Chapter 13 Genetics I. Mendelian Genetics: A. Mendel and his work: - Founded by Gregor Mendel an Austrian monk who first published his results in 1866. His results were appreciated 35 years later in 1901 when they were rediscovered by three scientists independently.

Experiments with garden peas: Mendel did crosses between true-breeding garden peas. In monohybrid crosses, two parents are crossed that differ in one form of a trait (e.g. tall and short; green and yellow pods). The first generation (F1) resembled one of the two parents (dominant form). Crosses between plants of the first generation produced the second generation (F2). In F2 the progeny segregated 75% dominant : 25% recessive. This result led Mendel to the first law of inheritance "law of segregation" which means that: Any trait in an individual is represented by two factors. During the formation of gametes the two factors segregate unchanged so that a gamete will carry only one of the two factors.

- In dihybrid crosses, Mendel crossed two parent plants one was true breeding for two dominant traits and the other was true breeding for two recessive traits. From F2 results he deduced his second law of inheritance which is "law of independent assortment" which means that: The two factors of each of trait segregate independently from two factors of any other trait during the formation of gametes. A gamete carries only one factor for every trait.

Terms to be familiar with: - Dominant (A is dominant to a) - Recessive (a is recessive to A) - Homozygous (true-breeding) AA or aa - Heterozygous (mixed) Aa - Genotype - Phenotype - Complete dominance

Incomplete dominance: occurs when each of the two forms (alleles) of a trait (gene) contribute to the phenotype in a heterozygous individual. Example is the inheritance of the color of flower in snapdragons.

B. Linkage 1. Tendency of genes on same chromosome to be inherited together 2. Crossing-over C. Chromosomal Mapping 1. Locus of gene 2. Map distance D. Hardy-Weinberg Law 1. Specifies criteria for genetic equilibria in large populations 2. Conditions altering equilibrium a. Nonrandom breeding b. Gene mutation c. Selection

III. Molecular Genetics A. Structure of DNA 1. Nucleotides a. Nitrogenous base b. 5-carbon sugar c. Phosphate group 2. Nitrogenous bases a. Purines, adenine and guanine (2 linked rings) b. Pyrimidines, cytosine and thymine (single ring)

B. Replication (Duplication) of DNA C. RNA and Synthesis of Proteins D. Specific Types of RNA and Their Functions 1. Messenger RNA (mRNA) 2. Ribosomal RNA (rRNA) 3. Transfer RNA (tRNA) E. The Mechanism of Gene Expression 1. Transcription 2. Translation 3. The Nature of Mutations F. How Do Genes Produce Phenotypes?