The Cellular Basis of Reproduction and Inheritance Chapter 8 The Cellular Basis of Reproduction and Inheritance

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

Cell division is at the heart of organismal reproduction 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

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

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

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

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

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

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 Chromosome duplication Sister chromatids Centromere Chromosome distribution to daughter cells

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

The cell actually divides in mitotic (M) phase Mitosis: nuclear division Cytokinesis: cytoplasmic division Duplicated chromosomes evenly distributed into two daughter nuclei

S (DNA synthesis) Cytokinesis Mitosis INTERPHASE G1 G2 MITOTIC LE 8-5 PHASE (M)

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

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 LM 250  INTERPHASE PROPHASE PROMETAPHASE Early mitotic spindle Fragments of nuclear envelope Centrosomes (with centriole pairs) Centrosome Chromatin Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Centromere Spindle microtubules

LE 8-6b Metaphase plate Cleavage furrow Nucleolus forming Nuclear ANAPHASE TELOPHASE AND CYTOKINESIS Metaphase plate Cleavage furrow Nucleolus forming Nuclear envelope forming Daughter chromosomes Spindle

Animation: Cytokinesis 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

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

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

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

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).

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

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 G1 of interphase G2 of interphase M phase

G0 S G1 G2 M LE 8-9a G1 checkpoint Control system M checkpoint

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

Growth factor Plasma membrane Relay proteins Receptor protein LE 8-9b Growth factor Plasma membrane Relay proteins Receptor protein G1 checkpoint Signal transduction pathway Control system G1 S M G2

8.10 Growing out of control, cancer cells produce malignant tumors 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

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 Lymph vessels Tumor Blood vessel Glandular tissue 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.

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

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

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

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 (2n = 46) Haploid gametes (n = 23) n Egg cell n Sperm cell Meiosis Fertilization Diploid zygote (2n = 46) 2n Multicellular diploid adults (2n = 46) Mitosis and development

8.14 Meiosis reduces the chromosome number from diploid to haploid Like mitosis, is preceded by chromosome duplication Unlike mitosis, cell divides twice to form four haploid daughter cells

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

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

LE 8-14a Microtubules attached to kinetochore Centrosomes MEIOSIS I : Homologous chromosome separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Microtubules attached to kinetochore Centrosomes (with centriole pairs) Metaphase plate Sister chromatids remain attached Sites of crossing over Spindle Nuclear envelope Sister chromatids Tetrad Centromere (with kinetochore) Homologous chromosomes separate Chromatin

LE 8-14b Haploid daughter Sister chromatids cells forming separate MEIOSIS I : Sister chromatids separate TELOPHASE I TELOPHASE I PROPHASE I METAPHASE I ANAPHASE I AND CYTOKINESIS AND CYTOKINESIS Cleavage furrow Sister chromatids separate Haploid daughter cells forming

8.15 Review: A comparison of mitosis and meiosis 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

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

Animation: Genetic Variation 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

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

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

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

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

Animation: Crossing Over 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

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

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 C E (homologous pair of c e Tetrad (homologous pair of chromosomes in synapsis) c e Breakage of homologous chromatids C E c e Joining of homologous chromatids C E Chiasma c e Separation of homologous chromosomes at anaphase I C E C e c E c e Separation of chromatids at anaphase II and completion of meiosis C E Parental type of chromosome C e Recombinant chromosome c E Recombinant chromosome 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 Hypotonic Fixative Packed red and solution white blood cells Stain Centrifuge Blood culture Fluid Centromere Sister chromatids Pair of homologous chromosomes 2,600

8.20 An extra copy of chromosome 21 causes Down syndrome 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

Infants with Down syndrome LE 8-20c 90 80 70 60 Infants with Down syndrome (per 1,000 births) 50 40 30 20 10 20 25 30 35 40 45 50 Age of mother

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

Nondisjunction in meiosis I Normal meiosis II Normal meiosis II LE 8-21a Nondisjunction in meiosis I Normal meiosis II Normal meiosis II Gametes n + 1 n + 1 n  1 n  1 Number of chromosomes

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

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 n + 1 Sperm cell Zygote 2n + 1 n (normal)

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

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

Homologous chromosomes LE 8-23a Deletion Duplication Homologous chromosomes Inversion

Translocation is the attachment of a chromosomal fragment to a nonhomologous chromosome Can be reciprocal May or may not be harmful

LE 8-23b

Chromosomal changes in sperm or egg cells can cause congenital disorders Chromosomal changes in a somatic cell may contribute to the development of cancer

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