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 IA or IB

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– XBXB; XBXb-Normal

Female

– XbXb-Colorblind Female

– XBY-Normal Male

– XbY-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!