What is Genetics? What is Genetics? A. Gregor Mendel – Father of Genetics • Discovered the basic principles of heredity from his analysis of crosses using garden peas • He was the first to integrate science and math What is Genetics? B. Alleles = Traits • Mendel reasoned traits are controlled by 2 factors known today as alleles of a gene • Diploid organisms have two alleles for every gene • Alleles are passed sexually & asexually • Variation arises during sexual reproduction where offspring receives different alleles than either of the parents What is Genetics? C. Mendel’s Laws 2. Law of Segregation • Members of each pair of alleles separate when gametes are formed • A gamete will receive one allele or the other, but not both What is Genetics? C. Mendel’s Laws 1. Law of Independent Assortment • 2 or more pairs of alleles segregate independently of one another during meiosis gamete formation • This applies to traits on different pairs of chromosomes or ones that are not close together What is Genetics? II. Genes –History of the gene 1. Wilhelm Johansen • Coined the term “gene” 2. Walter Sutton • Genes on chromosomes 3. Thomas Morgan • Verified Sutton’s work using Drosophilae (Fruit fly) 1 What is Genetics? B. Genes are segments of DNA molecules located on a chromosome 1. Carry instructions for producing a specific trait 2. Diploid organisms have two alleles for each gene • Asexual reproduction: offspring receives both alleles from one parent cell • Sexual reproduction: offspring receive one allele from one parent and the second allele from a different parent What is Genetics? 2. Only one allele of gene can be expressed in an organism a. Dominant allele: is the allele of a trait that will be expressed • Represented by a capital letter (Example: “G”) What is Genetics? • Incomplete Dominance: where alleles for a trait are neither dominant nor recessive. This causes a mixing of a trait expression • Co-dominance: both alleles are expressed fully (Example: AB Blood Type) What is Genetics? C. Which allele of a 1. Each individual has two gene is expressed in factors, or alleles, for a diploid organism? each trait, which may or may not have the same information • Homozygous: the pair of alleles for a gene are identical (Example: GG or gg) • Heterozygous: the pair of alleles for a gene are different (Gg) What is Genetics? b. Recessive allele: is the allele of a trait that will be hidden unless it is homozygous • Represented by a lower case letter (Example: “g”) • This is why you can be a carrier for a genetic disorder and not know it What is Genetics? 3. Genotype: the actual allele pair for a gene • We use symbols to represent the genotype • GG – homozygous dominate • Gg – heterozygous (the dominant or capital letter will be expressed) • gg – homozygous recessive 2 What is Genetics? 4. Phenotype: the physical expression of a trait or the physical appearance • GG – Yellow plants • Gg – Yellow plants • gg – Green plants What is Genetics? D. Mendel’s Experiments and Punnet Square 1. P1: (Parent Generation) • Purple (WW) x White (ww) 2. F1: 1st Filial Generation • All offspring were purple (Ww) 3. F2: 2nd Filial Generation • 3 plants were purple and 1 plant was white What is Genetics? 4. Punnett Squares • • A mathematical model used to predict the results of a cross Steps for a Punnett square: a. Define what the letters mean – W = Purple and w = white b. Tell what is being crossed – WW x ww c. Punnett Square d. Data table – Genotype % and Phenotype % 3