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Mitosis & Meiosis
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Cell Division like begets like (more or less)
reproduction occurs at the cellular level have to give genetic material to new cell asexual sexual haploid = one set of DNA (1n) diploid = 2 sets of DNA (2n)
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Asexual production of genetically identical offspring by a single parent 1 parent cell (2n) → 2 daughter cells (2n) DNA is identical aka: cloning whole organisms cells within an organism (growth & repair)
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Sexual production of genetically unique offspring
genetic contribution from 2 different parents need to reduce the amount of DNA by half creates gametes (egg & sperm) gamete + gamete → new organism (1n) (1n) → (2n)
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Prokaryotes: Binary Fission
single chromosome circular small and uncomplicated stimulus to divide: lots of food get too large: own waste = death need ATP to: make new set of DNA make new cell ‘stuff’
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Figure 10.2 Cell Division in a Prokaryote
Many prokaryotes, including many types of bacteria, propagate themselves asexually through a type of cell division known as binary fission.
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Prokaryotic chromosomes
Figure 8.2B Prokaryotic chromosomes Figure 8.2B An electron micrograph of a dividing bacterium 7
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Eukaryotes: Mitosis larger, more complex cells
large numbers of chromosomes chromosomes in pairs: 1 from mom & 1 from dad DNA is unwound most of the time: chromatin duplicate in this form = 4 sets of DNA time to divide, need to organize: wind up into chromatids
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Eukaryotes: Mitosis cells spend most of their time in Interphase
G1 phase: doing it’s thing but able to start dividing G0 phase: doing it’s thing but can’t divide S phase: synthesis (duplicate DNA & centrosome) G2 phase: really getting ready to divide
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Figure 10.5 The Cell Cycle Consists of Two Major Stages: Interphase and Cell Division
The cell prepares itself for division by increasing in size and producing proteins needed for division during G1 and G2 phases, and by replicating its DNA during S phase. Mitotic cell division consists of mitosis and cytokinesis, which result in two daughter cells that are genetically identical to the parent cell.
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Figure 10.7 The Packing of DNA into a Chromosome
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Figure 10.8 Each Replicated Chromosome Consists of Two Identical Sister Chromatids
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Eukaryotes: Mitosis Prophase
chromatin condenses into sister chromatids mitotic spindle forms microtubules attach to the centrosomes & centromere nuclear membrane breaks down mitotic spindle starts pushing chromatids toward middle of ce
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Figure 10.10 (Part 1) Mitosis and Cytokinesis Are the Two Main Stages of Mitotic Cell Division
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Eukaryotes: Mitosis Metaphase Anaphase
all the centromeres are lined up at equatorial plane Anaphase checkpoint ATP used to push and pull centromeres toward poles poles pushed away from each other too fastest phase
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Figure 10.10 (Part 2) Mitosis and Cytokinesis Are the Two Main Stages of Mitotic Cell Division
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Eukaryotes: Mitosis Telophase Cytokinesis ‘reverse’ of prophase
chromatids unwind spindle breaks down nucleus reforms Cytokinesis contractile ring of actin & myosin forms (hoodie) plants form a cell plate → cell wall make more ‘stuff’
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Figure 10.10 (Part 2) Mitosis and Cytokinesis Are the Two Main Stages of Mitotic Cell Division
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Figure 10.11 Cytokinesis in an Animal Cell
This fluorescence image shows cytokinesis in a sea urchin zygote that is dividing into two cells. Microtubules are orange, actin filaments blue.
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Cleavage furrow Daughter cells
Figure 8.6A Cytokinesis Cleavage furrow Contracting ring of microfilaments Daughter cells Figure 8.6A Cleavage of an animal cell Cleavage furrow 22
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Figure 10.12 Cell Plate Formation Is a Distinctive Feature of Cytokinesis in Plant Cells
(a) A microscopic view of mitosis and cytokinesis in lily pollen. The cell plate appears as a pale line in the center of the cell, in the last photograph in the series (telophase). (b) A diagrammatic view of the main events in mitosis and cytokinesis in a plant cell. Plant cells lack prominent centrosomes, but have structures that perform the same function.
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Mitosis: Summary start with 1 2n parent
end up with 2 2n daughter cells DNA in daughter cells is IDENTICAL to each other to parent cell
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Figure 10.3 Cell Division in a Eukaryote
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Meiosis start with 1 2n parent cell produce 4 1n gametes DNA is UNIQUE
each gamete is different than the others each gamete is different than the parent
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Meiosis somatic cells (body cells) have 2 sets of chromosomes
called homologous pairs code for same things, (like eye color) but may have different information (blue or brown) 22 pairs of austosomes 1 pair of sex chromosome (XX in female; XY male)
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Meiosis gametes (1n) gamete + gamete → zygote (fertilization)
have 1 set of chromosomes meant to pair up with another gamete (1n) to create a 2n organism gamete + gamete → zygote (fertilization) (1n) (1n) (2n) gametes created through process of MEIOSIS
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Meiosis DNA is copied ONCE cells divide TWICE
cross-over: homologous chromosomes swap material = increased genetic diversity
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Mom Dad
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Mom Dad
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Figure 10.14 In Meiosis, Each Daughter Cell Receives Half the Chromosome Set
The maternal and paternal homologues are paired during prophase I through metaphase I, and separated from each other during anaphase. Meiosis II is similar to mitosis in that the sister chromatids that compose each replicated chromosome are pulled apart. For simplicity and clarity, not all the steps described in the text are illustrated here.
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Sister chromatids A pair of homologous chromosomes in a diploid
Figure 8.12B INTERPHASE MEIOSIS I MEIOSIS II Sister chromatids 1 2 3 A pair of homologous chromosomes in a diploid parent cell A pair of duplicated homologous chromosomes Figure 8.12B How meiosis halves chromosome number 34
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Pair of homologous chromosomes One duplicated chromosome
Figure 8.11 Pair of homologous chromosomes Locus Centromere Sister chromatids Figure 8.11 A pair of homologous chromosomes One duplicated chromosome 35
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Meiosis Interphase: chromosomes duplicated centrosomes duplicated
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Figure 10.14 In Meiosis, Each Daughter Cell Receives Half the Chromosome Set
The maternal and paternal homologues are paired during prophase I through metaphase I, and separated from each other during anaphase. Meiosis II is similar to mitosis in that the sister chromatids that compose each replicated chromosome are pulled apart. For simplicity and clarity, not all the steps described in the text are illustrated here.
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Meiosis Prophase I: chromatin coils up
synapsis: 2 sister chromatids come together (tetrad) cross over occurs can take months centrosomes go to poles spindle foms nuclear envelope breaks down
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Figure 10.14 In Meiosis, Each Daughter Cell Receives Half the Chromosome Set
The maternal and paternal homologues are paired during prophase I through metaphase I, and separated from each other during anaphase. Meiosis II is similar to mitosis in that the sister chromatids that compose each replicated chromosome are pulled apart. For simplicity and clarity, not all the steps described in the text are illustrated here.
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Meiosis Metaphase I: tetrads are aligned across from each other at equator sister chromatids across from each other not all centromeres along equator
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Figure 10.14 In Meiosis, Each Daughter Cell Receives Half the Chromosome Set
The maternal and paternal homologues are paired during prophase I through metaphase I, and separated from each other during anaphase. Meiosis II is similar to mitosis in that the sister chromatids that compose each replicated chromosome are pulled apart. For simplicity and clarity, not all the steps described in the text are illustrated here.
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Meiosis Anaphase I: sister chromatids pulled away from each other
uses ATP to push/pull chromatids toward poles uses ATP to push poles away from each other
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Figure 10.14 In Meiosis, Each Daughter Cell Receives Half the Chromosome Set
The maternal and paternal homologues are paired during prophase I through metaphase I, and separated from each other during anaphase. Meiosis II is similar to mitosis in that the sister chromatids that compose each replicated chromosome are pulled apart. For simplicity and clarity, not all the steps described in the text are illustrated here.
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Meiosis Telophase I and Cytokinesis: nuclear membrane reforms
chromatids uncoil into chromatin some species skip this short interphase (rest)
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Figure 10.14 In Meiosis, Each Daughter Cell Receives Half the Chromosome Set
The maternal and paternal homologues are paired during prophase I through metaphase I, and separated from each other during anaphase. Meiosis II is similar to mitosis in that the sister chromatids that compose each replicated chromosome are pulled apart. For simplicity and clarity, not all the steps described in the text are illustrated here.
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Meiosis Prophase II: Metaphase II: centosomes duplicate spindle forms
chromosomes moved toward equator Metaphase II: centromeres aligned on equator
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Figure 10.14 In Meiosis, Each Daughter Cell Receives Half the Chromosome Set
The maternal and paternal homologues are paired during prophase I through metaphase I, and separated from each other during anaphase. Meiosis II is similar to mitosis in that the sister chromatids that compose each replicated chromosome are pulled apart. For simplicity and clarity, not all the steps described in the text are illustrated here.
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Meiosis Anaphase II: Telophase II & Cytokinesis:
centromeres of sister chromatids pulled apart ATP used to push/pull chromatids toward poles ATP used to push poles away from each other Telophase II & Cytokinesis: nuclei reform DNA uncoils
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Figure 10.14 In Meiosis, Each Daughter Cell Receives Half the Chromosome Set
The maternal and paternal homologues are paired during prophase I through metaphase I, and separated from each other during anaphase. Meiosis II is similar to mitosis in that the sister chromatids that compose each replicated chromosome are pulled apart. For simplicity and clarity, not all the steps described in the text are illustrated here.
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(before chromosome duplication)
Figure 8.14 MITOSIS MEIOSIS I Parent cell (before chromosome duplication) Prophase Site of crossing over Prophase I Duplicated chromosome (two sister chromatids) Tetrad formed by synapsis of homologous chromosomes Chromosome duplication Chromosome duplication 2n 4 Metaphase Metaphase I Chromosomes align at the metaphase plate Tetrads (homologous pairs) align at the metaphase plate Anaphase Telophase Anaphase I Telophase I Homologous chromosomes separate during anaphase I; sister chromatids remain together Figure 8.14 Comparison of mitosis and meiosis Sister chromatids separate during anaphase Daughter cells of meiosis I Haploid n 2 MEIOSIS II 2n 2n No further chromosomal duplication; sister chromatids separate during anaphase II Daughter cells of mitosis n n n n Daughter cells of meiosis II 51
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Figure 10.15 Crossing-over Produces Recombinant Chromosomes
Crossing-over is the physical exchange of corresponding segments between the non–sister chromatids in a pair of homologous chromosomes that are aligned parallel to each other during prophase I. For clarity, only one maternal and one paternal chromatid are depicted here as exchanging segments. In human cells undergoing meiosis, most tetrads have one to three crossover sites, with longer chromosomes more likely to have multiple crossovers. A crossover site can be located at any point along the length of the paired homologues (tetrad), not just at the tips of the chromatids. The letters (A/a and B/b) represent alternative alleles of two genes, A and B. Note that the parental combinations of these alleles have been shuffled in the recombinant chromosomes.
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Figure The Random Assortment of Homologous Chromosomes Generates Chromosomal Diversity among Gametes
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Figure 8.19A_1 Figure 8.19A_1 A karyotype showing trisomy 21 Trisomy 21 54
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MEIOSIS I Nondisjunction Figure 8.20A_s1
Figure 8.20A_s1 Nondisjunction in meiosis I (step 1) 55
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MEIOSIS I Nondisjunction MEIOSIS II Normal meiosis II Figure 8.20A_s2
Figure 8.20A_s2 Nondisjunction in meiosis I (step 2) 56
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MEIOSIS I Nondisjunction MEIOSIS II Normal meiosis II Gametes
Figure 8.20A_s3 MEIOSIS I Nondisjunction MEIOSIS II Normal meiosis II Figure 8.20A_s3 Nondisjunction in meiosis I (step 3) Gametes Number of chromosomes n 1 n 1 n 1 n 1 Abnormal gametes 57
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MEIOSIS I Normal meiosis I Figure 8.20B_s1
Figure 8.20B_s1 Nondisjunction in meiosis II (step 1) 58
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MEIOSIS I Normal meiosis I MEIOSIS II Nondisjunction Figure 8.20B_s2
Figure 8.20B_s2 Nondisjunction in meiosis II (step 2) 59
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MEIOSIS I Normal meiosis I MEIOSIS II Nondisjunction n 1 n 1 n n
Figure 8.20B_s3 MEIOSIS I Normal meiosis I MEIOSIS II Nondisjunction Figure 8.20B_s3 Nondisjunction in meiosis II (step 3) n 1 n 1 n n Abnormal gametes Normal gametes 60
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Figure 13.14 Chromosome Rearrangements Can Cause Serious Genetic Disorders
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Figure 13.14a Chromosome Rearrangements Can Cause Serious Genetic Disorders
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Figure 13.14b Chromosome Rearrangements Can Cause Serious Genetic Disorders
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Figure 13.14c Chromosome Rearrangements Can Cause Serious Genetic Disorders
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Figure 13.14d Chromosome Rearrangements Can Cause Serious Genetic Disorders
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