Lecture 12: Chromosomes and DNA Replication for Cell Division

Lecture 12: Chromosomes and DNA Replication for Cell Division DNA – Deoxyribonucleic Acid DNA is condensed to form chromosomes Chromosome  Chromosome number varies among species Humans 46 Domestic dog 78 Leopard frog...

Lecture 12: Chromosomes and DNA Replication for Cell Division DNA – Deoxyribonucleic Acid DNA is condensed to form chromosomes Chromosome  Chromosome number varies among species Humans 46 Domestic dog 78 Leopard frog 26 Fruit fly (Drosophila) 8 Flatworm (Planaria) 16 Potato 48 Yeast 32  Sets of chromosomes Humans have 23 pairs of chromosomes (or 46 total chromosomes) Autosomes – 22 pairs in humans (non-sex chromosomes) Sex chromosomes – 1 pair in humans – XX or XY Dogs have 39 pairs of chromosomes (or 78 total chromosomes) Autosomes – 38 pairs in dogs (non-sex chromosomes) Sex chromosomes – 1 pair in dogs – XX or XY  Homologs In species with two chromosome pairs, the two chromatin that make up the pair are called homologs They are homologous chromosomes Homology any similarity due to common ancestry Autosomes – each homolog nearly identical in size and genetic composition ex: Both carry gene for eye color but one may have brown and the other blue Sex chromosomes – X and Y very different from each other in size and composition X and Y are not considered homologous chromosomes, although they do have short regions of homology  Homolog 1 Homologou s Chromoso Homolog 2 mes Autosomal One homolog was Chromosomes inherited from a maternal donor, and the other from a paternal donor Sex Chromosomes Multicellular organisms: sexual reproduction involves a special kind of cell division (meiosis, which results in gamete formation) n=23 n=23 Zygote: 2n=46 chromosomes ~4 days  Ploidy Levels The haploid number n indicates The number of distinct types of chromosomes present “2 copies” A cell’s ploidy (n, 2n, 3n, etc.) indicates “of each The number of each type of chromosome present chromoso me type” Ploidy Levels n=6 What is the total number of chromosomes? How many of each type do you have? 2n=6 What is the total number of chromosomes? How many of each type do you have?  Ploidy Levels Haploid (or n): Cell with a single pair of every chromosome Human gametes have 1 pair of chromosomes inside them (23 total chromosomes) Diploid (or 2n): A cell with two pairs of every chromosome Humans have 23 pairs of chromosomes (46 total chromosomes) We get one pair from our biological mother and one pair from our biological father Polyploid (or 3n+): Cells with more than two pairs of every chromosome This is not polysomy (like trisomy 21, Down’s syndrome) NOT FOUND IN HUMANS OR ANY MAMMALS Polyploid (Triploid) cells (3n) Polyploidy in humans is lethal  Polyploid (Triploid) cells (3n) Polysomy in chromosome 21 (Trisomy 21)  Life Cycles Sequence of events that produces another generation of organisms For sexually reproducing organisms, involves an alternation between haploid cells or organisms and diploid cells or organisms Three types: Diploid-dominant species Haploid-dominant species Alternation of generations Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 15  Diploid-dominant species Most animal species are diploid Haploid gametes are a specialized type of cell Haploid Dominant Alternation of Generations Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18  Every time a cell divides: 1) its DNA is duplicated, and 2) the DNA divided evenly between parent and daughter cell Introduction to Cell Division Cells come from other cells by division Cell division – replicate genetic material, divide genetic material evenly, form two daughter cells Prokaryotic chromosomes Colorized TEM 32,500 Bacterial cell  Introduction to Cell Division Cells arise through the division of pre- existing cells There are two types of cell division: Mitosis Meiosis Both forms of cell division are accompanied by cytokinesis The cytoplasm of the cell divides into two distinct daughter cells Contrasting Mitosis and Meiosis Meiosis leads to: Production of gametes (eggs and sperm) Daughter cells have half the amount of genetic material as the parent cell We will go into Mitosis leads to: detail on these The production of all other cell types processes in referred to as somatic cells Genetic material is copied and then their own divided equally lectures Daughter cells are genetically identical to the parent cell  Let’s look at some of the functions of cell division in unicellular and multicellular organisms  Single-celled organisms (most): cell division results in asexual reproduction  Multicellular organisms: cell division allows for growth and reproduction (both sexual and asexual)  Multicellular organisms: cell division allows repair of organisms Multicellular organisms: Cell division allows asexual reproduction Asexual reproduction in Hydra  Multicellular organisms: Cell division allows asexual reproduction Asexual reproduction in Mother of Thousands pla  Cell Division Single-celled organisms asexual Multicellular organisms reproduction organism growth repair of organisms. asexual reproduction The Cell Cycle M  Cell Cycle G1 – first gap Interphase S – synthesis of DNA consists of G1, S, and G2 G2 – second gap M – mitosis and cytokinesis G0 – substitutes for G1 for M cells postponing division or never dividing again Gap phases allow the cell to: Grow large enough Synthesize enough organelles for daughter cells  Cell Cycle (Mitosis) G1 phase – The cell grows and cellular contents M (except chromosomes) are duplicated. Prepares to replicate DNA S phase – Each chromosome is replicated (synthesized) G2 phase - Cell synthesizes proteins needed during mitosis and cytokinesis; spindle fibers are formed M phase (Mitosis) - Division of one cell nucleus into two, with separation of sister chromatids Cytokinesis - follows mitosis to divide the cytoplasm into two daughter cells  Every time a cell divides: 1) its DNA is duplicated, and 2) the DNA divided evenly between parent and daughter cell(s)  The Cell Cycle This is where DNA replication happens M DNA Replication ( S-Phase of Cell Division) DNA Replication ( S-Phase of Cell Division) 3’ 5’ DNA Replication ( S-Phase of Cell Division) 3’ Daught 5’ er DNA stand 5’ Daught 3’ er DNA 5’ stand DNA Replication ( S-Phase of Cell Division) DNA Polymerase DNA Replication ( S-Phase of Cell Division) DNA Polymerase Location of a gene = Also called “Homologs” DNA Replication ( S-Phase of Cell Division) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 41  Every time a cell divides: 1) its DNA is duplicated, and 2) the DNA divided evenly between parent and daughter cell Mitosi Meiosi s s The Cell Cycle M This is where cell division happens