Cell Cycle Mitosis Meiosis GENETICS 1Dr MOHAMED FAKHRY

CELL DIVISION  All cells are derived from pre-existing cells  New cells are produced for growth and to replace damaged or old cells  Differs in prokaryotes (bacteria) and eukaryotes (fungi, plants, & animals) 2Dr MOHAMED FAKHRY

Keeping Cells Identical The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules 3Dr MOHAMED FAKHRY

DNA Replication DNA must be copied or replicated before cell division DNA must be copied or replicated before cell division Each new cell will then have an identical copy of the DNA Each new cell will then have an identical copy of the DNA Original DNA strand Two new, identical DNA strands 4Dr MOHAMED FAKHRY

Chromosomes 5

Prokaryotic Chromosome The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane 6Dr MOHAMED FAKHRY

Eukaryotic Chromosomes All eukaryotic cells store genetic information in chromosomes Most eukaryotes have between 10 and 50 chromosomes in their body cells Human body cells have 46 chromosomes or 23 identical pairs 7Dr MOHAMED FAKHRY

Eukaryotic Chromosomes Each chromosome is composed of a single, tightly coiled DNA molecule Chromosomes can’t be seen when cells aren’t dividing and are called chromatin 8Dr MOHAMED FAKHRY

Compacting DNA into Chromosomes DNA is tightly coiled around proteins called histones 9Dr MOHAMED FAKHRY

Chromosomes in Dividing Cells Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids 10

CELL REPRODUCTION 11Dr MOHAMED FAKHRY

Types of Cell Reproduction Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells Mitosis & binary fission= الانشطار الثنائي are examples of asexual reproduction Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote= البيضة الملقحة) that is NOT identical to the original cells. Meiosis is an example 12Dr MOHAMED FAKHRY

Cell Division in Prokaryotes 13Dr MOHAMED FAKHRY

Cell Division in Prokaryotes Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission Single chromosome makes a copy of itself Cell wall forms between the chromosomes dividing the cell Parent cell 2 identical daughter cells Chromosome doubles Cell splits 14

Eukaryotic Cell Division Used for growth and repair Produce two new cells identical to the original cell Cells are diploid (2n) Chromosomes during Metaphase of mitosis ProphaseMetaphase AnaphaseTelophase Cytokinesis 15

Cells divide at different rates. The rate of cell division varies with the need for those types of cells. 16

17  Not all cells are continually replicated.  Non-replicating cells are found in a stage of the cell cycle called G 0. These cells may be quiescent (dormant= خاملة او ساكنة) or senescent (aging = في مرحلة الشيخوخةor deteriorating).  Such cells generally enter the G 0 phase from G 1.  Cells may remain quiescent in G 0 for a period of time (when no more new cells are needed), only to re-enter G 1 phase and begin dividing again under specific conditions.  The quiescent cells may re-enter the cell cycle, senescent cells do not. These cells enter senescence= الشيخوخة to ensure= تضمن that damaged or defective DNA sequences is not passed on to daughter cells (offspring= الذرية). Some cells are unlikely to divide (G 0 )

Uncontrolled Mitosis If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors Oncogenes are special proteins increase the chance of the normal cell to develop into a tumor cell Oncogenes are special proteins that increase the chance of the normal cell to develop into a tumor cell Cancer cells 18

The Cell Cycle 19Dr MOHAMED FAKHRY

The cell cycle is a sequence of cell growth and division. The cell cycle is the period from the beginning of one division to the beginning of the next. The time it takes to complete one cell cycle is the generation time = وقت الجيل. 20Dr MOHAMED FAKHRY

Five Phases of the Cell Cycle G 1 - primary growth phase G 1 - primary growth phase S – synthesis; DNA replicated S – synthesis; DNA replicated G 2 - secondary growth phase G 2 - secondary growth phase collectively these 3 stages are called interphase M - mitosis M - mitosis C - cytokinesis C - cytokinesis 21Dr MOHAMED FAKHRY

Cell Cycle 22

Interphase - G 1 Stage 1 st growth stage after cell division 1 st growth stage after cell division Cells mature by making more cytoplasm & organelles Cells mature by making more cytoplasm & organelles Cell carries on its normal metabolic activities Cell carries on its normal metabolic activities 23Dr MOHAMED FAKHRY

Interphase – S Stage Synthesis stage Synthesis stage DNA is copied or replicated DNA is copied or replicated Two identical copies of DNA Original DNA 24Dr MOHAMED FAKHRY

Interphase – G 2 Stage 2 nd Growth Stage Occurs after DNA has been copied All cell structures needed for division are made (e.g. centrioles) Both organelles & proteins are synthesized 25Dr MOHAMED FAKHRY

22 Mitosis Division of the nucleus Also called karyokinesis Only occurs in eukaryotes Has four stages Doesn’t occur in some cells such as brain cells Dr MOHAMED FAKHRY

Early Prophase Chromatin in nucleus condenses to form visible chromosomes Mitotic spindle forms from fibers in cytoskeleton or centrioles (animal) Chromosomes Nucleolus Cytoplasm Nuclear Membrane 27

Late Prophase Nuclear membrane & nucleolus are broken down Nuclear membrane & nucleolus are broken down Chromosomes continue condensing & are clearly visible Chromosomes continue condensing & are clearly visible Spindle fibers called kinetochores attach to the centromere of each chromosome Spindle fibers called kinetochores attach to the centromere of each chromosome Spindle finishes forming between the poles of the cell Spindle finishes forming between the poles of the cell 28Dr MOHAMED FAKHRY

Spindle Fiber attached to Chromosome Kinetochore Fiber Chromosome 29

Review of Prophase What the cell looks like What’s happening 30

Metaphase Chromosomes, attached to the kinetochore fibers, move to the center of the cell Chromosomes are now lined up at the equator Pole of the Cell Equator of Cell= خط استواء الخلية اي وسطها Aster= شكل مثل النجم 31

Metaphase Chromosomes lined at the Equator Asters at the poles Spindle Fibers 32

Review of Metaphase What the cell looks like? What’s occurring ? 33

Anaphase Occurs rapidly Sister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers 34 Dr MOHAMED FAKHRY

Anaphase Sister Chromatids being separated 35

Anaphase Review What the cell looks like ? What’s occurring? 36

Telophase Sister chromatids at opposite poles Sister chromatids at opposite poles Spindle disassembles=يتفكك Spindle disassembles=يتفكك Nuclear envelope forms around each set of sister chromatids Nuclear envelope forms around each set of sister chromatids Nucleolus reappears Nucleolus reappears CYTOKINESIS occurs CYTOKINESIS occurs Chromosomes reappear as chromatin Chromosomes reappear as chromatin 37Dr MOHAMED FAKHRY

Comparison of Anaphase & Telophase 38

Cytokinesis Means division of the cytoplasm Division of cell into two, identical halves called daughter cells In plant cells, cell plate (cell wall) forms at the equator to divide cell In animal cells, cleavage furrow= اخدود او شق forms to split cell 39Dr MOHAMED FAKHRY

Cytokinesis Cleavage furrow in animal cell Cell plate in plant cell 40

Daughter Cells of Mitosis Have the same number of chromosomes as each other and as the parent cell from which they were formed Identical (in genetic materials) to each other, but smaller than parent cell Must grow in size to become mature cells (G 1 of Interphase) 41Dr MOHAMED FAKHRY

Identical Daughter Cells Chromosome number the same, but cells smaller than parent cell What is the 2n or diploid number? 2 42Dr MOHAMED FAKHRY

Review of Mitosis 43

Review of Mitosis 44

Meiosis Formation of Gametes (Eggs & Sperm) 45Dr MOHAMED FAKHRY

Facts About Meiosis It is preceded by interphase which includes chromosome replication It has two meiotic divisions: Meiosis I and Meiosis II It is Called reduction- division= انقسام إختزالي The original cell is diploid (2n) Four daughter cells produced that are monoploid (1n) 46Dr MOHAMED FAKHRY

Facts About Meiosis Daughter cells contain half the number of chromosomes as the original cell Produces gametes = الامشاج (eggs & sperm) Occurs in the testes in male (Spermatogenesis) Occurs in the ovaries in females (Oogenesis) 47Dr MOHAMED FAKHRY

Start with 46 double stranded chromosomes (2n) After 1 division - 23 double stranded chromosomes (n) After 1 division - 23 double stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n) After 2nd division - 23 single stranded chromosomes (n) Occurs in our germ cells= خلايا الاصل أو خلايا البذرة that produce gametes More Meiosis Facts 48Dr MOHAMED FAKHRY

49 What is the importance of Meiosis? It is the fundamental basis of sexual reproduction Two haploid= monoploid (1n) gametes are brought together through fertilization= الخصاب و التخصيب to form a diploid (2n) zygote= البويضة الملقحة او المخصبة

50 Fertilization – “Putting it all together” 1n =3 2n = 6

51 Replication of Chromosomes Replication is the process of duplicating a chromosome Occurs prior to division Replicated copies are called sister chromatids Held together at centromere Occurs in Interphase

52 A Replicated Chromosome Homologs = Homologs = (same genes, (same genes, different alleles) Sister Chromatids (same genes, same alleles) Gene X Homologs= متماثل -متجانس separate in meiosis I and therefore different alleles separate.

53 Meiosis Forms Haploid Gametes Meiosis must reduce the chromosome number by half Meiosis must reduce the chromosome number by half Fertilization then restores the 2n number Fertilization then restores the 2n number from momfrom dadchild meiosis reduces genetic content too much! The right number!

54 Meiosis: Two Part Cell DivisionHomologsseparate Sister chromatids separate Diploid Meiosis I Meiosis II Diploid Haploid

55 Meiosis I: Reduction Division Nucleus Spindlefibers Nuclearenvelope Early Prophase I (Chromosome number doubled) Late Prophase I Metaphase I Anaphase I Telophase I (diploid) Dr MOHAMED FAKHRY

56 Prophase I Early prophase Homologs pair. Homologs pair. Crossing over occurs Crossing over occurs. Late prophase Chromosomes condense. Chromosomes condense. Spindle forms. Spindle forms. Nuclear envelope fragments. Nuclear envelope fragments. Dr MOHAMED FAKHRY

57 Tetrads Form in Prophase I Homologous chromosomes (each with sister chromatids) Homologous chromosomes (each with sister chromatids) Join to form a TETRAD Called Synapsis

58 Crossing-Over Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes are exchanged Produces Genetic recombination in the offspring الزرية او = النسل

59 Metaphase I Homologous pairs= متماثل او متجانس of chromosomes align along the equator of the cell Dr MOHAMED FAKHRY

60 Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres Sister chromatids remain attached at their centromeres. Dr MOHAMED FAKHRY

61 Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. Dr MOHAMED FAKHRY

62 Meiosis II Only one homolog of each is present in the cell Only one homolog of each chromosome is present in the cell Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene Sister chromatids carry identical genetic information Gene X Dr MOHAMED FAKHRY

63 Meiosis II: Reducing Chromosome Number Prophase II Metaphase II Anaphase II Telophase II4 Identical haploid cells Dr MOHAMED FAKHRY

64 Prophase II Nuclear envelope fragments. Spindle forms. Dr MOHAMED FAKHRY

65 Metaphase II Chromosomes align= بمحازاة along equator of cell. Dr MOHAMED FAKHRY

66 Anaphase II Sister chromatids separate and move to opposite poles Sister chromatids separate and move to opposite poles. Equator Pole Dr MOHAMED FAKHRY

67 Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. Dr MOHAMED FAKHRY

68 Results of Meiosis  Formation of gametes (egg &sperm)  Four haploid cells with one copy of each chromosome  One allele of each gene  Different combinations of alleles for different genes along the chromosome Dr MOHAMED FAKHRY

69 MitosisMeiosis Number of divisions 1 2 Number of daughter cells 24 Genetically identical? YesNo Chromosome # Same as parent Half of parent Where ? Somatic cells Germ cells When? Throughout life At sexual maturity Role Growth and repair Sexual reproduction Comparison of Divisions