CELL REPRODUCTION Chapter 8 CHROMOSOMES CELL DIVISION MEIOSIS

WHAT IS DNA? Deoxyribonucleic acid Long thin molecule that stores genetic info In humans- 6 billion pairs of nucleotides If a cell were the size of a basketball, the DNA would stretch for 40 miles!

CHROMOSOME STRUCTURE DNA is coiled into very compact structures called chromosomes. CHROMOSOMES are rod-shaped structures of DNA + histone PROTEIN.

Replicated DNA Each half of the chromosome is called a CHROMATID. (divide it vertically) Identical chromatids formed during S phase of the cell cycle ensure that cell division will result in indentical cells. They are connected at the CENTROMERE. Draw and label this chromosome

CHROMOSOME NUMBER Each species has a certain number of chromosomes in each cell. For each chromosome there are two copies- one from Mom & one from Dad. For example, humans have 46 and gorillas have 48! Cats, like mine… Pele, have 32 of them!

HOMOLOGOUS Chromosomes Every cell of an organism produced by sexual reproduction has two copies of each autosome. Get one copy of each autosome from each parent. Two copies of each chromosome that contain the same genes are called HOMOLOGOUS.

KARYOTYPE photomicrograph of all the chromosomes in the nucleus of a cell AUTOSOMES are the chromosomes besides the sex chromosomes- numbered In humans, 44 chromosomes are AUTOSOMES and the other 2 are sex chromosomes. What sex chromosome combination do males have?

SEX chromosomes Sex Chromosomes determine the sex of an organism. In humans: XX is female XY is male * This is why males determine the sex of the baby!

Haploid & Diploid Cells Haploid Cells (1n) -have one of each chromosome -examples: sperm cells, egg cells Diploid Cells (2n) -have pairs of chromosomes -examples: all non-reproductive cells. Exception: red blood cells don’t have any chromosomes because they are missing a nucleus!

CELL DIVISION IN PROKARYOTES Prokaryotes have ONE chromosome that exists as a loop. They also have no nuclear envelope separating their DNA from the rest of the cell. BINARY FISSION is the division of a prokaryotic cell (bacteria) into two identical cells! 1.DNA copied 2.Copies move 3.Cell membrane begins to divide the cell in two 4.Two identical haploid cells are formed.

CELL DIVISION IN EUKARYOTES is more complicated because the DNA is enclosed in a nuclear envelope, the DNA is arranged in multiple strands, with a duplicate copy of each chromosome. NUCLEUS divides (karyokinesis) before the cell divides (cytokinesis) Two types: 1.MITOSIS (makes clones) -reproduction of unicellular organisms -addition of cells to a tissue or organ. 2.MEIOSIS (makes gametes) -used for sexual reproduction -1/2 as many chromosomes -sperm & egg can recombine in sexual reproduction.

THE CELL CYCLE The events that occur in the “life” of a cell. The cell grows and copies its’ DNA during Interphase (the longest phase), then divides during M phase. INTERPHASE - G1 (growth) - S (DNA synthesis) - G2 (growth) MITOSIS-nuclear division - prophase - metaphase - anaphase - telophase CYTOKINESIS-cytoplasmic division -cleavage furrow in animal cells - cell plate forms in plant cells.

Question: Where does the toy poodle urinate when it is raining outside? THE PMAT Prophase Metaphase Anaphase Telophase

MITOSIS & MEIOSIS Chapter 8

MITOSIS results in identical cells. Behavior of chromosomes in KARYOKINESIS is simple: sister chromatids separate 1. PROPHASE- replicated DNA condenses into replicated chromosomes (sister chromatids) 2. METAPHASE- replicated chromosomes line up on the metaphase plate (imaginary center plane of cell) 3. ANAPHASE- sister chromatids are pulled apart to opposite “poles” of the cell. 4. TELOPHASE- nuclear envelope reforms. * CYTOKINESIS = 2 cells

Mitosis- produces identical cells MITOSIS Prophase Metaphase Anaphase Telophose CYTOKINESIS

Cleavage furrow in Animal cells. Cell Plate in Plant cells.

Can you name the stages and the organelles involved???

MEIOSIS Process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell. Chromosomes no longer in pairs. This 1/2ing of the chromosome number allows for the fusion of cells later in the life cycle of the organism. The chromosome in one gamete can find its’ “pair” in another gamete through the fusion of sperm & egg. In humans MEIOSIS results in either - 4 sperm cells from 1 sperm producing cell or - 1 egg cell & 3 polar bodies from 1 egg producing cell Egg and Sperm combine chromosomes in sexual reproduction to produce a diploid zygote.

GAMETES- haploid reproductive cells SPERM (spermatogenesis) & EGGS (oogenesis)

MEIOSIS ONE homologous chromosomes separate Genetic recombination Occurs during meiosis 1: 1. Crossing Over 2. Independent assortment Crossing overIndependent assortment

STAGES OF MEIOSIS MEIOSIS 1- homologous replicated chromosomes divide = pairs are split. Prophase 1- DNA condenses into chromosomes Metaphase 1- tetrads align on the metaphase plate Anaphase 1-homologous replicated chromosomes pulled Apart Telophase 1-nuclei form… Q: Cells are haploid or diploid at the end of meiosis 1? A: HAPLOID MEIOSIS 2- chromatids of the replicated chromosomes are separated. Prophase 2-DNA condenses into chromosomes Metaphase 2-replicated chromosomes align on the metaphase plate Anaphase 2-chromatids separate Telophase 2-nuclei form… Q: What does the chromosome behavior in Meiosis 2 remind you of? A: MITOSIS

PROPHASE 1 SYNAPSIS is the pairing of homologous chromosomes. TETRAD is each pair of homologous chromosomes. CROSSING OVER is when portions of chromatids break off and attach to the adjacent chromatid on the homologous chromosome. This results in GENETIC RECOMBINATION!

Crossing Over occurs during PROPHASE 1 of MEIOSIS Homologous chromosomes pair up in a tetrad. Non sister chromatids get tangled and switch places. RECOMBINANT chromosomes are created. = new combinations.

METAPHASE Tetrads align on the metaphase plate. Spindle fibers from one pair of centrioles attach to one replicated chromosome of the tetrad pair. Spindle fibers from the other pair of centrioles attach to the other replicated chromosome of the tetrad pair.

ANAPHASE 1 INDEPENDENT ASSORTMENT is the random separation of the homologous chromosomes based on how the tetrads line up during METAPHASE Think of it as “shuffling” the chromosomes. There are many different combinations of the chromosomes possible… each side gets one out of two of each chromosome. Independent assortment happens during ANAPHASE 1.

CAN YOU FIND THE PATTERN? 1 pair of chromosomes 2 X 1 = 22 kinds of gametes 2 pairs chromosomes 2 X 2 = 44 kinds of gametes 3 pairs Chromosomes 2 X 2 X 2 = 88 kinds of gametes 4 pairs chromosomes 2X2X2X2=1616 kinds of gametes How many kinds of gametes for Humans w/ 23 pairs of chroms?

HOW MANY DIFFERENT TYPES OF GAMETES CAN YOU MAKE? DID YOUR PARENTS MAKE WHEN THEY MADE YOU? WHY DOES THIS MATTER?

FORMULA = (2) 23 or (2) # chromosomes 2 (because there are two copies of each chromosome: one from mom & one from dad) raised to the 23rd power (because humans have 23 chromosomes.) 2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2 x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2 = 8,388,608 1/8,388,608 x 1/8,388,608 = 1/70,368,744,180,000 = that your parents will have another “YOU” YOU ARE SPECIAL!!!

Meiosis II CELLS ARE HAPLOID Although, chromosomes are replicated. Is ESSENTIALLY mitosis. Chromatids separate.

MEIOSIS TWO sister chromatids separate = similar to mitosis. Note the difference… the cells are already haploid. Only one Color of each kind of chromosome in each cell.

MITOSIS QUESTIONS Cell cycle : Interphase (G 1, S, G 2 ) 90% of the cell’s life. It grows and during S phase it copies/replicates it’s DNA) M phase (P,M,A,T) Karyokinesis- division of the nucleus. Replicated chromosomes line up on the metaphase plate and Chromatids are separated. Two identical nuclei are formed. Cytokinesis- division of the cytoplasm via cleavage furrow (microfillaments pulling like a drawstring on sweatpants) in animal cells and cell plate formation (cellulose delivered by vesicles) in plant cells.

2) Fingers = spindle fibers Hands = centrioles Chromosomes don’t move on their own… the microtubules formed by centrioles attach to the centromeres of the replicated chromosomes and move them around. :) 3) The chromosomes are NOT lined up in any particular order during prophase of mitosis.

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