chapter 3 to 4

• Reproduction is essential for life
• Each organism exists solely because its ancestors succeeded in producing progeny that could develop, survive, and reach reproductive age
• Reproduction


  At its most basic level, involves a single cell reproducing itself
• For a unicellular organism

  Cellular reproduction also reproduces the organism
• For multicellular organisms


  Cellular reproduction is involved in growth, repair, and the formation of sperm and egg cells that enable the organism to reproduce
• At the molecular level, reproduction


  Involves the cell's unique capacity to manipulate large amounts of DNA, DNA's ability to replicate, and DNA's ability to carry information that will determine the characteristics of cells in the next generation
• Genetics


  The study of how biological information is transmitted from one generation to the next
• Modern molecular genetics


  Provides biochemical explanations of how this information is expressed in an organism
• Information carried in DNA


  Is manifested in the kinds of proteins that exist in each individual
• Proteins


  Contribute to observable traits, such as eye color and hair color, and they function as enzymes that regulate the rates of chemical reactions in organisms
• Within certain environmental limits, animals are what they are by the proteins that they synthesize
• At the level of the organism, reproduction


  Involves passing DNA from individuals of one generation to the next generation
• The classical approach to genetics

  Involves experimental manipulation of reproduction and observing patterns of inheritance between generations
• This work began with Gregor Mendel (1822–1884), and it continues today
• DNA


  The genetic material, and it exists with protein in the form of chromosomes in eukaryotic cells
• Chromatin


  The highly dispersed state of chromosomes during most of the life of a cell
• Genes


  Units of inheritance that may actively participate in the formation of protein during the dispersed state of chromosomes
• Chromosomes


  Exist in a highly folded and condensed state that allows them to be distributed between new cells being produced during cell division
• Heterochromatic regions


  Inactive portions of chromosomes that produce dark banding patterns with certain staining procedures
• Euchromatic regions


  Active portions of chromosomes
• James D. Watson and Francis Crick, 1968
• Sex chromosomes


  Chromosomes that are represented differently in females than in males and function in sex determination
• Autosomes


  Chromosomes that are alike and not involved in determining sex
• 1. O system


  The simplest system for determining sex because it involves only one kind of chromosome
• 1. Y system


  The system of sex determination where males are usually XY and females are XX
• In birds, the sex chromosomes are designated Z and W, and the female is ZW
• Even though the X and Y chromosomes are called "sex chromosomes," they also help determine non-sex-related traits
• Chromosome number


  Varies greatly among species, usually between 10 and 50
• N


  The number of different kinds of chromosomes in a set
• Diploid


  Having two sets, or 2N chromosomes
• Haploid


  Having only one set, or N chromosomes (like gametes)
• Polyploidy


  Having more than the diploid number of chromosomes
• Asexual reproduction often accompanies polyploidy
• Cell cycle


  The life of a cell, from its beginning until it divides to produce the new generation of cells
• Mitosis


  The distribution of chromosomes between two daughter cells
• Cytokinesis


  The partitioning of the cytoplasm between the two daughter cells
• Interphase


  The time between the end of cytokinesis and the beginning of the next mitotic division, a time of cell growth, DNA synthesis, and preparation for the next mitotic division
• G1 phase


  The early growth phase of the cell
• S phase


  The phase where growth continues and DNA replication occurs
• G2 phase


  The phase that prepares the cell for division, including replication of organelles, synthesis of microtubules and proteins for the mitotic spindle, and chromosome condensation