Notes: Genetics continued Essential Question: What is the difference between incomplete and co-dominant traits?

Review from genetics Different forms of a genes are alleles. The principal of dominance states that some alleles are dominant and others are recessive. Heterozygous genotypes always shows the dominant trait.

What is INCOMPLETE DOMINANCE? Neither allele is dominant in expressing its trait. Each allele is represented by a different letter. Heterozygous forms will be expressed as a blend of the homozygous traits.

Example of incomplete dominance In some plants the alleles for flower color show incomplete dominance RR = Red flowers WW = White flowers RW = Pink flowers

Straight Curly Wavy SC SS CC Practice problem Straight hair and curly hair are incomplete dominant and people who are heterozygous have wavy hair. What are the genotypes for each trait if S is the allele for straight and C is the allele for curly? Straight Curly Wavy SC SS CC

SC SC CC CC C C S SC C Practice problem CC SC CC Set up the punnett square for a wavy haired woman to marry a curly haired man. CC wavy haired woman: ______ curly haired man: ______ SC C C CC SC SC S SC CC CC C

SC SC CC CC C C S SC C 0 % 50 % 50 % Practice problem CC Based on the Punnet square what percentage of the offspring have: Straight hair: ______ Curly hair: _____ Wavy hair: _____ CC 0 % 50 % C C 50 % SC SC S SC CC CC C

How does incomplete dominance work in humans? SICKLE CELL ANEMIA Homozygous Dominant (AA) –Normal Heterozygous (Aa) –Partial Disease Homozygous Recessive (aa) –Disease Being heterozygous is a benefit because it protects them from malaria

- In the heterozygous form, both traits appear together. What is codominance? - “co”-together (cooperate-work together, cohabitate-live together) - In the heterozygous form, both traits appear together.

Examples of Codominance

Example of codominance in humans: Blood Types Humans have 4 blood types: A, B, AB, O Only 3 alleles: A,B,O Alleles A and B are codominant. Allele O is recessive.

A IAIA or IAIO B IBIB or IBIO AB IAIB O IOIO Blood type Chart Phenotype Genotype A IAIA or IAIO B IBIB or IBIO AB IAIB O IOIO

IAIB IA IB IAIO IBIO IO IOIO IO IAIO IBIO Practice Problem IOIO IAIB Dad has type O and mom has type AB. Set up the punnett square. IAIB Dad genotype = ______ Mom genotype = ______ IA IB IOIO IAIB IAIO IBIO IO IOIO IO IAIO IBIO

Exit Ticket: COPY DOWN AND FILL IN THE SENTENCE BELOW: In simple dominance the heterozygous genotype shows the __________ trait. This is different from incomplete and codominance because in incomplete dominance the heterozygous trait shows a ____________ between the dominant and recessive traits, while in codominance ______ traits are show.