A Darwinian View of Life I. Darwin’s Contributions II. Mendel's Contributions III. The Cellular Context

A. Cell Structure/Function Review

III. The Cellular Context A. Cell Structure/Function Review 1. Membrane:

III. The Cellular Context A. Cell Structure/Function Review 1. Membrane: regulates what gets in/out, largely through protein channels.

III. The Cellular Context A. Cell Structure/Function Review 1. Membrane: regulates what gets in/out, largely through protein channels. 2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria). ATP

III. The Cellular Context A. Cell Structure/Function Review 1. Membrane: regulates what gets in/out, largely through protein channels. 2. Energy Harvest: ATP

III. The Cellular Context A. Cell Structure/Function Review 1. Membrane: regulates what gets in/out, largely through protein channels. 2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria). 3. Energy used to catalyze reactions: ATP RNA PROTEIN ribosome Endoplasmic Reticulum

III. The Cellular Context A. Cell Structure/Function Review 1. Membrane: regulates what gets in/out, largely through protein channels. 2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria). 3. Energy used to catalyze reactions… often building proteins by protein synthesis (reading DNA and making RNA and protein) ATP RNA PROTEIN ribosome Endoplasmic Reticulum

III. The Cellular Context A. Cell Structure/Function Review 1. Membrane: regulates what gets in/out, largely through protein channels. 2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria). 3. Energy used to catalyze reactions… often building proteins by protein synthesis (reading DNA and making RNA and protein) 4. Energy used for cell division. ATP RNA PROTEIN ribosome Endoplasmic Reticulum

III. The Cellular Context A. Cell Structure/Function Review 1. Membrane: regulates what gets in/out, largely through protein channels. 2. Energy Harvest by protein photosystems and protein enzymes in chloroplasts AND/OR cellular respiration (protein enzymes in cytoplasm and mitochondria). 3. Energy used to catalyze reactions… often building proteins by protein synthesis (reading DNA and making RNA and protein) 4. Energy used for cell division ATP RNA PROTEIN ribosome Endoplasmic Reticulum DNA (genes) are recipes for proteins, and proteins are critical to cell metabolism, growth, reproduction, regulation of gene action, and response to the environment.

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin, either: unreplicated (one DNA double-helix) OR Replicated (two double-helices)

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin, either: unreplicated (one DNA double-helix) OR Replicated (two double-helices) A single DNA double-helix, bound with the associated proteins (pink), is called a ‘chromatid’. An unreplicated chromosome has one chromatid. A replicated chromosome has two chromatids that are IDENTICAL COPIES

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there?

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? - in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n) A b C d

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? - in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n) - we then make reference to the NUMBER of chromosomes present: “1n = 2” A b C d

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? - in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n) - we then make reference to the NUMBER of chromosomes present: “1n = 2” - In eukaryotes, gametes and spores are haploid (typically) A b C d

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? - in simplistic terms, if a cell has ‘one gene for every trait’ = haploid (1n) - we then make reference to the NUMBER of chromosomes present: “1n = 2” - A haploid set is also called the ‘genome’ – representing all the genetic information needed to encode an organism of that species. SpeciesHaploid Number Domestic cat19 Human23 Chicken39 Dog39 Water Fly80

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? - In eukaryotes, gametes and spores are haploid (typically) - bacteria and archaeans have one circular chromosome and so are haploid organisms that do NOT reproduce by gamete production/fusion. A b C d

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? A b C d a B C D - when haploid gametes fuse during fertilization, a zygote with two genes for every trait is formed. This cell is DIPLOID, 2n = 4.

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? A b C d a B C D - when haploid gametes fuse during fertilization, a zygote with two genes for every trait is formed. This cell is DIPLOID, 2n = 4. - NOTE that the two chromosomes of the same color are not IDENTICAL. They govern the same traits, but the genes that they have for these traits can be different alleles (forms of a gene) that influence that trait in different ways. Chromosomes that govern the same traits are called HOMOLOGOUS

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? - Many organisms (indeed, maybe MOST flowering plant species) are POLYPLOID, and have several sets of chromosomes… like this Tetraploid (4n = 8). A b C d a B C D A b C d A b C d

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? - Many organisms (indeed, maybe MOST flowering plant species) are POLYPLOID, and have several sets of chromosomes… like this Tetraploid (4n = 8). A b C d a B C D - when it makes gametes/spores (with ½ the genetic info as the parent cell), it will make diploid gametes… so not ALL gametes are haploid. A b C d A b C d

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology 1. chromatin: indistinguishable, diffuse chromosomes 2. chromosome: condensed strand of chromatin 3. “Ploidy” refers to the “information content” in the cell… how many ‘sets’ of chromosomes are there? 4. Chromosomes are identified and classified by their length, banding pattern, and position of the centromere.

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle - Interphase: Poorly named – the cell is most active metabolically, growing, building proteins, replicating its DNA, and preparing for division. Chromosomes are diffuse – “chromatin” – DNA recipes are being ‘read’ and proteins are synthesized, or DNA is being replicated. Three substages: G1, S, G2

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle - Interphase: G1: the cell is most active metabolically, growing and building proteins appropriate for that cell. Cell may be “arrested” in this stage and not divide again (neurons, muscle). If so, it is more appropriately said that the cell has entered the G 0 stage. The cell also ‘proof-reads’ and repairs DNA during this stage.

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle - Interphase: G1: the cell is most active metabolically, growing and building proteins appropriate for that cell. Cell may be “arrested” in this stage and not divide again (neurons, muscle). If so, it is more appropriately said that the cell has entered the G 0 stage. The cell also ‘proof-reads’ and repairs DNA during this stage. S: (“synthesis”) DNA replication occurs; each chromosome transitions from its unreplicated (one DNA double-helix) to its replicated (two DNA double-helices) state.

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle - Interphase: G1: the cell is most active metabolically, growing and building proteins appropriate for that cell. Cell may be “arrested” in this stage and not divide again (neurons, muscle). If so, it is more appropriately said that the cell has entered the G 0 stage. The cell also ‘proof-reads’ and repairs DNA during this stage. S: (“synthesis”) DNA replication occurs; each chromosome transitions from its unreplicated (one DNA double-helix) to its replicated (two DNA double-helices) state. G2: Preparatory for division; in animals, centrioles are made during this period. DNA is repaired (and errors made during replication) can be corrected before division.

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle - Interphase: - “Checkpoints”: The transition from G1 is critical; when a cell crosses this ‘checkpoint’ late in G1, it is committed to dividing. Likewise, the transition from G2 is critical, because the DNA will be passed to daughter cells in its present state. If these checks are poorly regulated, cells can divide prematurely, before DNA proof- reading is complete. This increases the number of mutations passed to daughter cells, leading to further problems with cell division regulation. Ultimately, cells may keep dividing with little or no regulation, as a tumor.

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle D. Cell Division: Mitosis

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle D. Cell Division: Mitosis

LE 12-9a Cleavage furrow 100 µm Contractile ring of microfilaments Daughter cells Cleavage of an animal cell (SEM)

LE 12-9b 1 µm Daughter cells Cell plate formation in a plant cell (TEM) New cell wall Cell plate Wall of parent cell Vesicles forming cell plate

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle D. Cell Division: Mitosis E. Meiosis 1. Overview 2n 1n REDUCTIONDIVISION

E. Meiosis 1. Overview 2. Meiosis I (Reduction) There are four replicated chromosomes in the initial cell. Each chromosomes pairs with its homolog (that influences the same suite of traits), and pairs align on the metaphase plate. Pairs are separated in Anaphase I, and two cells, each with only two chromosomes, are produced. REDUCTION

E. Meiosis 1. Overview 2. Meiosis I (Reduction) There are four replicated chromosomes in the initial cell. Each chromosomes pairs with its homolog (that influences the same suite of traits), and pairs align on the metaphase plate. Pairs are separated in Anaphase I, and two cells, each with only two chromosomes, are produced. REDUCTION PROPHASE I: - leptonema: condensation begins, and “homolog search” occurs - zygonema: condensation continues and homologs align and begin to interact - pachynema: condensation is completed, and the homologs synapse – chemically bound along length, and exchange of DNA between homologs occurs (crossing over) - diplonema: homologs begin to separate, and points of contact (chiasma) are thought to indicate where crossing over occurred. - diakinesis: separation of homologs and breakdown of nuclear envelope; attachment of spindle fibers

E. Meiosis 1. Overview 2. Meiosis I (Reduction) There are four replicated chromosomes in the initial cell. Each chromosomes pairs with its homolog (that influences the same suite of traits), and pairs align on the metaphase plate. Pairs are separated in Anaphase I, and two cells, each with only two chromosomes, are produced. REDUCTION

E. Meiosis 1. Overview 2. Meiosis I (Reduction) 3. Transition 4. Meiosis II (Division) Each cell with two chromosomes divides; sister chromatids are separated. There is no change in ploidy in this cycle; haploid cells divide to produce haploid cells. DIVISION

5. Modifications in anisogamous and oogamous species

III. The Cellular Context A. Cell Structure/Function Review B. Chromosomal Terminology C. The Cell Cycle D. Cell Division: Mitosis E. Meiosis F. Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory of inheritance

F. Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory Sutton and Boveri (independently) saw homologous chromosomes separating (segregating) during meiosis. If they carried genes, this would explain Mendel’s first law. Theodor Boveri Walter Sutton Aa

F. Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory And if the way one pair of homologs separated had no effect on how others separated, then the movement of homologs would explain Mendel’s second law, also! They proposed that chromosomes carry the heredity information. Theodor Boveri Walter Sutton Aa Aa bBBb ABabAbaB OR

F. Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma Independent Assortment produces an amazing amount of genetic variation. Consider an organism, 2n = 4, with two pairs of homologs. They can make 4 different gametes (long Blue, Short Red) (Long Blue, Short Blue), (Long Red, Short Red), (Long Red, Short blue). Gametes carry thousands of genes, so homologous chromosomes will not be identical over their entire length, even though they may be homozygous at particular loci. Well, the number of gametes can be calculated as 2 n or

F. Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2 n = 8 different gamete types. ABCabc AbcabC aBCAbc AbCaBc

F. Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2 n = 8 different gamete types. And humans, with 2n = 46?

F. Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma Independent Assortment produces an amazing amount of genetic variation. Consider an organism with 2n = 6 (AaBbCc) …. There are 2 n = 8 different gamete types. And humans, with 2n = 46? 2 23 = ~ 8 million different types of gametes. And each can fertilize ONE of the ~ 8 million types of gametes of the mate… for a total 2 46 = ~70 trillion different chromosomal combinations possible in the offspring of a single pair of mating humans.

F. Sexual Reproduction and Variation 1. Meiosis and Mendelian Heredity: The chromosomal theory 2. Solving Darwin’s Dilemma 3. Model of Evolution – circa 1905 Sources of VariationCauses of Change Independent Assortment  VARIATION  NATURAL SELECTION