Lecture #1: chromosomes, genes, dna j chapter 10. z: law of segregation92lzkz zzy z22 l2 gamete formation j. 1880s, flemming observed concept that material outside nucleus becomes organized into visible threads (chromosomes) during cell division. 1903, sutton used sperm cells (spermatogonium) of grasshopper for homologous chromosomes: pairing of homologous chromosomes = tetrads/bivalents, 1st meiotic division separates 2 homologous chromosomes into different cells, mitosis separates 2 chromosomes into 2 cells. kzkz physical carriers of genetic factors (and meiosis is a reductive division) Mutations result in variation in pops j different pops can become genetically different = evolutionary role. Mutations (spontaneous or induced) used for genetic studies j comparing wild type to mutants. Dna = deoxyribonucleic acid, double stranded (2 strands of dna), w/ double helix and 4 different nucleotides. Nucleosides = just a sugar and a base. Nucleotides = a nucleoside w/ 1, 2, or 3 phosphates j a and g = purines (2 rings, bigger), c and t.