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Cell Reproduction Chromosomes • rod-like structures made of DNA and protein 2 Kinds of proteins in chromosomes A. histones- proteins that DNA wraps around, helps hold shape of chromosome and allows DNA to pack tightly B. nonhistones- Do not aid in packing of DNA, instead they control specific regions of the DNA Chromosomes • Chromosomes consist of two identical halves (each half is called a chromatid) • Chromatids form when DNA makes a copy of itself prior to cell division • When the cell divides each new cell receives one chromatid Chromosomes • Chromatids are held together by a centromere Chromosomes • Prokaryote DNA consists of a single chromosome that is attached to inside of cell membrane Chromosome Number • Each species has a characteristic number of chromosomes in each cell Ex: Humans 46 Dogs 78 Adder’s tongue fern 1,262 Chromosome # has nothing to do with complexity of organism Types of Chromosomes 1. Sex chromosomes- determine sex of organism (could carry other genes as well) -Human sex chromosomes are either X or Y Females XX Males XY Types of Chromosomes 2. Autosomes- all other chromosomes in an organism -Of the 46 human chromosomes, 2 are sex chromosomes, the other 44 are autosomes Types of Chromosomes • Every cell of an organism produced by sexual reproduction has 2 copies of each autosome (one from each parent) • The two copies of each chromosome are called homologous chromosomessame shape and size and carry genes for same trait Karyotypes • Picture of an individual’s chromosomes (cells are treated with chemicals to start mitosis, photos are taken during metaphase, and pictures are cut out and matched up) Diploid vs. Haploid Cells • Diploid cells- cells with two sets of chromosomes (2n) • Diploid cells have both chromosomes for each pair as well as the sex chromosomes • Diploid cells in humans have 23 pairs, or 46 chromosomes 2n = 46 Diploid vs. Haploid Cells • Human gametes, or sex cells, are haploid sperm- male gamete egg- female gamete • Haploid cells contain only one set of chromosomes, n • Have half the # of chromosomes as diploid cells and only have one sex chromosome Diploid vs. Haploid Cells • When sperm and egg unite during fertilization, first cell of new organism will be diploid (2n) • If gametes were not haploid, the new cell would be 4n and not functional Cell Division in Prokaryotes • Binary fission- Division of prokaryotes into two identical offspring cells 3 Stages 1. Chromosome makes a copy of itself 2. Cell grows until approximately 2X size of original 3. Cell wall forms between two chromosomes forming 2 new identical cells Cell Division in Eukaryotes • Cell Cycle- events that make up the life of a cell 2 Main Parts: A. Interphase-cell growth and DNA replication B. Mitosis- nuclear and cytoplasmic division Interphase • most of cell’s time spent in this part of cycle A. G1- cell grows in size and carries on metabolism B. S- DNA is copied C. G2- cell grows some more and prepares to divide • *Some cells enter G0 phase where they remain and no longer grow or divide (Ex: nerve cells) Mitosis 4 Stages of Mitosis 1. 2. 3. 4. Prophase Metaphase Anaphase Telophase Prophase • first and longest stage of mitosis • chromatin coils into rod-shaped chromosomes • Nucleus disappears • Centrioles move to opposite ends of cell • Spindle begins to form Metaphase • double chromosomes become attached to spindle by centromere • chromosomes line up on mid-line or equator of cell Anaphase • sister chromatids separate and move to opposite poles of cell Telophase • • • • final stage of mitosis chromosomes reach opposite poles spindle disassembles nuclear envelope reappears and nucleolous forms Cytokinesis • Cytoplasm divides **Different between plant and animal cells In animal cells, cell membrane pinches in midway between two poles creating a cleavage furrow Cytokinesis • In plant cells, vesicles formed by golgi fuse together at mid-line forming a cell plate **Each cell formed by mitosis receives an exact copy of original cell’s chromosomes and approximately half of the parent cell’s cytoplasm and organelles.