Introduction to Genetics Heredity and Mendel’s Peas Mrs. Stewart Honors Biology Central Magnet School

Standards: CLE Investigate how genetic information is encoded in nucleic acids. CLE Describe the relationships among genes, chromosomes, proteins, and hereditary traits. CLE Predict the outcome of monohybrid and dihybrid crosses.

Objectives: Differentiate between characteristics and traits Analyze Mendal’s principle of dominance Predict genotype based on phenotype Analyze characteristics and traits in this classroom

Decide with your partner

What is heredity?

Why do family’s look alike?

Heredity & Genetics Heredity - The transmission of characteristics from parents to offspring Genetics – the study of heredity Genes – Segments of DNA that code for a characteristic

Characteristics vs. Traits Characteristic – a heritable feature  Example: flower color, plant height Trait – a genetically determined variant of a characteristic  Example: purple flower color vs white  Now referred to as “Alleles”

Dogs Tell your cats two examples of characteristics that can be inherited from human parents to offspring.

Cats Give your dogs an example of traits/alleles (variations) for the characteristics he/she listed.

Gregor Mendel ( ) “Father of Genetics” Austrian Monk Studied characteristics & traits in pea plants  Have only 7 chromosomes  Can cross pollinate or self pollinate

Gregor Mendel’s Peas “Self pollination”- Pollen from the plant fertilizes its own eggs Similar to asexual reproduction. “True-breeding” - produce identical new plants. “Purebreds”

Mendel’s Peas “Cross-pollination” Remove male parts from true breeding plant, pollinate it with pollen from a plant with different traits. Produce “hybrids” Genetically different

Mendel’s Observations Characteristics Seed shape Seed color Seed coat color Pod shape Pod color Flower position Plant height Traits/Alleles wrinkled or smooth yellow or green white or grey smooth or constricted green or yellow axial or terminal tall or short

Alleles We use letters to represent the different variations Capital Letters = Dominant allele Lowercase letters = recessive allele Example: T = tall plant, t = short plant Most genes have two or more variations (alleles)

Important Vocabulary Terms HETEROzygous: (DIFFERENT)  have different alleles  Example: Tt HOMOzygous : (SAME)  have the same alleles.  Example: TT or tt HYBRID = offspring of heterozygous parents PUREBRED (true- breeding) = offspring of homozygous parents – will produce offspring identical to parent traits

Generations The parent generation The first generation The second generation

Dominance Tall height “masks” the effects of short height. Tall is “dominant”; Short is “recessive”. (P) – Purebred Tall x Purebred Short F1 – All tall (hybrids) F2 – 3:1 ratio tall:short

Principle of Dominance some variations (traits/alleles) are dominant over others Dominant traits will mask or hide the presence of a recessive trait Recessive traits are hidden/masked by a dominant allele

Principle of Dominance – UFC style Only one can win Matt Hughes = Recessive BJ Penn = Dominant

Genotype VS. Phenotype GENOTYPE: actual combination of alleles (genes) inherited from parents.  (One from MOM, and one from DAD.)  Example: Tt, TT or tt PHENOTYPE: physical appearance/expression of the trait.  Example: Tall plant or short plant

Cats and Dogs (think – pair – share) Phenotype Widows Peak or straight hair line Genotype Ww, WW or ww

Cats And Dogs The dominant trait is “gray” fur, and the recessive trait is “white” fur. Lets use the following alleles: Gray is G. White is g. If a bunny is heterozygous gray:  What is the genotype? ______________ If a bunny is homozygous white:  What is the genotype? ______________ If a plant is homozygous gray:  What is the genotype? ______________ Gg gg GG

Principles of Dominance Predictable patterns of dominant and recessive only apply to single gene traits Example: gene for hairline has 2 alleles – widow’s peak (W) or straight hairline (w)  Possible Genotypes: WW, Ww or ww

Dominance VS. Commonality Does dominant mean most commonly occurring? No Examples:  Polydactyl – having 6 fingers  Achondroplasia – Dwarfism  O blood type (recessive)

Group Activity Inventory of Traits

Dogs and Cats Predict you and your partners possible genotypes for the phenotypes listed in traits activity.

Objectives: Differentiate between characteristics and traits Analyze Mendal’s principle of dominance Predict genotype based on phenotype Analyze characteristics and traits in this classroom