What do you notice about the picture? Incomplete Dominance What do you notice about the picture?

Incomplete dominance is when the two alleles inherited from the parents are neither dominant nor recessive, but blend together to give a physical trait that is somewhere between the two.

The most well-studied example of incomplete dominance in humans occurs in the genes for curly hair. Inheriting a gene for curly hair from one parent and a gene for straight hair from the other parent will give a hair texture that is a blend of the two, wavy hair.

✔Check for Understanding In some flowers (snapdragons), an allele for red flowers when combined with an allele for white flowers will result in pink flowers. Show a cross between a red flower and a white flower.

What percent of the F1 generation will be Red ____________ Pink ____________ White ____________ Next cross two pink flowers, what percentage will be red, pink and white?

Codominance “Co” in front of a word means “together”. Codominance is similar to incomplete dominance because neither allele is fully dominant or recessive. However, where incomplete dominance is a blending of the two alleles, with codominance BOTH alleles are expressed with no blending.

We usually show the alleles (genotype) of codominance as: RR=Red RW=Striped WW=White Both Alleles are Capitalized!

✔Check for Understanding RR=Red RW=Striped WW=White Suppose you own a nursery (green house) and you know striped flowers sell the best and give you the most profits, show the cross that would be necessary to get the MOST striped flowers.

✔Check for Understanding Show what would happen if you crossed two striped flowers below: What would be the phenotypic ratio of the offspring?

The Roan color is the result of crossing a red cow with a white cow The Roan color is the result of crossing a red cow with a white cow. The cross between these two ends up giving the offspring some hairs of each color. Give the genotypes and phenotypes of the cow: Genotype Phenotype RR __________ Rr Red and white ______ White

✔Check for Understanding Predict the phenotypic ratio of a cross between a roan bull and a white cow.

Polygenic Traits Many traits are controlled by more than one gene. These genes may be located on different chromosomes. An example of a trait that is controlled by many genes is eye color.

✔Check for Understanding What are some other polygenic traits in humans that you can think of? 1. ___________________ 2. ___________________ 3. ___________________

Multiple Alleles A number of human traits are the result of more than 2 types of alleles. With multiple alleles there is only one gene for the trait but there are more than two possible alleles.

Example of Multiple Alleles

Blood Type Blood type is an example of a common multiple alleles trait. There are 3 different alleles for blood type, (A, B and O) A is dominant to O. B is dominant to O and AB is codominant These alleles are always on the same chromosome in the same locus. (location)

Blood cont. Blood type genotypes and phenotypes Phenotypes Genotypes O OO A AA or AO B BB or BO AB AB

✔ Let’s Practice You are type O blood and you marry a person with type AB blood. Complete the Punnett Square to show your possible offspring below.

✔ Let’s Practice In the 1950’s, a young woman sued film star/director Charlie Chaplan for parental support for her child. Chaplan’s blood was AB, mother’s was A and the son was O. Complete the Punnett Square for the possible children of Chaplan and the mother.

✔ Let’s Practice The judge ruled in favor of the mother and Charlie Chaplan paid child support. Was the judge correct? _______________ Explain: ____________________________ ____________________________

✔ Let’s Practice Suppose a newborn baby was accidently mixed up in the hospital. DNA testing will take several days and is very expensive. So the nurses have decided to help out by doing a blood test. Baby 1 has blood type O, and baby 2 has blood type A Mr. Smith has type B and Mrs. Smith has type A Mr. Brown has type B and Mrs. Brown has type AB Complete Punnett Squares for each couple and find out who the children belong to. HINT: You may have to do multiple Punnett Squares.

✔ Let’s Practice

✔ Let’s Practice You are type O blood and you marry a person with type AB blood. Complete the Punnett Square to show your possible offspring below.