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The Cellular Basis of Reproduction and Inheritance

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

2 Rain Forest Rescue Scientists in Hawaii
Have attempted to “rescue” endangered species from extinction

3 The goals of these scientists were
To promote reproduction to produce more individuals of specific endangered plants Cyanea kuhihewa Kauai, Hawaii

4 In sexual reproduction
Fertilization of sperm and egg produces offspring In asexual reproduction Offspring are produced by a single parent, without the participation of sperm and egg

8.1 Like begets like, more or less Some organisms reproduce asexually And their offspring are genetic copies of the parent and of each other LM 340 Figure 8.1A

6 Other organisms reproduce sexually Creating a variety of offspring
Figure 8.1B

7 8.2 Cells arise only from preexisting cells
Cell division is at the heart of the reproduction of cells and organisms Because cells come only from preexisting cells

8 8.3 Prokaryotes reproduce by binary fission
Prokaryotic cells Reproduce asexually by cell division Colorized TEM 32,500 Prokaryotic chromosomes Figure 8.3B

9 Division into two daughter cells
As the cell replicates its single chromosome, the copies move apart And the growing membrane then divides the cells Plasma membrane Prokaryotic chromosome Cell wall Duplication of chromosome and separation of copies 1 Continued elongation of the cell and movement of copies 2 Division into two daughter cells 3 Figure 8.3A

8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division A eukaryotic cell has many more genes than a prokaryotic cell And they are grouped into multiple chromosomes in the nucleus

11 And are visible only when the cell is in the process of dividing
Individual chromosomes contain a very long DNA molecule associated with proteins And are visible only when the cell is in the process of dividing If a cell is not undergoing division Chromosomes occur in the form of thin, loosely packed chromatin fibers LM 600 Figure 8.4A

12 Before a cell starts dividing, the chromosomes replicate
Producing sister chromatids joined together at the centromere TEM 36,000 Centromere Sister chromatids Figure 8.4B

13 Chromosome distribution to daughter cells
Cell division involves the separation of sister chromatids And results in two daughter cells, each containing a complete and identical set of chromosomes Centromere Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Figure 8.4C

14 8.5 The cell cycle multiplies cells
The cell cycle consists of two major phases INTERPHASE S (DNA synthesis) G1 G2 Cytokinesis Mitosis MITOTIC PHASE (M) Figure 8.5

15 During interphase Chromosomes duplicate and cell parts are made During the mitotic phase Duplicated chromosomes are evenly distributed into two daughter nuclei

16 8.6 Cell division is a continuum of dynamic changes
In mitosis, after the chromosomes coil up A mitotic spindle moves them to the middle of the cell

17 The sister chromatids then separate
And move to opposite poles of the cell, where two nuclei form Cytokinesis, in which the cell divides in two Overlaps the end of mitosis

18 The stages of cell division
INTERPHASE PROPHASE PROMETAPHASE LM 250 Chromatin Centrosomes (with centriole pairs) Nucleolus Nuclear envelope Plasma membrane Early mitotic spindle Centrosome Centromere Chromosome, consisting ot two sister chromatids Spindle microtubules Kinetochore Fragments of nuclear envelope Figure 8.6 (Part 1)

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Daughter chromosomes Nuclear envelope forming Cleavage furrow Nucleolus forming Figure 8.6 (Part 2)

20 8.7 Cytokinesis differs for plant and animal cells
In animals Cytokinesis occurs by a constriction of the cell (cleavage) Cleavage furrow SEM 140 Daughter cells Contracting ring of microfilaments Figure 8.7A

21 A membranous cell plate splits the cell in two
In plants A membranous cell plate splits the cell in two TEM 7,500 Cell plate forming Wall of parent cell Daughter nucleus Cell wall New cell wall Vesicles containing cell wall material Cell plate Daughter cells Figure 8.7B

22 8.8 Anchorage, cell density, and chemical growth factors affect cell division
Most animal cells divide Only when stimulated, and some not at all

23 In laboratory cultures
Most normal cells divide only when attached to a surface They continue dividing Until they touch one another 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). Figure 8.8A

24 Are proteins secreted by cells that stimulate other cells to divide
Growth factors Are proteins secreted by cells that stimulate other cells to divide After forming a single layer, cells have stopped dividing. Providing an additional supply of growth factors stimulates further cell division. Figure 8.8B

25 8.9 Growth factors signal the cell cycle control system
A set of proteins within the cell Controls the cell cycle

26 Signals affecting critical checkpoints in the cell cycle
Determine whether a cell will go through the complete cycle and divide Control system G1 S G2 M G1 checkpoint G2 checkpoint M checkpoint G0 Figure 8.9A

27 Is usually necessary for cell division.
The binding of growth factors to specific receptors on the plasma membrane Is usually necessary for cell division. Control system G1 S G2 M G1 checkpoint Plasma membrane Growth factor Receptor protein Relay proteins Signal transduction pathway Figure 8.9B

28 8.10 Growing out of control, cancer cells produces malignant tumors
CONNECTION 8.10 Growing out of control, cancer cells produces malignant tumors Cancer cells divide excessively to form masses called tumors

29 Can invade other tissues
Malignant tumors Can invade other tissues Tumor 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. Lymph vessels Blood vessel Figure 8.10

30 Radiation and chemotherapy
Are effective as cancer treatments because they interfere with cell division

31 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 LM 500 Figure 8.11A

32 Replacement of damaged or lost cells
LM 700 Figure 8.11B

33 Asexual reproduction LM 10 Figure 8.11C

8.12 Chromosomes are matched in homologous pairs The somatic (body) cells of each species Contain a specific number of chromosomes For example human cells have 46 Making up 23 pairs of homologous chromosomes

35 The chromosomes of a homologous pair
Carry genes for the same characteristics at the same place, or locus Chromosomes Centromere Sister chromatids Figure 8.12

36 8.13 Gametes have a single set of chromosomes
Cells with two sets of chromosomes Are said to be diploid Gametes, eggs and sperm, are haploid With a single set of chromosomes

37 Involve the alternation of haploid and diploid stages
Sexual life cycles Involve the alternation of haploid and diploid stages Mitosis and development Multicellular diploid adults (2n = 46) Diploid zygote (2n = 46) 2n Meiosis Fertilization Egg cell Sperm cell n Haploid gametes (n = 23) Figure 8.13

38 8.14 Meiosis reduces the chromosome number from diploid to haploid
Meiosis, like mitosis Is preceded by chromosome duplication But in meiosis The cell divides twice to form four daughter cells

39 The first division, meiosis I
Starts with synapsis, the pairing of homologous chromosomes In crossing over Homologous chromosomes exchange corresponding segments Meiosis I separates each homologous pair And produce two daughter cells, each with one set of chromosomes

40 Meiosis II is essentially the same as mitosis
The sister chromatids of each chromosome separate The result is a total of four haploid cells

41 MEIOSIS I: Homologous chromosomes separate
The stages of meiosis MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Centrosomes (with centriole pairs) Sites of crossing over Spindle Microtubules attached to kinetochore Metaphase plate Sister chromatids remain attached Nuclear envelope Chromatin Sister chromatids Tetrad Centromere (with kinetochore) Homologous chromosomes separate Figure 8.14 (Part 1)

42 MEIOSIS II: Sister chromatids separate
PROPHASE II METAPHASE II ANAPHASE II TELOPHASE I AND CYTOKINESIS TELOPHASE II AND CYTOKINESIS Cleavage furrow Haploid daughter cells forming Sister chromatids separate MEIOSIS II: Sister chromatids separate Figure 8.14 (Part 2)

43 8.15 Review: A comparison of mitosis and meiosis
Parent cell (before chromosome replication) Chromosome replication Chromosomes align at the metaphase plate Tetrads align at the metaphase plate Sister chromatids separate during anaphase Homologous chromosomes separate during anaphase I; sister chromatids remain together No further chromosomal replication; sister chromatids separate during anaphase II Prophase Metaphase Anaphase Telophase Duplicated chromosome (two sister chromatids) Daughter cells of mitosis 2n Daughter cells of meiosis I n 2n = 4 Tetrad formed by synapsis of homologous chromosomes Meiosis i Meiosis ii Prophase I Metaphase I Anaphase I Telophase I Haploid n = 2 Daughter cells of meiosis II Figure 8.15

44 8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring Each chromosome of a homologous pair Differs at many points from the other member of the pair

45 Two equally probable arrangements of chromosomes at metaphase I
Random arrangements of chromosome pairs at metaphase I of meiosis Lead to many different combinations of chromosomes in eggs and sperm Combination 1 Combination 2 Combination 3 Combination 4 Gametes Metaphase II Two equally probable arrangements of chromosomes at metaphase I Possibility 1 Possibility 2 Figure 8.16

46 Random fertilization of eggs by sperm
Greatly increases this variation

47 8.17 Homologous chromosomes carry different versions of genes
The differences between homologous chromosomes Are based on the fact that they can bear different versions of a gene at corresponding loci Tetrad in parent cell (homologous pair of duplicated chromosomes) e c E C White Pink Meiosis Black Brown Chromosomes of the four gametes Eye-color genes Coat-color genes Brown coat (C); black eyes (E) White coat (C); pink eyes (e) Figure 8.17B Figure 8.17A

48 8.18 Crossing over further increases genetic variability
Genetic recombination Which results from crossing over during prophase I of meiosis, increases variation still further Chiasma Tetrad Centromere TEM 2,200 Figure 8.18A

49 Tetrad (homologous pair of chromosomes in synapsis)
How crossing over leads to genetic variation Coat-color genes Eye-color genes C E Tetrad (homologous pair of chromosomes in synapsis) c e Breakage of homologous chromatids 1 C E c e Joining of homologous chromatids 2 C E Chiasma c e 3 Separation of homologous chromosomes at anaphase I C E C e c E c e 4 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 Figure 8.18B Gametes of four genetic types

8.19 A karyotype is a photographic inventory of an individual’s chromosomes A karyotype Is an ordered arrangement of a cell’s chromosomes

51 Preparation of a karyotype from a blood sample
Blood culture Fluid Centrifuge Packed red and white blood cells Hypotonic solution Fixative White blood cells Stain Centromere Pair of homologous chromosomes Sister chromosomes 2,600X A blood culture is centrifuged to separate the blood cells from the culture fluid. 1 The fluid is discarded, and a hypotonic solution is mixed with the cells. This makes the red blood cells burst. The white blood cells swell but do not burst, and their chromosomes spread out. 2 Another centrifugation step separates the swollen white blood cells. The fluid containing the remnants of the red blood cells is poured off. A fixative (preservative) is mixed with the white blood cells. A drop of the cell suspension is spread on a microscope slide, dried, and stained. 3 The slide is viewed with a microscope equipped with a digital camera. A photograph of the chromosomes is entered into a computer, which electronically arranges them by size and shape. 4 The resulting display is the karyotype. The 46 chromosomes here include 22 pair of autosomes and 2 sex chromosomes, X and Y. Although difficult to discern in the karyotype, each of the chromosomes consists of two sister chromatids lying very close together (see diagram). 5 Figure 8.19

52 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 Which causes problems

53 Down syndrome is caused by trisomy 21 An extra copy of chromosome 21
5,000 Figure 8.20A Figure 8.20B

54 Infants with Down syndrome (per 1,000 births)
The chance of having a Down syndrome child Goes up with maternal age Age of mother 45 50 35 30 25 40 20 90 10 60 70 80 Infants with Down syndrome (per 1,000 births) Figure 8.20C

55 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

56 Nondisjunction in meiosis I Normal meiosis II Gametes n + 1 n 1 Number of chromosomes Nondisjunction in meiosis II Normal meiosis I n -1 n Number of chromosomes Figure 8.21B Figure 8.21A

57 Fertilization after nondisjunction in the mother
Sperm cell Egg cell n (normal) n + 1 Zygote 2n + 1 Figure 8.21C

58 CONNECTION 8.22 Abnormal numbers of sex chromosomes do not usually affect survival Nondisjunction can also produce gametes with extra or missing sex chromosomes Leading to varying degrees of malfunction in humans but not usually affecting survival Figure 8.22A Poor beard growth Breast Development Under-developed testes Figure 8.22B Characteristic facial features Web of skin Constriction of aorta Poor breast development Under developed ovaries

59 Human sex chromosome abnormalities

60 CONNECTION 8.23 Alterations of chromosome structure can cause birth defects and cancer Chromosome breakage can lead to rearrangements That can produce genetic disorders or, if the changes occur in somatic cells, cancer

61 Deletions, duplications, inversions, and translocations
Reciprocal translocation Nonhomologous chromosomes Deletion Duplication Inversion Homologous chromosomes Figure 8.23B “Philadelphia chromosome” Chromosome 9 Chromosome 22 Reciprocal translocation Activated cancer-causing gene Figure 8.23C Figure 8.23A

62 5,000

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