DNA in the Cell Inside the nucleus are chromosomes, which house DNA Chromosome made from proteins + histones. Coils DNA so it can fit into a cell Each chromosome consists of identical halves called chromatids Center of the chromosome is called the centromere

Number & Types of Chromosomes Sex chromosomes determine the sex of an organism XX = female XY = Male All other chromosomes are called autosomes Homologous Chromosomes Each organism gets two copies of each autosome; 1 from mom and 1 from dad (46 total chromosomes; 23 pairs in humans) Each 2 paired chromosomes are called homologous chromosomes Homologous chromosomes carry genes for the same traits

Homologous Chromosomes

How Many Chromosomes?

CARP- 104 ELEPHANT-56 KANGAROO-12 PINEAPPLE-50 SHRIMP-92 ADDER’S TONGUE FERN-1200

Diploid & Haploid Cells Diploid Cells  Cells with 2 copies of each chromosome Haploid Cells  Cells with 1 copy of each chromosome Most cells in the body are diploid Sex cells (sperm & egg) are haploid

Diploid & Haploid Cells

Why Do Cells Divide? Get too big (take in more nutrients than they can metabolize) Death/ Need replacement Surface to volume ratio; too much volume, not enough surface When do cells divide? Depends on the type of cell (days, weeks, months, some never divide) Cell Cycle  Cells will grow, replicate, and die

Cell Division in Prokaryotes Prokaryote  unicellular bacteria with no nucleus Binary Fission  DNA is replicated, cell doubles in size and splits

Stages of Cell Cycle in Eukaryotes Interphase  Growth Phase G1  Cell growth S  Synthesis/ Replication of DNA G2 -> Final growth Mitosis  DNA, which has been replicated (remember last unit?) needs to be distributed equally to each new cell

Stages of Mitosis Prophase Chromatin condenses (chromosomes) & nucleus disappears Spindle fibers (microtubules) form & move chromosomes Metaphase Spindles align chromosomes in the middle of the cell Anaphase Centromeres divide and sister chromatids split Chromatids move toward opposite poles Telophase Chromosomes arrive at opposite ends of cell Nucleus reappears Spindle disappears Cell splits (cytokinesis)

Stages of Mitosis

Cytokinesis Animal Cell  cleavage furrow pinches one cell into 2 cells Plant Cell  cell plate makes new cell wall; cell splits

Mitosis Animation

Additional Mitosis Vocabulary G0 Phase  Cell is neither growing or dividing Centrioles Create Ropes that pull chromosomes around the cell (make spindle fibers)

Difference Between Plant Cell & Animal Cell Mitosis Plant cells are surrounded by a tough outer case called a cell wall Animal cells are surrounded by a soft outer case called a cell membrane The first 3 stages of mitosis in plant and animal cells are the same Telophase Animal Cell  Formation of a cleavage furrow Plant Cell  Formation of cell plate

Meiosis Vocabulary Diploid Cells  cells with 2 of each type of chromosome (1 from mom and 1 from dad) n= number of pairs of chromosomes Diploid Cells = 2n Zygote = fertilized egg Gametes= haploid sex cells Fertilization= union of egg and sperm Sexual Reproduction  Parents generate specialized sex cells

Meiosis Getting from diploid to haploid cells: Meiosis Where does it occur in humans? Males Testes Females  Ovaries

Meiosis Overview Meiosis I Diploid cells splits into 2 haploid cells Meiosis II 2 haploid daughter cells undergo mitosis Forms 4 haploid sex cells Same as mitosis

Meiosis I Prophase I Homologous chromosomes pair together (called synapsis) Each homologous pair of chromosomes is called a tetrad Some chromatids break off and attach to adjacent homologous chromatids (crossing over) Crossing Over creates new genetic combinations Metaphase I Homologous chromosomes line up in the middle of the cell Anaphase I Homologous CHROMOSOMES move to opposite poles of the cell Random separation of homologous chromosomes is called Independent Assortment Telophase I Chromosomes reach opposite poles of the cell Cytokinesis begins

Meiosis I

Meiosis II 2 haploid cells go through the process of mitosis & cell division End result of meiosis II is 4 haploid cells Gamete Formation In males meiosis creates 4 sperm cells (called spermatids) In females the cytoplasm is unevenly divided so that only 1 big cell is formed, along with 3 other polar bodies

Meiosis II

Meiosis Animation Meiosis Animation