Complex Genetics When Mendel ’ s rules don ’ t exactly apply…especially in human traits!

Incomplete Dominance Medium Phenotype When the heterozygote is in between the recessive and dominant.

Problem A red 4 o ’ clock is crossed a pink 4 o ’ clock. What are % of the genotypes and phenotypes of the offspring.

Codominance When both phenotypes are expressed. Use capital letters to represent both genes.

Problem A black cow is mated with a white cow. Both black and white are dominant. What will be the phenotype of the offspring. Show a Punnett Square.

Multiple Alleles When there is more than one allele for a gene. –Blood type –I is dominant –i is recessive –I can be I A or I B

Problem A mother is Blood type A. The father is blood type B. What is their genotypes if they have a child who is blood type O? –A: –B: –O: Punnett Squares to show answer:

Getting Blood!

Blood Types

Sex Linked When a gene is on the female X chromosome. Females get two copies, males only get one. If males have a mutant recessive, they will have the disease.

Example: Colorblindness Rods--Black and White vision Cones--Color Vision Gene for cones on X chromosome –X B X B ; X B X b -Normal Female –X b X b -Colorblind Female –X B Y-Normal Male –X b Y-Colorblind Male

Problem A man is normal vision. His wife is normal vision but her mom was colorblind. What is the chance of their daughters being colorblind? Their sons? Show in a Punnett Square in proper notation.

Polygenic Inheritance Many genes affect a phenotype. Most visual traits have a range. Ex. Eye color, hair color, height

Problem Skin color is influenced by 3 major genes. Dominant genes cause greater production of melanin. Which of the following would be the genotype for a darker skin phenotype? –AABbcc –Aabbcc –AaBbCC

Pleiotropy One mutation has many effects Example--Cystic Fibrosis –What type of mutation? –What are two organ systems that it effects? –Could there be an evolutionary significance to the CF allele?

Epistasis When one gene effects the outcome of another gene. B_E_ : Black fur and black skin B_ee: Yellow fur and black skin bbE_: Brown fur and brown skin Bbee: Yellow fur; brown skin –What does each trait code for? –How does the skin trait affect fur color?

Review: Dihybrid cross How is a dihybrid cross different than a four box Punnett Square? How does the dihybrid Cross show Mendel ’ s Law of Segregation? Law of Indepdent Assortment? Random Fertilization?

Practice Makes Perfect! Mendelian ’ s Law of Dominance –Make your own 5 problems and answer Non-Mendelian Genetics –Worksheets Corn Lab –Lab Notebook!