Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 8 The Cellular Basis of Reproduction and Inheritance

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rain Forest Rescue Scientists in Hawaii are attempting to "rescue" endangered species from extinction by promoting reproduction Reproduction is one phase of an organism's life cycle – Sexual reproduction Fertilization of sperm and egg produces offspring

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Asexual reproduction Offspring are produced by a single parent, without the participation of sperm and egg Cell division is at the heart of organismal reproduction

CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION 8.1 Like begets like, more or less Asexual reproduction – Chromosomes are duplicated and cell divides – Each daughter cell is genetically identical to the parent and the other daughter Sexual reproduction – Each offspring inherits a unique combination of genes from both parents – Offspring can show great variation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Video: Hydra Budding Video: Hydra Budding

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.2 Cells arise only from preexisting cells "Every cell from a cell" is at the heart of the perpetuation of life – Can reproduce an entire unicellular organism – Is the basis of sperm and egg formation – Allows for development from a single fertilized egg to an adult organism – Functions in an organism's renewal and repair

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.3 Prokaryotes reproduce by binary fission Prokaryotic cells reproduce asexually by a type of cell division called binary fission – Genes are on one circular DNA molecule – The cell replicates its single chromosome – The chromosome copies move apart – The cell elongates – The plasma membrane grows inward, dividing the parent into two daughter cells

LE 8-3a Continued elongation of the cell and movement of copies Duplication of chromosome and separation of copies Plasma membrane Cell wall Prokaryotic chromosome Division into two daughter cells

LE 8-3b Prokaryotic chromosomes Colorized TEM 32,500 

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings THE EUKARYOTIC CELL CYCLE AND MITOSIS 8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division Eukaryotic genes – Many more than in prokaryotes – Grouped into multiple chromosomes in the nucleus

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Eukaryotic chromosomes – Contain a very long DNA molecule associated with proteins – Most of the time occur in the form of thin, loosely packed chromatin fibers – Condense into visible chromosomes just before cell division

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Eukaryotic cell division – Chromosomes replicate Sister chromatids joined together at the centromere – Sister chromatids separate Now called chromosomes – Cell divides into two daughter cells Each with a complete and identical set of chromosomes

LE 8-4b Sister chromatids Centromere TEM 36,600 

LE 8-4c Centromere Chromosome duplication Sister chromatids Chromosome distribution to daughter cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.5 The cell cycle multiplies cells The cell cycle is an ordered series of events extending from the time a cell is formed until it divides into two Most of the cell cycle is in interphase – G1: cell grows in size – S: DNA synthesis (replication) occurs – G2: Cell continues to grow and prepare for division

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The cell actually divides in mitotic (M) phase – Mitosis: nuclear division – Cytokinesis: cytoplasmic division – Duplicated chromosomes evenly distributed into two daughter nuclei

LE 8-5 I NTERPHASE G1G1 G2G2 S (DNA synthesis) Cytokinesis Mitosis M ITOTIC PHASE (M)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.6 Cell division is a continuum of dynamic changes Interphase: Duplication of the genetic material ends when chromosomes begin to become visible Prophase (the first stage of mitosis): The mitotic spindle is forming. Centrosomes migrate to opposite ends of the cell Prometaphase: Chromatins completely coil into chromosomes; nucleoli and nuclear membrane disperse

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Metaphase: The spindle is fully formed; chromosomes are aligned single file with centromeres on the metaphase plate Anaphase: Chromosomes separate from the centromere, dividing to arrive at poles Telophase: Cell elongation continues, a nuclear envelope forms around chromosomes, chromosomes uncoil, and nucleoli reappear Cytokinesis: The cytoplasm divides

LE 8-6a I NTERPHASE P ROPHASE P ROMETAPHASE Kinetochore Fragments of nuclear envelope Centrosome Early mitotic spindle Chromatin Centrosomes (with centriole pairs) LM 250  Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Centromere Spindle microtubules

LE 8-6b M ETAPHASE A NAPHASETELOPHASE AND C YTOKINESIS Metaphase plate Spindle Daughter chromosomes Nuclear envelope forming Cleavage furrow Nucleolus forming

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Video: Animal Mitosis Video: Animal Mitosis Video: Sea Urchin (time lapse) Video: Sea Urchin (time lapse) Animation: Mitosis (All Phases) Animation: Mitosis (All Phases) Animation: Mitosis Overview Animation: Mitosis Overview Animation: Late Interphase Animation: Late Interphase Animation: Prophase Animation: Prophase Animation: Prometaphase Animation: Prometaphase Animation: Metaphase Animation: Metaphase Animation: Anaphase Animation: Anaphase Animation: Telophase Animation: Telophase

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.7 Cytokinesis differs for plant and animal cells Animals – Ring of microfilaments contracts into cleavage furrow – Cleavage occurs Plants – Vesicles fuse into a membranous cell plate – Cell plate develops into a new wall between two daughter cells Animation: Cytokinesis Animation: Cytokinesis

LE 8-7a Cleavage furrow Cleavage furrow Daughter cells Cleavage furrow Contracting ring of microfilaments SEM 140 

LE 8-7b Cell plate forming Wall of parent cell Daughter nucleus New cell wallCell wall TEM 7,500  Daughter cells Vesicles containing cell wall material Cell plate

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.8 Anchorage, cell density, and chemical growth factors affect cell division An organism must be able to control the timing of cell division Anchorage dependence – Most animal cells must be in contact with a solid surface to divide

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density-dependent inhibition – Cells form a single layer – Cells stop dividing when they touch one another – Inadequate supply of growth factor causes division to stop

LE 8-8a Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing (density-dependent Inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition).

LE 8-8b After forming a single layer, cells have stopped dividing. Providing an additional supply of growth factors stimulates further cell division.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.9 Growth factors signal the cell cycle control system The cell cycle control system regulates the events of the cell cycle If a growth factor is not released at three major checkpoints, the cell cycle will stop – G 1 of interphase – G 2 of interphase – M phase

LE 8-9a G 1 checkpoint G0G0 G1G1 G2G2 G 2 checkpoint M checkpoint M S Control system

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings How a growth factor might affect the cell cycle control system – Cell has receptor protein in plasma membrane – Binding of growth factor to receptor triggers a signal transduction pathway Molecules induce changes in other molecules – Signal finally overrides brakes on the cell cycle control system

LE 8-9b G 1 checkpoint G1G1 G2G2 M S Control system Growth factor Plasma membrane Relay proteins Signal transduction pathway Receptor protein

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 8.10 Growing out of control, cancer cells produce malignant tumors Cancer cells do not respond normally to the cell cycle control system – Divide excessively – Can invade other tissues – May kill the organism

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings If an abnormal cell avoids destruction by the immune system, it may form a tumor – Benign: abnormal cells remain at original site – Malignant: abnormal cells can spread to other tissues and parts of the body – Metastasis: spread of cancer cells through the circulatory system

LE 8-10 Tumor Glandular tissue Lymph vessels Blood vessel A tumor grows from a single cancer cell. Cancer cells invade Neighboring tissue. Cancer cells spread through lymph and blood vessels to other parts of the body.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cancers are named according to location of origin – Carcinoma: external or internal body coverings – Sarcoma: tissues that support the body – Leukemia and lymphoma: blood-forming tissues Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.11 Review of the functions of mitosis: growth, cell replacement, and asexual reproduction When the cell cycle operates normally, mitotic cell division functions in – Growth – Replacement of damaged or lost cells – Asexual reproduction Video: Hydra Budding Video: Hydra Budding

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings MEIOSIS AND CROSSING OVER 8.12 Chromosomes are matched in homologous pairs The somatic (body) cells of each species contain a specific number of chromosomes Humans and most other organisms have pairs of homologous chromosomes – Carry genes for the same characteristics at the same place, or locus Except sex chromosomes – One chromosome is inherited from the female parent, one from the male

LE 8-12 Chromosomes Centromere Sister chromatids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.13 Gametes have a single set of chromosomes Diploid cells have two sets of chromosomes (2n) – Somatic cells Haploid cells have one set of chromosomes (n) – Gametes (egg and sperm cells) Sexual life cycles involve the alternation of haploid and diploid stages – Fusion of haploid gametes in fertilization forms a diploid zygote

LE 8-13 Haploid gametes (n  23) Egg cell Sperm cell FertilizationMeiosis Diploid zygote (2n  46) n Multicellular diploid adults (2n  46) Mitosis and development 2n n

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.14 Meiosis reduces the chromosome number from diploid to haploid Meiosis – Like mitosis, is preceded by chromosome duplication – Unlike mitosis, cell divides twice to form four haploid daughter cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The process of meiosis includes two consecutive divisions – Meiosis I In synapsis, homologous chromosomes are paired In crossing over, homologous chromosomes exchange corresponding segments Each homologous pair divides into two daughter cells, each with one set of chromosomes consisting of two chromatids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Meiosis II – Essentially the same as mitosis – Sister chromatids of each chromosome separate – Result is four cells, each with half as many chromosomes as the parent

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Meiosis Overview Animation: Meiosis Overview Animation: Interphase Animation: Interphase Animation: Prophase I Animation: Prophase I Animation: Metaphase I Animation: Metaphase I Animation: Anaphase I Animation: Anaphase I Animation: Telophase I and Cytokinesis Animation: Telophase I and Cytokinesis Animation: Telophase II and Cytokinesis Animation: Telophase II and Cytokinesis Animation: Prophase II Animation: Prophase II Animation: Metaphase II Animation: Metaphase II

LE 8-14a I NTERPHASE P ROPHASE  M ETAPHASE  A NAPHASE  M EIOSIS  Centrosomes (with centriole pairs) Sites of crossing over Spindle Microtubules attached to kinetochore Metaphase plate Sister chromatids remain attached Homologous chromosomes separate Centromere (with kinetochore) Tetrad Sister chromatids Chromatin Nuclear envelope : Homologous chromosome separate

LE 8-14b Cleavage furrow T ELOPHASE  P ROPHASE  M ETAPHASE  A NAPHASE  T ELOPHASE  Sister chromatids separate Haploid daughter cells forming M EIOSIS  : Sister chromatids separate  AND C YTOKINESIS

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.15 Review: A comparison of mitosis and meiosis Mitosis – Provides for growth, tissue repair, and asexual reproduction – Produces daughter cells genetically identical to the parent Meiosis – Needed for sexual reproduction – Produces daughter cells with one member of each homologous chromosome pair

LE 8-15 M ITOSIS M EIOSIS M EIOSIS  M EIOSIS  Prophase Duplicated chromosome (two sister chromatids) Metaphase Anaphase Telophase Parent cell (before chromosome replication) Chromosomes align at the metaphase plate Sister chromatids separate during anaphase Daughter cells of mitosis 2n2n 2n2n n 2n  4 Chromosome replication Chromosome replication Tetrads align at the metaphase plate Homologous chromosomes separate during anaphase  ; sister chromatids remain together No further chromosomal replication; sister chromatids separate during anaphase  nn Daughter cells of meiosis  Daughter cells of meiosis  Site of crossing over Tetrad formed by synapsis of homologous chromosomes Prophase  Metaphase  Anaphase  Telophase  Haploid n  2 n

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Reshuffling of the different versions of genes during sexual reproduction produces genetic variation – Random arrangements of chromosome pairs at metaphase I of meiosis lead to many different combinations of chromosomes – Random fertilization of eggs by sperm greatly increases this variation Animation: Genetic Variation Animation: Genetic Variation

LE 8-16 Possibility 1 Combination 1 Combination 2 Gametes Metaphase  Two equally probable arrangements of chromosomes at metaphase  Possibility 2 Combination 3Combination 4

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.17 Homologous chromosomes carry different versions of genes Each chromosome of a homologous pair can bear different versions of genes at corresponding loci – Makes gametes (and thus offspring) different from one another – Examples: coat color and eye color in mice

LE 8-17a Coat-color genes Eye-color genes Brown Meiosis White Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes Black C E e c C C c c E e E e Pink

LE 8-17b Brown coat (C); black eyes (E)White coat (c); pink eyes (e)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.18 Crossing over further increases genetic variability Crossing over is a genetic rearrangement between two homologous chromosomes – Homologues pair up into a tetrad during prophase I of meiosis – Maternal and paternal chromatids break at the same place – The two broken chromatids join together in a new way at the chiasma Animation: Crossing Over Animation: Crossing Over

LE 8-18a Tetrad Chiasma Centromere TEM 2,200 

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – When homologous chromosomes separate at anaphase I, each contains a new segment – In meiosis II, each sister chromatid goes to a different gamete – Gametes of four genetic types result

LE 8-18b Coat-color genes Eye-color genes ( homologous pair of chromosomes in synapsis) Tetrad Breakage of homologous chromatids Joining of homologous chromatids Chiasma Separation of homologous chromosomes at anaphase  Separation of chromatids at anaphase  and completion of meiosis Parental type of chromosome Recombinant chromosome C C E E e e c c c c e E C CE e e E c C EC c e E C c e Parental type of chromosome Gametes of four genetic types

ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE 8.19 A karyotype is a photographic inventory of an individual's chromosomes A blood sample is treated with a chemical that stimulates mitosis After several days, another chemical arrests mitosis at anaphase, when chromosomes are most highly condensed Chromosomes are photographed and electronically arranged by size and shape into the karyotype Normal humans have 22 pairs of autosomes and two sex chromosomes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

LE 8-19 Packed red and white blood cells Hypotonic solution Centrifuge Blood culture Fluid Fixative White blood cells Stain Centromere Siste r chromatids Pair of homologous chromosomes 2,600 

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 8.20 An extra copy of chromosome 21 causes Down syndrome A person may have an abnormal number of chromosomes Down syndrome is caused by trisomy 21, an extra copy of chromosome 21 – The most common human chromosome number abnormality – Many physical and mental problems – Increased incidence in older mothers

LE 8-20c Infants with Down syndrome (per 1,000 births) Age of mother

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.21 Accidents during meiosis can alter chromosome number Abnormal chromosome count is a result of nondisjunction – The failure of homologous pairs to separate during meiosis I – The failure of sister chromatids to separate during meiosis II

LE 8-21a Number of chromosomes Gametes Normal meiosis  Normal meiosis  Nondisjunction in meiosis  n  1 n  1

LE 8-21b Number of chromosomes Gametes Normal meiosis  Nondisjunction in meiosis  n  1 n  1 n n

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fertilization of an egg resulting from nondisjunction with a normal sperm results in a zygote with an abnormal chromosome number – May be involved in trisomy 21

LE 8-21c Egg cell Sperm cell n (normal) n  1 Zygote 2n  1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 8.22 Abnormal numbers of sex chromosomes do not usually affect survival Nondisjunction can produce gametes with extra or missing sex chromosomes – Upset the genetic balance less than unusual numbers of autosomes – Lead to varying degrees of malfunction in humans – Usually do not affect survival

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8.23 Alterations of chromosome structure can cause birth defects and cancer Breakage can lead to rearrangements affecting genes on one chromosome – Deletion: loss of a fragment of chromosome – Duplication: addition of a fragment to sister chromatid – Inversion: reattachment of a fragment in reverse order – Inversions least harmful because all genes are present in normal number

LE 8-23a Deletion Duplication Inversion Homologous chromosomes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Translocation is the attachment of a chromosomal fragment to a nonhomologous chromosome – Can be reciprocal – May or may not be harmful

LE 8-23b

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chromosomal changes in sperm or egg cells can cause congenital disorders Chromosomal changes in a somatic cell may contribute to the development of cancer

LE 8-23c Reciprocal translocation “Philadelphia chromosome” Activated cancer-causing gene Chromosome 22 Chromosome 9