Transcript Slide 1
Part II CHROMOSOMES… -complexes of DNA and protein. -Chromosomes are the package for DNA and genes. -duplicated before the cell divides. -chromosome number is specific for each species. A human cell has 46 [or 23 pairs] while a fruit fly has 8 [or 4 pairs]. centromere sister chromatids Cells in the body of sexually producing organisms can be… SOMATIC CELLS -body cells -contain the DIPLOID [2n] chromosome number. -produced through MITOSIS. -examples: muscle cell, nerve cell, stomach cell. GAMETES -sex cells -contain the HAPLOID [n] chromosome number. -produced through MEIOSIS. -examples: sperm cell and egg cell Fertilization restores the diploid number. + Egg is “n” = haploid Sperm is “n” = haploid ZYGOTE is 2n. Repeated mitosis ultimately leads to the development of multicellular organism. A picture of all the chromosomes in a somatic cell is a karyotype. A human karyotype reveals 23 pairs of chromosomes. Each pair is called a homologous pair. The 23rd pair is easy to spot [unequal in size]. They are the sex chromosomes, called X and Y. Organism Organism Human Chromosome # 46 Corn Chromosome # 20 Yeast 32 Onion 16 Cow 60 Lily 24 Dog 78 Donkey 62 Chicken 78 Earthworm 36 Toad 36 Pig 38 CELL CYLE A cell goes through a cell cycle, going through stages of growth and division. Stages of the Cell Cycle 1. Interphase: sometimes called the “resting phase.” This refers to the stage in the life of a cell when it is not dividing. -made up of these sub-stagesa. G1- cells grow in size, cells get ready for DNA synthesis. b. S-phase- DNA replication occurs at this stage. c. G2- cell continues to grow and make proteins. 2. Mitosis: cell divides to produce two daughter cells with the same chromosome number as the parent cell. This stage takes only from 1-2 hours. Important points to remember: a. Chromosomes condense for easy separation [no tangling]. b. Spindle fibers attach to the centromeres, controlling chromosome movement. c. Sister chromatids separate during anaphase. d. Cytokinesis [division of cytoplasm and other cell contents] happen during telophase.