Incomplete and Co-dominant inheritance patterns Genetics Incomplete and Co-dominant inheritance patterns

Work with a partner and answer the following: · Do you think twins could be born of two different color skins? If yes, how do you think this can happen and if no, why could this not happen?

Intermediate Patterns of Inheritance

Review: Complete Dominance Mendel experiments showed the following: One homozygous recessive (rr and white color) X homozygous dominant (RR and purple color) = All off offspring Heterozygous (Rr and Purple color) Then, cross two of the F1 offspring (Heterozygous) (Rr and Purple color). All F2 offspring show 3:1 phenotypic ratio or 1:2:1 genotypic ratio Well, this is not always the case….

Incomplete dominance A form of inheritance in which the heterozygous alleles are both expressed, resulting in a combined phenotype. Think: Blending Example: Flowers

Recap We have examined complete dominance, in which one allele is clearly dominant over the other incomplete dominance, in which neither allele dominates over the other. In a third type of dominance, codominance, both alleles are expressed in the phenotype of individuals that have heterozygous alleles.

Codominance In a certain fish, blue scales and red scales are codominant. When a fish has the genotype B R, it has a patchwork of blue and red scales. What happens if you breed this fish with a fish that only has Blue Scales. Step 1: Determine the genotypes of the parents B R = patchwork fish B B = blue fish R R = red fish Step 2: Set up the box! Step 3: Count the number of each phenotype: What happens when you cross two patchwork fish? 1/2 will by patchwork, 1/2 will be blue 1: BB 2: BR 1: RR Solve?

Multiple Alleles- Three or more alleles for a particular gene Great Example: Human Blood Type 3 Alleles for the 1 gene that determines your blood type (Remember you only have 2 of the 3 alleles- one from each parent) Four possible phenotypes

One more example- Work with a partner and solve the following problem: Genotype: Phenotype Blood type A: IA IA Blood type B: IBIB Blood type AB: IAIB What is the probability of having a child with a different genotype, if mother has type A blood type and father has type B blood type? Be sure to include genotypes and phenotypes in your work: Complete an F1 generation cross, show your work and then complete an F2 cross. Show your work Answer: genotype and phenotype ratio both 1:2:1

red blood cells have special markers called antigens Type AB has both antigens,

Color Blindness- How is this inherited? Work with a partner and think of possible two reasons of how a person could inherit color blindness? List two challenges an individual could face if color blind.

Sex-linked Traits “Gender” Gender determined from Dad, because mom will always supply an X Sex-linked Traits “Gender” 50% chance of being male or 50% chance of being female

What does it mean to have a sex-linked trait? If the gene is recessive, then males only need one such recessive gene to have a sex-linked trait rather than the customary two recessive genes for traits that are not sex-linked. This is why males exhibit some traits more frequently than females.

So...Henry the VIII Decapitated Anne Boleyn because no male heirs….

Sex-Linked Example: Hemophilia genetic disorder, impair the body's ability to control blood clotting recessive, What does that mean? .

Polygenic Traits Trait controlled by more than one gene The result is the perception of continuous gradation in the expression of these traits. specialized skin cells produce the pigment, melanin Height, skin color and even eye color (recently discovered) Example: Skin color A genotype of AABBCC would express dark skin A genotype of aabbcc would express light skin

Test Cross Test crosses involve breeding the individual in question with another individual that expresses a recessive version of the same trait. Test cross = the cross of an organism with an unknown dominant genotype with an organism that is homozygous recessive for that trait If all offspring display the dominant phenotype, the individual in question is homozygous dominant if the offspring display both dominant and recessive phenotypes, than the individual is heterozygous.

Guinea Pig Test Cross I hand you a black Guinea pig (BB or Bb) and ask you, what is the genotype? Preform a test cross to identify genotype of the black Guinea pig. To perform an actual test cross with this guinea pig, we would need a guinea pig (of the opposite sex) that is homozygous recessive ("bb").  In other words, we would need a white guinea pig to mate with our black guinea pig.  Work both crosses to determine genotype!