Cellular Reproduction: A Comprehensive Guide to Chromosomes, Division, and Genetic Inheritance

1. CellularReproduction Chapter 8

2. WHAT CELL REPRODUCTION ACCOMPLISHES • Reproduction • Is the birth of new organisms • Occurs much more often at the cellular level Cell division plays a role in • The replacement of lost or damaged cells • Cell reproduction and growth

3. The Reproduction of Organisms • Asexual reproduction: the parent produces a clone of itself • Many single-celled organisms reproduce by simple cell division or mitosis Amoeba

4. Asexual reproduction (Hydra) • Some multicellular organisms can divide into pieces that then grow into new individuals Hydra

5. Other organisms make similar copies of themselves in a more complex process, sexual reproduction

6. Sexual reproduction • Requires fertilization of an egg by a sperm • Production of egg and sperm (gametes) is called by a special type of cell division called meiosis

7. 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 (mitosis) • It also ensures the continuity of life from one generation to the next (meiosis)

8. A genome • Is the complete set of an organism’s genes • Is located in the cytoplasm in prokaryotes • Is located mainly on chromosomes (DNA + protein) in the cell’s nucleus in eukaryotes

9. Eukaryotic Chromosomes Chromosomes • Are made of chromatin, a combination of DNA and protein molecules • Chromatin is not visible in a cell until cell division

10. DNA double helix Histones “Beads on a string” • The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding Nucleosome Tight helical fiber Supercoil Centromere Sister chromatids

11. Before a cell divides, each chromosome duplicates itself resulting in two copies called sister chromatids • Sister chromatids remain connected at the centromere until cell division

12. Chromosome duplication • When the cell divides, the sister chromatids separate from each other Sister chromatids Centromere Chromosome distribution to daughter cells

13. Structure of a chromosome

14. Normal male karyotype

15. Chromosomes • Chromosomes occur as homologous pairs in a diploid organism Each homologous pair: • Is identical in length and position of centromere • Similar banding pattern • Carries genes that control the same inherited characteristics at corresponding loci ( specific location of a gene or DNA sequence on a chromosome) • However, each homologue may carry a different version of the gene (allele)

16. Homologous Chromosomes • Different organisms of the same species have the same number and types of chromosomes Chromosomes Centromere • Human cells have 23 pairs of homologous chromosomes (46) Sister chromatids

17. What is Down Syndrome? Down syndrome (DS), also called Trisomy 21, is a condition in which extra genetic material causes delays in the way a child develops, both mentally and physically. It affects about 1 in every 800 babies Chromosome 21 has 3 chromosomes instead of 2 . http://kidshealth.org/parent/medical/genetic/down_syndrome.html#

18. What Causes DS? • Normally, at the time of conception a baby inherits genetic information from its parents: • 46 chromosomes: 23 from the mother and 23 from the father. • In most cases of Down syndrome, a child gets an extra chromosome 21 — for a total of 47 chromosomes instead of 46. • It's this extra genetic material that causes the physical features and developmental delays associated with DS. • http://kidshealth.org/parent/medical/genetic/down_syndrome.html#

19. Chromosome numbers in different species • Homo sapiens (human) 2n = 46 • Drosophila melanogaster (fruit fly) 2n = 8 • Arabidopsis thaliana (plant in the mustard family) 2n = 10 • Canis familiaris (domestic dog) 2n = 78 • Gallus gallus (chicken) 2n = 78 • Zea mays (corn or maize) 2n = 20 • Myrmecia pilosula (an ant) 2n = 2

20. Passing On the Genes from Cell to Cell • Before a parent cell divides, it duplicates its chromosomes The two resulting “daughter” cells are genetically identical

21. 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

22. Prokaryoticchromosome Plasmamembrane Cell wall Binary fission of a prokaryotic cell Duplication of chromosomeand separation of copies Continued growth of the cell and movement of copies Division intotwo cells

23. Eukaryotic cells that divide undergo an orderly sequence of events called the cell cycle The l Cycle S phase (DNA synthesis; chromosome duplication) • The cell cycle consists of two distinct phases: S phase Interphase (90% of time) G1 G2 • Interphase • Mitotic phase Mitotic phase (M) (10% of time) Mitosis Cytokinesis

24. Cell division is a continuum of dynamic changes • Eukaryotic cell division consists of two stages: • Mitosis • Cytokinesis In mitosis, the duplicated chromosomes are distributed into two daughter nuclei

25. After the chromosomes coil up, a mitotic spindle moves them to the middle of the cell - The sister chromatids then separate and move to opposite poles of the cell • -The process of cytokinesis divides the cell into two genetically identical cells

26. Interphase Mitosis and Cytokinesis • Mitosis is: • the division of the chromosomes • preceded by interphase Centrosomes (with centriole pairs) Chromatin Nucleolus Nuclear envelope Plasma membrane

27. Prophase • Metaphase • Anaphase • Telophase • Mitosis consists of four distinct phases

28. Prophase Metaphase Centrosome Fragments of nuclear envelope Early mitotic spindle Centromere Chromosome, consisting of two sister chromatids Spindle microtubules Spindle

29. Anaphase Telophase & Cytokinesis 3. Anaphase 4. Telophase Nucleolus forming Cleavage furrow Daughter chromosomes Nuclear envelope forming

30. Cytokinesis • Typically occurs during telophase • Is the division of the cytoplasm

31. Cleavage furrow • Cytokinesis is different in plant and animal cells Cleavage furrow Contracting ring of microfilaments Animal cell cytokinesis Daughter cells (a) Animal cell cytokinesis

32. Cell plate forming Wall of parent cell Daughter nucleus Plant cell cytokinesis Vesicles containing cell wall material New cell wall Cell plate Cell wall (b) Plant cell cytokinesis Daughter cells

33. Mitosis

34. Review of the functions ofmitosis: Growth-,asexual reproduction • When the cell cycle operates normally, mitotic cell division functions in: • Growth (seen here in an onion root)

35. Deadcells Skin cell placement Epidermis, the outer layer of the skin Dividingcells Dermis

36. Sea star regenerating a lost arm Asexual reproduction (hydra)

37. MEIOSIS, THE BASIS OF SEXUAL REPRODUCTION • Sexual reproduction depends on Meiosis Fertilization • A somatic cell • Is a typical body cell • Has 46 chromosomes in a human

38. Humans have: • Autosomes are present in males and females • Sex chromosomes – determines gender, varies in males (XY) and females (XX) • Two different sex chromosomes, X and Y • 22 pairs of matching chromosomes, called autosomes

39. Chromosomes Chromosomes • Occur as homologous pairs in a diploid organism • Each homologous pair - is identical in length and position of centromere - Similar banding pattern - Carry genes that control the same inherited characteristics at corresponding loci - However, each homologue may carry a different version of the gene (allele)

40. Homologous Chromosomes • Different organisms of the same species have the same number and types of chromosomes Chromosomes Centromere - Human cells have 23 pairs of homologous chromosomes Sister chromatids

41. Pair of homologous chromosomes Centromere • A karyotype is an orderly arrangement of chromosomes Sister chromatids Homologous chromosomes are matching pairs of chromosomes

42. Gametes and the Life Cycle of a Sexual Organism (Human) Haploid gametes (n = 23) n Egg cell n Sperm cell Meiosis Fertilization Diploid zygote (2n = 46) Male and female Adults (2n = 46) 2n Mitosis and development

43. Their cells contain two sets of chromosomes • Their gametes are haploid (n), having only one set of chromosomes • Humans are diploid organisms (2n) • Fertilization • Is the fusion of sperm (n) and egg (n) • Creates a zygote (2n), or fertilized egg

44. Meiosis reduces the chromosome number from diploid to haploid • Meiosis, like mitosis, is preceded by chromosome duplication • However, in meiosis the cell divides twice to form four daughter cells

45. Sexual life cycles involve an alternation of diploid and haploid stages 2 Homologous chromosomes separate 1 Chromosomes duplicate 3 Sister chromatids separate Homologous pair of chromosomes in diploid parent cell Homologous pair of duplicated chromosomes Sister chromatids Meiosis I Meiosis II Interphase before meiosis

46. The Process of Meiosis Interphase Centrosomes (with centriole pairs) • In meiosis • Haploid gametes are produced in diploid organisms • Two consecutive divisions occur, meiosis I and meiosis II, preceded by interphase • Crossing over occurs Nuclear envelope Chromatin Chromosomes duplicate

47. In the first division, meiosis I, homologous chromosomes are paired • While they are paired, they cross over and exchange genetic information • The homologous pairs are then separated, and two daughter cells are produced

48. Meiosis I Meiosis I: Homologous chromosomes separate Telophase I and Cytokinesis Prophase I Metaphase I Anaphase I Sister chromatids remain attached Sites of crossing over Microtubules attached to chromosomes Cleavage furrow • Meiosis I Spindle Sister chromatids Centromere Tetrad Homologous chromosomes pair and exchange segments Two haploid cells form: chromosomes are still double Tetrads line up Pairs of homologous chromosomes split up

49. Meiosis II: Sister chromatids separate Telophase II and Cytokinesis Prophase II Metaphase II Anaphase II • Meiosis II Sister chromatids separate Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes

50. MITOSIS MEIOSIS PARENT CELL(before chromosome replication) MEIOSIS I Site ofcrossing over PROPHASE PROPHASE I Tetrad formedby synapsis of homologous chromosomes Duplicatedchromosome(two sister chromatids) Chromosomereplication Chromosomereplication 2n = 4 METAPHASE METAPHASE I Chromosomes align at the metaphase plate Tetradsalign at themetaphase plate ANAPHASETELOPHASE Homologouschromosomesseparateduringanaphase I;sisterchromatids remain together ANAPHASE I TELOPHASE I Sister chromatidsseparate duringanaphase Haploidn = 2 MEIOSIS II 2n 2n Daughtercells of meiosis I No further chromosomal replication; sister chromatids separate during anaphase II Daughter cellsof mitosis n n n n Daughter cells of meiosis II