Work of Gregor Mendel Section 11-1 Pages Standard IV Objective 2a: Explain Mendel’s laws of segregation and independent assortment and their role in genetic inheritance.

Genetics Vocabulary Trait: specific characteristic Trait: specific characteristic Gene: sequence of DNA that codes for a protein thus determining a trait Gene: sequence of DNA that codes for a protein thus determining a trait Alleles: different forms of a gene Alleles: different forms of a gene

Gregor Mendel Gregor Mendel—father of genetics Gregor Mendel—father of genetics Conducted his work in the garden Conducted his work in the garden of a monastery—changed biology forever Worked with true breeding pea plants Worked with true breeding pea plants True breeding—produce identical offspring if allowed to self-pollinate True breeding—produce identical offspring if allowed to self-pollinate He looked at 7 different traits He looked at 7 different traits

Alleles Where do living organisms get alleles from? Where do living organisms get alleles from? Organisms receive one allele for each trait from each parent. Organisms receive one allele for each trait from each parent. Principle of Dominance: some alleles are dominant and other are recessive Principle of Dominance: some alleles are dominant and other are recessive If a dominant allele is present, the organism will take on the characteristic of the dominant allele. If a dominant allele is present, the organism will take on the characteristic of the dominant allele. PTC paper PTC paper

Alleles Representing different alleles Representing different alleles T (capital letter) = dominant trait T (capital letter) = dominant trait t (lower case) = recessive trait t (lower case) = recessive trait For each trait there are two alleles (one from each parent) For each trait there are two alleles (one from each parent) Example: Plant height Example: Plant height TT and Tt TT and Tt tt tt

Probability Principle of Probability: used to predict outcomes of genetic crosses Principle of Probability: used to predict outcomes of genetic crosses Homozygous – 2 identical alleles Homozygous – 2 identical alleles Homozygous dominant (TT) Homozygous dominant (TT) Homozygous recessive (tt) Homozygous recessive (tt) Heterozygous – 2 different alleles (Tt) Heterozygous – 2 different alleles (Tt)

Mendel’s Crosses Original pair of plants—P (parental) generation Original pair of plants—P (parental) generation The offspring of the P generation are called the F 1 generation The offspring of the P generation are called the F 1 generation The offspring of the F 1 generation are called the F 2 generation The offspring of the F 1 generation are called the F 2 generation Hybrid—the offspring of crosses between parents with different traits Hybrid—the offspring of crosses between parents with different traits

Results of Crosses Mendel took the true breeding plants with contrasting characteristics and crossed them. Mendel took the true breeding plants with contrasting characteristics and crossed them. Tall plant x Short plant Tall plant x Short plant Took it another step: he allowed all hybrid plants to produce an F2 generation by self-pollination Took it another step: he allowed all hybrid plants to produce an F2 generation by self-pollination

Genetic Vocabulary Heterozygous—organisms that have two different alleles for the same trait Heterozygous—organisms that have two different alleles for the same trait Homozygous—organisms that have two identical alleles for a particular trait Homozygous—organisms that have two identical alleles for a particular trait Genotype—genetic makeup (TT, Tt, tt) Genotype—genetic makeup (TT, Tt, tt) Phenotype—physical characteristics (the plant is tall or the plant is short) Phenotype—physical characteristics (the plant is tall or the plant is short)

Punnett Squares Dad is heterozygous for a particular trait Dad is heterozygous for a particular trait Mom is homozygous recessive for the same trait Mom is homozygous recessive for the same trait What is the projected outcome of this cross? What is the projected outcome of this cross?

Ratios Genotypic Ratio Genotypic Ratio How many of each genotype do I have? How many of each genotype do I have? Do not reduce ratio!!! Do not reduce ratio!!! H.D.:H.:H.R. H.D.:H.:H.R. Ex. 1:2:1 Ex. 1:2:1 Must add up to total number of boxes Must add up to total number of boxes Phenotypic Ratio Phenotypic Ratio How may of each phenotype do I have? How may of each phenotype do I have? Is the plant tall or short? Is the plant tall or short? Ex. 3:1 Ex. 3:1

Picture Credits u.jpg u.jpg u.jpg u.jpg arents_images/resources_parents_help.jpg arents_images/resources_parents_help.jpg arents_images/resources_parents_help.jpg arents_images/resources_parents_help.jpg albums/b268/plopperscioly/punnettsquare.jpg&imgrefurl= albums/b268/plopperscioly/punnettsquare.jpg&imgrefurl= albums/b268/plopperscioly/punnettsquare.jpg&imgrefurl= albums/b268/plopperscioly/punnettsquare.jpg&imgrefurl= g g g g