Presentation on theme: "Part II. CHROMOSOMES… -complexes of DNA and protein. -Chromosomes are the package for DNA and genes. -duplicated before the cell divides. -chromosome."— Presentation transcript:
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]. sister chromatids centromere
Cells in the body of sexually producing organisms can be… SOMATIC CELLS -body cells GAMETES -sex cells -contain the DIPLOID [2n] chromosome number. -produced through MITOSIS. -examples: muscle cell, nerve cell, stomach cell. -contain the HAPLOID [n] chromosome number. -produced through MEIOSIS. -examples: sperm cell and egg cell
Fertilization restores the diploid number. Sperm is n = haploid + ZYGOTE is 2n. Egg is n = haploid Repeated mitosis ultimately leads to the development of multi- cellular 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 23 rd pair is easy to spot [unequal in size]. They are the sex chromosomes, called X and Y.
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-stages- a. G 1 - cells grow in size, cells get ready for DNA synthesis. b. S-phase- DNA replication occurs at this stage. c. G 2 - 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.