Genetics Incomplete and Codominant inheritance patterns Work with

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 offspring Heterozygous (Rr and Purple color) ● Then, cross two of the F 1 offspring (Heterozygous) (Rr and Purple color). All F 2 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 Step 2: Set up the box! parents B R = patchwork fish Step 3: Count the number of each phenotype: B B = blue fish R R = red fish What happens when you cross two patchwor k fish? 1/2 will by patchwork, 1/2 will be blue Solv 1: BB 2: BR 1: RR

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 F 1 generation cross, show your work and then complete an F 2 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.

● 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 o The result is the perception of continuous gradation in the expression of these traits. o specialized skin cells produce the pigment, melanin ● Height, skin color and even eye color (recently discovered) ● Example: Skin color o A genotype of AABBCC would express dark skin o 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!