Section 8-1 Chromosomes Section 8-2 Cell Division Section 8-3 Meiosis Cell Reproduction Section 8-1 Chromosomes Section 8-2 Cell Division Section 8-3 Meiosis

Section 8-1 Chromosomes Chromosomes are super coiled DNA strands Chromosome Structure Chromosomes are super coiled DNA strands Rod-like structures made of DNA and proteins. Appear as darkened structures in the nucleus

How are chromosomes formed? DNA wraps tightly around proteins called histones DNA coils in a specific way to produce the structure of a chromosome

Chromosome Numbers Two types of Chromosomes Autosomes – all chromosomes that DO NOT determine the sex of an organism Sex Chromosome – determines the sex of an organism Males – XY Females - XX

Homologous Chromosomes Same size, shape and carry genes for the same traits You get one copy of each chromosome from each parent

Karyotype

Haploid & Diploid Cells Diploid (2n)– Cells with 2 sets of chromosomes (normal cells) Humans have 22 autosome pairs & 1 pair of sex chromosomes (46 total) Haploid (n) – cells with 1 set of chromosomes In humans the ONLY cells that are haploid are reproductive cells (sperm & egg)

Section 8-2 Cell Division Prokaryotes Binary fission – prokaryotic cell division, when a cell produces TWO offspring cells DNA Copied Cell Divides Two identical

Eukaryotic Cell Division Cytoplasm and nucleus divides Two types of cell division Mitosis – cells with genetic material identical to the parent cell Occurs in unicellular organisms Occurs in multicellular organisms to add cells to tissues and organs Meiosis – cells with a reduced chromosome number

Mitosis vs. Binary Fission One diploid cell being copied Results in two identical diploid cells Occurs in eukaryotic organisms One haploid cell being copied Results in two identical haploid cells Occurs in prokaryotic organisms

MITOSIS BINARY FISSION

Cell Cycle Repeating set of events that make up the life of a cell Cell Division is ONLY a part of the cell cycle 2 phases - Mitosis & Cytokinesis Interphase – time between cell divisions 3 phases - G1, S, G2

Interphase G1 (growth 1) - new cells are growing before DNA replication S (synthesis) - After cells reach mature size, they replicate the DNA G2 (growth 2) – cells divide the organelles and prepare for mitosis

Mitosis 4 Phases Prophase Metaphase Anaphase Telophase (PMAT)

Prophase First phase of mitosis DNA coils and shortens into chromosomes (a) Chromosomes attach at the centromere Outside the nucleus centrioles (b) form Spindle fibers (c) form which help to divide chromosomes

Metaphase Chromosomes are easier to identify (completely condensed) Second phase of mitosis Chromosomes are easier to identify (completely condensed) Chromosomes are lined up in the middle of the cell

Anaphase Chromatids of each chromosome separate at the centromere Third phase of mitosis Chromatids of each chromosome separate at the centromere Chromatids move toward the poles of the cell (centromere first)

Telophase Final phase of mitosis Chromosomes reach opposite ends, the nuclear envelope reforms Chromosomes begin to uncoil Nucleolus begins to form in each new cell

Cytokinesis Sometimes considered a part of telophase The division of the cytoplasm Animal Cells – Cell membranes pinch INWARD at the cleavage furrow Plant Cells – Cell forms a “cell plate” between the new cells before cell wall forms

Identify the phase of mitosis B D C

Section 8-3 Meiosis Cells prepare for meiosis by undergoing interphase Cells begin meiosis with a duplicate set of chromosomes Cells then divide TWICE to reduce the chromosome number

Meiosis I - Very closely resembles mitosis Prophase I – DNA coils, spindle fibers form Homologous chromosomes pair – SYNAPSIS TETRAD – the pair of homologous chromosomes Metaphase I – tetrads line up at the middle Anaphase I – chromosomes are pulled to the poles Telophase I – chromosomes are at opposite poles AND cytokinesis begins

Events DURING Meiosis I Crossing Over Occurs during Prophase I When portions of chromatids break off and re-attach on homologous chromosomes Permits the exchange of genetic material Independent Assortment Occurs during Anaphase I The random separation of the genetic material Results in genetic recombination

Crossing Over

Meiosis 2 – Reducing Chromosome Number DNA IS NOT COPIED BEFORE MEIOSIS II Prophase II – Spindle fibers form; move chromosomes Metaphase II – chromosomes line up at the middle Anaphase II – chromatids SEPARATE; moves to poles Telophase II – nuclear membranes form around chromosomes Cytokinesis II – cytoplasm divides creating 4 cells w/ ½ chromosome number

In animals – meiosis produced haploid reproductive structures Formation of Gametes In animals – meiosis produced haploid reproductive structures Occurs in the testes and ovaries Spermatogenesis – meiosis in males (testes) Produces spermatids Oogenesis – meiosis in females (ovaries) Produces 1 egg and 3 polar bodies Polar bodies degenerate

Reproduction Asexual reproduction – production of offspring from ONE parent Does not involve the union of sperm and egg Offspring is genetically identical to the parent Sexual reproduction – production of offspring using 2 parents Meiosis Union of sperm and egg