because they have only one X chromosome (XY).

Sex-linked Traits Example

O In fruit flies, the gene for eye color is carried on the X chromosome, which is a sex chromosome (sex-linked). The allele for red eyes is dominant over the allele for white eyes. If a white-eyed female fruit fly is mated with a red-eyed male, predict the possible offspring.

Let’s try one:O Hemophilia is a sex-linked trait. A person with

hemophilia is lacking certain proteins that are necessary for normal blood clotting. Hemophilia is caused by a recessive allele so use “N” for normal and “n” for hemophilia. Since hemophilia is sex-linked, remember a woman will have two alleles (NN or Nn or nn) but a man will have only one allele (N or n). A woman who is heterozygous (a carrier) for hemophilia marries a normal man. Give the genotype and phenotype ratios along with your Punnett Square.

O In canaries, the green variety with black eyes is dependent upon a dominant sex-linked factor (B), the cinnamon variety with brown eyes is due to its recessive allele (b). A cinnamon male is mated to a homozygous green female. Show all work and ratios.