CHAPTER 8 The Cellular Basis of Reproduction and Inheritance Modules 8.1 – 8.3

Parents Reproduction Inheritance Cell Cycle Cell Division Life cycle Daughter

Parents Asexual Reproduction Inheritance Mitosis Cell Division Cell Cycle Sexual Meiosis Daughter

8.1 Like begets like, more or less Some organisms make exact copies of themselves, asexual reproduction

8.2 Cells arise only from preexisting cells All cells come from cells Cellular reproduction is called cell division Cell division allows an embryo to develop into an adult It also ensures the continuity of life from one generation to the next

8.3 Prokaryotes reproduce by binary fission Prokaryotic cells divide asexually These cells possess a single chromosome, containing genes The chromosome is replicated The cell then divides into two cells, a process called binary fission Prokaryotic chromosomes Figure 8.3B

Binary fission of a prokaryotic cell Plasma membrane Prokaryotic chromosome Cell wall Duplication of chromosome and separation of copies Continued growth of the cell and movement of copies Division into two cells Figure 8.3A

THE EUKARYOTIC CELL CYCLE AND MITOSIS 8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division A eukaryotic cell has many more genes than a prokaryotic cell The genes are grouped into multiple chromosomes, found in the nucleus The chromosomes of this plant cell are stained dark purple Figure 8.4A

Chromosome distribution to daughter cells When the cell divides, the sister chromatids separate Chromosome duplication Two daughter cells are produced Each has a complete and identical set of chromosomes Sister chromatids Centromere Chromosome distribution to daughter cells Figure 8.4C

8.5 The cell cycle multiplies cells The cell cycle consists of two major phases: Interphase, where chromosomes duplicate and cell parts are made The mitotic phase, when cell division occurs Figure 8.5

8.6 Cell division is a continuum of dynamic changes Eukaryotic cell division consists of two stages: Mitosis Cytokinesis

Centrosomes (with centriole pairs) Early mitotic spindle Centrosome INTERPHASE PROPHASE Centrosomes (with centriole pairs) Early mitotic spindle Centrosome Fragments of nuclear envelope Kinetochore Chromatin Centrosome Spindle microtubules Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Figure 8.6

TELOPHASE AND CYTOKINESIS METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Cleavage furrow Nucleolus forming Metaphase plate Nuclear envelope forming Spindle Daughter chromosomes Figure 8.6 (continued)

8.7 Cytokinesis differs for plant and animal cells In animals, cytokinesis occurs by cleavage This process pinches the cell apart Cleavage furrow Cleavage furrow Contracting ring of microfilaments Figure 8.7A Daughter cells

In plants, a membranous cell plate splits the cell in two Cell plate forming Wall of parent cell Daughter nucleus In plants, a membranous cell plate splits the cell in two Cell wall New cell wall Vesicles containing cell wall material Cell plate Daughter cells Figure 8.7B

8.9 Growth factors signal the cell cycle control system Proteins within the cell control the cell cycle Signals affecting critical checkpoints determine whether the cell will go through a complete cycle and divide G1 checkpoint Control system M checkpoint G2 checkpoint Figure 8.9A

Cancer cells have abnormal cell cycles 8.10 Connection: Growing out of control, cancer cells produce malignant tumors Cancer cells have abnormal cell cycles They divide excessively and can form abnormal masses called tumors Radiation and chemotherapy are effective as cancer treatments because they interfere with cell division

Malignant tumors can invade other tissues and may kill the organism Lymph vessels Tumor Glandular tissue Metastasis 1 A tumor grows from a single cancer cell. 2 Cancer cells invade neighboring tissue. 3 Cancer cells spread through lymph and blood vessels to other parts of the body. Figure 8.10

Parents Asexual Reproduction Inheritance Mitosis Cell Division Cell Cycle Sexual Meiosis Daughter

8.12 Chromosomes are matched in homologous pairs MEIOSIS AND CROSSING OVER 8.12 Chromosomes are matched in homologous pairs Somatic cells of each species contain a specific number of chromosomes Human cells have 46, making up 23 pairs of homologous chromosomes Chromosomes Centromere Sister chromatids Figure 8.12

Multicellular diploid adults (2n = 46) Mitosis and development The human life cycle Haploid gametes (n = 23) Egg cell Sperm cell MEIOSIS FERTILIZATION Diploid zygote (2n = 46) Multicellular diploid adults (2n = 46) Mitosis and development Figure 8.13

MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Spindle attached to homologous chromosomes Centrosomes (with centriole pairs) Sites of crossing over Metaphase plate Sister chromatids remain attached Spindle Nuclear envelope Chromatin Sister chromatids Tetrad Centromere Homologous chromosomes separate Figure 8.14, part 1

MEIOSIS II: Sister chromatids separate TELOPHASE I AND CYTOKINESIS TELOPHASE II AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II Cleavage furrow Sister chromatids separate Haploid daughter cells forming Figure 8.14, part 2

PARENT CELL (before chromosome replication) Site of crossing over MITOSIS MEIOSIS PARENT CELL (before chromosome replication) Site of crossing over MEIOSIS I PROPHASE PROPHASE I Tetrad formed by synapsis of homologous chromosomes Duplicated chromosome (two sister chromatids) Chromosome replication Chromosome replication 2n = 4 Chromosomes align at the metaphase plate Tetrads align at the metaphase plate METAPHASE METAPHASE I ANAPHASE I TELOPHASE I ANAPHASE TELOPHASE Sister chromatids separate during anaphase Homologous chromosomes separate during anaphase I; sister chromatids remain together Haploid n = 2 Daughter cells of meiosis I 2n 2n No further chromosomal replication; sister chromatids separate during anaphase II MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II Figure 8.15

Two equally probable arrangements of chromosomes at metaphase I Meiosis produces genetic variations : Independent orientation of chromosomes POSSIBILITY 1 POSSIBILITY 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Gametes Combination 1 Combination 2 Combination 3 Combination 4 Figure 8.16

C E C E C E c e c e c e Coat-color genes Eye-color genes Brown Black White Pink Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes Figure 8.17A, B

Crossing over during prophase I of meiosis Tetrad Chaisma Centromere Figure 8.18A

How crossing over leads to genetic recombination Coat-color genes Eye-color genes How crossing over leads to genetic recombination Tetrad (homologous pair of chromosomes in synapsis) 1 Breakage of homologous chromatids 2 Joining of homologous chromatids Chiasma Separation of homologous chromosomes at anaphase I 3 Separation of chromatids at anaphase II and completion of meiosis 4 Parental type of chromosome Recombinant chromosome Recombinant chromosome Parental type of chromosome Figure 8.18B Gametes of four genetic types

ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE 8.19 A karyotype is a photographic inventory of an individual’s chromosomes To study human chromosomes microscopically, researchers stain and display them as a karyotype A karyotype usually shows 22 pairs of autosomes and one pair of sex chromosomes

Preparation of a karyotype Fixative Packed red And white blood cells Hypotonic solution Blood culture Stain White Blood cells Centrifuge 3 2 1 Fluid Centromere Sister chromatids Pair of homologous chromosomes 4 5 Figure 8.19

8.20 Connection: An extra copy of chromosome 21 causes Down syndrome This karyotype shows three number 21 chromosomes An extra copy of chromosome 21 causes Down syndrome Figure 8.20A, B

The chance of having a Down syndrome child goes up with maternal age Figure 8.20C

8.21 Accidents during meiosis can alter chromosome number Abnormal chromosome count is a result of nondisjunction Either homologous pairs fail to separate during meiosis I Nondisjunction in meiosis I Normal meiosis II Gametes n + 1 n + 1 n – 1 n – 1 Number of chromosomes Figure 8.21A

Or sister chromatids fail to separate during meiosis II Normal meiosis I Nondisjunction in meiosis II Gametes n + 1 n – 1 n n Number of chromosomes Figure 8.21B

Fertilization after nondisjunction in the mother results in a zygote with an extra chromosome Egg cell n + 1 Zygote 2n + 1 Sperm cell n (normal) Figure 8.21C

8.22 Connection: Abnormal numbers of sex chromosomes do not usually affect survival Nondisjunction can also produce gametes with extra or missing sex chromosomes Unusual numbers of sex chromosomes upset the genetic balance less than an unusual number of autosomes

Table 8.22

A man with Klinefelter syndrome has an extra X chromosome Poor beard growth Breast development Under- developed testes Figure 8.22A

A woman with Turner syndrome lacks an X chromosome Characteristic facial features Web of skin Constriction of aorta Poor breast development Under- developed ovaries Figure 8.22B

8.23 Connection: Alterations of chromosome structure can cause birth defects and cancer Chromosome breakage can lead to rearrangements that can produce genetic disorders or cancer Four types of rearrangement are deletion, duplication, inversion, and translocation

Homologous chromosomes Deletion Duplication Homologous chromosomes Inversion Reciprocal translocation Nonhomologous chromosomes Figure 8.23A, B

Chromosomal changes in a somatic cell can cause cancer A chromosomal translocation in the bone marrow is associated with chronic myelogenous leukemia Chromosome 9 Reciprocal translocation Chromosome 22 “Philadelphia chromosome” Activated cancer-causing gene Figure 8.23C

Parents Asexual Reproduction Inheritance Mitosis Cell Division Cell Cycle Sexual Meiosis Daughter