Chromosomes, Mitosis, And Meiosis Chapter 8

Do Now What is DNA? Where are your chromosomes located? How many chromosomes do humans have?

DNA DNA – deoxyribonucleic acid Long, thin molecule that stores genetic information Made up of nucleotide building blocks (Adenine, Guanine, Cytosine, Thymine) DNA in a human cell has approximately 6 billion pairs of nucleotides

Chromosomes – rod shaped structures made of DNA and protein

Chromosomes 1. Contained in nucleus 2. When cell is not dividing, genetic info is kept in uncoiled DNA called chromatin 3. When a cell begins to divide the single DNA molecule coils around proteins called histones to form chromosomes

Chromosome Structure 4. Non-histone proteins control activity of specific DNA sequences 5. Each chromosome has two identical parts called – sister chromatids 5. The point at which they meet is called a centromere 6. Division-one chromatid from each chromosome/new cell

Info about Chromosomes 1. Entire human genome mapped – found chromosome location of approximately 23,000 genes 2. Above the centromere is the “p” region (small) 3. Below the centromere is the “q” region (large)

Chromosome Numbers 1. Every Species has a different number of chromosomes 2. Humans have 46 (23 pairs) a. 22 autosomes (do not determine the sex) b. 1 pair sex chromosomes (determine the sex) 3. Females have 2 X chromosomes, males have an X and a Y chromosome

Haploid/Diploid 1. Homologous chromosomes (paired chromosomes) are the same size and shape and carry genes for the same traits 2. Cells with both chromosomes of a homologous pair are considered diploid (2N) – body cells - somatic cells 3. Cells with one of the two chromosomes is considered haploid (N) – sex cells

Haploid/Diploid

Karyotype An arranged photomicrograph of chromosomes that helps determine problems in chromosome # or deletion Karyotypes describe the number of chromosomes, and what they look like under a microscope Attention is paid to: chromosome length position of the centromeres banding pattern differences between the sex chromosomes

Do Now What are chromosomes made of? What does haploid mean? What does diploid mean?

Down’s Syndrome Trisomy 21– 3 copies of chromosome 21 instead of 2 1 in 900 births More common with older mothers Some impairment of cognitive ability and physical growth A particular set of facial characteristics

Down’s Syndrome

Turner Syndrome Female missing one X chromosome (X0) 1 in every 2500 girls Infertile – ovaries do not develop Other female characteristics do not develop Decreased height

Kleinfelter’s Syndrome Male with an extra X chromosome (XXY) Occurs in 1 out of every 1700 men Testicles do not form properly – infertile Delayed motor function and muscle formation Increased height, increased tiredness

Kleinfelter’s Syndrome

II. CELL DIVISION *Virchow – all cells are derived from pre-existing cells *Cell division - the process by which cells produce offspring cells *It is very different for prokaryotes and eukaryotes

Cell Division in Prokaryotes Binary fission – division of a prokaryotic cell into two offspring Single chromosome copies itself Cell grows to 2X its size Cell wall forms between the 2 chromosomes Each new cell is identical

Mitosis - cell division in eukaryotes Division of a cell’s nucleus that produces a genetically identical cell It does not change the amount of DNA in a cell Mitosis occurs in the reproduction of unicellular organisms and in the addition of cells to a tissue or organ of a multicellular organism

Cell Cycle Repeating set of events that make up the life of the cell Consists of: mitosis - cell division interphase G0 Phase – cell exits the cell cycle and does not prepare for another division (nerve cells)

Cell Cycle

Interphase 1. Takes up 80-90% of cells lifespan 2. Three distinct parts: a. G1 (Growth Phase) – cell doubles in size, organelles double in number b. S1 (Synthesis Phase) – chromatin replicates c. G2 (Growth Phase) - rapid growth phase – prepare for next division

Do Now What is cell division in prokaryotes called? What is cell division in eukaryotes called? What are the 4 main phases of the cell cycle?

Mitosis 1. 4 phases: Prophase, Metaphase, Anaphase, Telophase

Prophase 1. Chromatin coils and forms chromosomes, nucleolus and nuclear membrane disappear, centrosomes and spindle fibers appear

Metaphase 1. Chromosomes line up at center, or equator of cell

Anaphase Spindle Fibers pull chromosomes towards poles of cell

Telophase 1. Centrioles and Spindle fibers disappear 2. Chromosomes unwind, and nuclear membrane and nucleolus forms in each cell

Mitosis in Plant Cells (onion)

Cytokinesis 1. Takes place after mitosis 2.Cytoplasm and organelles split and form two daughter cells 3. Each cell receives and identical copy of the original cell’s chromosomes and ~ half of the cytoplasm and organelles

Do Now What are the 4 stages of mitosis? What are the structures that pull the chromosomes toward opposite ends of the cell? How does cytokenesis differ in animals and plants?

Meiosis – reduction division Process of nuclear division that reduces the # of chromosomes in each new cell to half of the original cell This is necessary in reproductive cells called gametes so that they can fuse and form a zygote with a normal # of chromosomes Example – human egg (haploid -1n) and sperm (haploid -1n) form an embryo (diploid -2n)

Meiosis A. Two nuclear divisions take place 1. Meiosis I – homologous chromosomes are separated 2. Meiosis II – chromosomes are separated into chromatids for each haploid cell 3. 4 haploid cells are produced - gametes

Meiosis I – DNA copies itself just before beginning Prophase I - similar to mitosis: DNA coils into chromosomes nuclear membrane and nucleolus disassemble spindle fibers appear THEN Every chromosome lines up with its homologue and forms a tetrad Synapsis – pairing of homologous chromosomes – does not occur in mitosis

Meiosis Helps Genetic Diversity A. During Prophase I, homologous chromosomes line up forming a tetrad B. Chromatids can exchange pieces, called crossing – over C. Genetic recombination results

Meiosis I Metaphase I Tetrads line up randomly along the midline of the cell Spindle fibers attach to centromeres and poles of cell

Meiosis I Anaphase I Each homologous chromosome moves to an opposite pole of dividing cell Independent assortment – the random separation of homologous chromosomes Genetic recombination occurs again due to random separation of maternal (mom’s) and paternal (dad’s) chromosomes

Meiosis I Telophase I Chromosomes reach the opposite ends of the cell Cytokinesis begins New cells are now haploid (1n): they contain only one homologue from each homologous pair But they have two copies of each chromosome because the DNA copied itself right before beginning Meiosis I

Meiosis II DNA does not copy itself before Meiosis II Occurs in both cells formed in Meiosis I Exactly like mitosis Results in four new cells from each cell that began Meiosis Each new cell (haploid – 1n) has half the number of chromosomes as the original cell (diploid – 2n)

Gamete Formation Meiosis produces haploid reproductive cells called gametes Meiosis only occurs in cells of the reproductive organs Humans: Oogenesis - female ovaries produce 1 egg and 3 polar bodies (disintegrate) Spermatogenesis - male testes produce 4 sperm

Oogenesis

Spermatogenesis

Asexual Reproduction Production of offspring from one parent: no union of gametes no genetic diversity offspring genetically identical Unicellular organisms -binary fission or mitosis Multicellular organisms - budding

Sexual Reproduction Production of offspring through meiosis and the union of egg and sperm Offspring are genetically different from parents

Sexual Reproduction Except in identical twins, offspring are unique combinations of their parents’ genes

Sexual Reproduction Gives an evolutionary advantage in an environment that can change – survival of the fittest