Modern BiologyPages 144 - 147 Chromosome Structure • Eukaryotic cells have their DNA in structures called chromosomes. A cell’s chromosomes
Modern BiologyPages 144 - 147 Chromosome Structure • If the nucleus of your cell is the size of a basketball, the DNA would be 40 miles long! E. coli “spills” it’s DNA
Modern BiologyPages 144 - 147 Chromosome Structure • Chromosomes: • Contains a single DNA molecule. • Have the DNA wrapped around proteins called histones. Chromosome structure
Modern BiologyPages 144 - 147 Chromosome Structure • Chromosomes condense only for cell reproduction. • Condensation: • Twist • Become shorter • Become thicker • Become visible • Chromosomes can be moved about cell easier. Chromosome condensation
Modern BiologyPages 144 - 147 Chromosome Structure • Prior to cell reproduction chromosomes replicate. • Each copy is called a chromatid. • Sister chromatids are connected by a centromere Centromere
Modern BiologyPages 144 - 147 Chromosome Numbers • Each species has characteristic number of chromosomes. • Humans = 46 • Fruit flies = 8 • Crayfish = 200 • Chimpanzee = 48 Fruit fly chromosomes
Modern BiologyPages 144 - 147 Chromosome Numbers • Chromosomes are arranged in pairs called homologous pairs.
Wednesday 12/3Pages 144 - 147 Chromosome Numbers • One pair determines sex: sex chromosomes. • All others are called autosomes.
Modern BiologyPages 144 - 147 Sex Chromosomes • Either X or Y. • XX creates female. • XY creates male. Sex Chromosomes
Modern BiologyPages 144 - 147 Haploid Vs Diploid • A karyotype shows all homologous pairs matched on a sheet. • Sex chromosomes are paired separately Human female karyotyes
Name two materials that make up chromosomes. • Histones and DNA. • What structure connects chromatids once the DNA (chromosome) has replicated? • Centromere • What term describes all chromosomes in a cell that are identical in males and females? • Autosomes • What term describes the pair of chromosomes that are different in males and females? • Sex chromosomes • What does the term “haploid” tell you about a cell? Diploid? • One of each chromosome pair. • Homologous pairs of chromosomes.
Modern BiologyPages 144 - 147 Haploid Vs Diploid • All cells except gametes have pairs of chromosomes. • Diploid • Sperm and egg (gametes) have one of each pair. • haploid Human sperm at the surface of an egg
Modern BiologyPages 148 - 149 Cell Division • All cells are derived from division of pre-existing cells. • Cell division is different in prokaryotes and eukaryotes. Prokaryotic cell reproducing
Modern BiologyPages 148 - 149 Cell Division in Prokaryotes • Prokaryotes reproduce by binary fission. • Steps in prokaryote binary fission. • Chromsome replicates • Cell grows • New cell wall develops • Cell splits into two cells Binary Fission
Modern BiologyPages 148 - 149 Cell Division in Eukaryotes • Two types of cell division: • Mitosis: Results in two daughter cells identical to the original mother cell. • Meiosis: Production of sperm and egg with 1/2 the chromosomes. Mitosis in eukaryotic cells
Modern BiologyPages 148 - 149 Cell Cycle • G1 Phase • Cell growth, normal activity • S Phase • Replication of DNA • G2 Phase • Growth for cell reproduction. • Mitosis • Cytokinesis Eukaryotic cell cycle
Modern BiologyPages 148 - 149 Interphase • Consists of G1, S, G2. • Cell spends most time in interphase. • Cells may enter G0 phase. • Do not reproduce. Interphase
Modern BiologyPages 148 - 149 Stages of Mitosis • Preparation of the nucleus for binary fission. • Continuous process divided into four stages. Cells in phases of mitosis
Modern BiologyPages 148 - 149 Stages of Mitosis • Prophase • DNA shortens and thickens. • Two centrosomes appear with two centrioles. • Nuclear envelope breaks down. • Centrioles move to opposite poles. • Spindle fibers are produced. Cells in prophase
Modern BiologyPages 148 - 149 Stages of Mitosis • Metaphase • Chromosmes are moved to center of cell. • Kinetichore fibers move chromosomes. • Fibers are connected to kinetichore. • Polar fibers run from centrosome to centrosome. Metaphase
Modern BiologyPages 148 - 149 Stages of Mitosis • Anaphase • Centromere splits. • Chromosomes separate. • Each copy moves to opposite pole. Anaphase
Modern BiologyPages 148 - 149 Stages of Mitosis • Telophase • Chromosomes become long and slender. • New nuclear envelope forms. • Nucleolus forms. • Spindle fibers breakdown. Telophase
Friday 12/5Pages 148 - 149 Plant Vs Animal Mitosis Plant Interphase Animal Interphase
Friday 12/5Pages 148 - 149 Plant Vs Animal Mitosis Plant Prophase Animal Prophase
Friday 12/5Pages 148 - 149 Plant Vs Animal Mitosis Plant Metaphase Animal Metaphase
Friday 12/5Pages 148 - 149 Plant Vs Animal Mitosis Plant Anaphase Animal Anaphase
Friday 12/5Pages 148 - 149 Plant Vs Animal Mitosis Plant Telophase Animal Telophase
Meiosis • Meiosis is a process by which the chromosome number is reduced by half. • Only occurs in testes and ovaries. • Only occurs in cells called “germ” cells. • Used to produce sperm and eggs.
Meiosis (cont) • Chromosomes in all cells of all organisms are in pairs referred to as homologous pairs. • These pairs must be split during the process of meiosis
Prior to the Process Meiosis • Cells undergo the phases G1, S, & G2 prior to meiosis. • Cells that undergo meiosis start as diploid (2n) cells. • Meiosis results in four haploid (1n) cells being produced.
Meiosis is known as “reduction and division” • Chromosomes # is reduced from 2n to 1n. • Divisions of the cell result in 4 cells being produced.
A diploid cell (2n) has a pair of each chromosome. • These pairs are referred to as homologous. • One “homologue” of a pair came from mom and the other from dad.
After meiosis is complete only one of each type of chromosome is present in a sperm or egg.
Meiosis I • Prophase I • Homologous pairs align with each other. • Synapsis occurs. • Synaptonemal complex holds homologues in place. • Crossing over occurs. (At chiasma)
Meiosis I • Metaphase I • Microtubules attach only to outside kinetochores. • Homologous pairs move to equator of cell due to kinetochore fibers.
Meiosis I • Anaphase I • Homologues are pulled apart by kinetochore fibers. • Homologous pairs are separated and moved to opposite poles.
Meiosis I • Telophase I • Cell goes through cytokinesis. • Cells are now 1n or haploid.
Meiosis II • Prophase II • No replication • No synapsis • No crossing over.
Meiosis II Centromeres eventually split. • Chromosomes are moved to poles of cell. A second division occurs.
Crossing Over • Crossing over occurs during tetrad positioning of chromosomes. • Results in genetic recombination
Crossing Over • Actual picture of chromosomes crossing over. • This creates variation among offspring of a species.
Mitosis Occurs each time a “body cell” replicates Homologues are randomly distributed across metaphase plate Crossing over never occurs. Sister chromatids remain identical. Sister chromatids separate in anaphase I. Meiosis Occurs only in germ cells of ovaries and testes. Homologous pairs align (synapsis) Crossing over occurs. Sister chromatids are genetically different Sister chromatids do not separate in anaphase I Contrasting Mitosis & Meiosis