Classical Genetics

Work of Gregor Mendel ( ) In 1843 he entered Monastery of St. Francis in Brünn (Brno) now Czech Republic Served as teacher in church-run school (7th - 9th grade): - Greek - Math & general science About 1854

Monastery and Church in Brno

Mendel and Staff of the Augustinian Monastery c 1865 Mendel Matous Klácel, Fr Npp Fr Napp

Mendel’s Experimental Garden

Mendel’s Experiments: Crossed Pea Varieties with 7 Clearly Distinguishable Traits

Mendel’s First Experiment Crossed Pure Tall x Pure Short (Dwarf) Predictions: The offspring would be: A) All tall B) All short C) All intermediate D) Some would be talls and some short

Mendel’s Experiments (1 & 2) 1st Exp 1st Exp : All offspring (F 1 ) tall! 2nd Exp 2nd Exp: (Bred F1 X F1 and…) Results: Ratio of 787 tall to 277 short (3:1) 1 2

Mendel’s Next (3rd) Experiment Crossed one of the F 1 tall plants with its dwarf parent: F 1 Tall x Dwarf Possible Outcomes: A) All would be tall B) Mixture of Tall & Dwarf Experimental results —> 50% 50%

Mendel’s Law of Dominance These experiments led to an understanding that one trait can mask (or hide) another trait. The trait that comes through is called Dominant. The trait that is masked is called Recessive.

Mendel’s Notational System Used capital letter to denote what he called the dominant form of the trait: T = tall Used lower case letter to denote what he called the recessive trait: t = short (dwarf) Thus for the Tall and Dwarf crosses: TT = Original pure-breeding tall parent is called HOMOZYGOUS Dominant tt = Original pure-breeding short parent is called HOMOZYGOUS Recessive Tt = Hybrid F 1 offspring (HETEROZYGOUS)

Dry Erase Review! Let A = dominant and a = recessive What is the term for AA? What is the term for Aa? What is the term for aa?

More Terminology… Genotype = The letters assigned to represent the alleles. (AA, Aa, aa) Phenotype = The physical trait of the allele. (Black, brown)

Dry Erase Review! Let A = Angry and a = happy Show me... The genotype for happy. Show me…the genotypes for Angry. Show me the phenotype for Aa.

Writing Mendel’s Crosses Using His Notational System (FOIL) How many are tall? How many short? Tt x Tt / \ / \ Gametes T t T t Fertilization TtttTt TT

Mendel’s Law of Segregation We can use FOIL to figure out the genotypic ratio because of Mendel’s Law of Segregation. This Law states that during Meiosis, the alleles will separate from each other. (Homologous pairs separate!)

Dry Erase Review! Let A = Angry and a = happy Use FOIL method to show a cross of AA and Aa. List the genotypic and Phenotypic ratios.

Punnent Square Method Tt T t TT Tt Tt tt What is the genotypic ratio for this cross?

Dry Erase Review! Let A = Angry and a = happy Use Punnent Square method to show a cross of Aa and aa. List the genotypic and Phenotypic ratios.

Dry Erase Review! Let B = Big and b = small Use Punnent Square method to show a cross of Bb and Bb. List the genotypic and Phenotypic ratios.

Tongue Roller R = Tongue Roller r = Unable to Roll Tongue

Widow’s Peak W = Widows Peak w = Lack of Widow’s Peak

Free Ear Lobe Attached Ear Lobe E = Free Ear Lobe e = Attached Ear Lobe

Hitchhiker’s Thumb Hi = Straight Thumb hi = Hitchhiker’s Thumb

Mid-digital Hair M = Mid-Digital Hair m = Absence of Mid-Digital Hair

Dimples D = Dimples d = Absence of Dimples

The Dihybrid Cross He asked what the results would be if he looked at TWO traits at a time He chose two different characteristics of the pea: 1. Seed Coat: Round (dominant) (R) Wrinkled (recessive) (r) 2. Seed color:Yellow (dominant) (Y) Green (recessive) (y)

Results: Pollen Eggs Crossed Two Double Hybrids SsYy x SsYy

Mendel’s Law of Independent Assortment Mendel concluded that during Meiosis, the chromosomes (and alleles on them) will sort out independently of one another. In essence, you can have a mix of dominant and recessive traits!