Cell Division Unit Chapter 10 Section 2 Chapter 11 Section 4

Process of Making a Chromosome Chromosome Supercoils Coils Nucleosome Histones DNA double helix Go to Section: Chromatin – DNA tightly coiled around proteins called Histones Nucleosome – beadlike structure made of chromatin Supercoils – nucleosomes packed together Chromosome – tightly packed supercoils

Chromosomes Made of DNA and Histones (protein) Function : - passes genetic info. from 1 generation to the next Genes- located on chromosomes - information about traits are located here Traits – characteristics passed on by your parents

Chromosomes Numbers Every organism has a specific # of chromosomes Humans = 46 chromosomes The # of chromosomes DOES NOT indicate the COMPLEXITY of an organism Example – a goldfish has 124 chromosomes

Structure of Chromosomes Chromosomes are replicated (copied) before cell division (when a new cells are developed) This makes them visible because they contain TWICE the amount of DNA

Structure of Chromosomes Each chromosome consists of: * CHROMATIDS – identical parts - called “sister chromatids” * CENTROMERE – point at which each chromatid are attached to each other chromatid centromere

Structure of Chromosomes (cont.) When the cell divides into 2 new cells – the “sister chromatids” separate and each one goes into a new cell Each chromosome consists a pair of chromatids (2) Humans = 46 chromosomes = 92 chromatids

Cell Cycle The series of events that cells go through as they grow and divide. During this cycle the cell: 1. grows 2. prepares for division 3. divides to form 2 “daughter” (identical) cells Then each daughter cell prepares to begin the cycle again

Chromosome Quiz 1. Name the 2 substances that make up chromosomes. (2 points) 2. How many chromosomes do humans have? (1 point) 3. What is the function of chromosomes? (1 point) 4. At what point are chromosomes visible in the nucleus? Why? (2 points) 5. Draw and label a chromosome. (4 points)

Events of the Cell Cycle includes is divided into Cell Cycle M phase (Mitosis) Interphase G 1 phaseS phaseProphaseG 2 phaseMetaphaseTelophaseAnaphase Go to Section:

Interphase Longest phase of the cell cycle Known as the “in-between” period of growth Divided into 3 Phases: G 1, S, and G 2

G 1 (Gap 1) Phase Cells do most of their growing during this phase Cells increase in size Manufacturing of new proteins & organelles

S (Synthesis) Phase Chromosomes are replicated Synthesis of DNA molecules & Histones occur

G 2 (Gap 2) Phase Shortest of the phases Organelles & molecules needed for cell division are produced When this phase is complete, cells are ready for the M Phase (mitosis) and begin the process of cell division

Mitosis The 1 st stage of cell division in eukaryotic cells Depending on type of cell, this phase can last from a few minutes to several days. Divided into 4 phases

Prophase The 1 st & longest phase of Mitosis (50 – 60%of whole process) Chromatin condense to form chromosomes Centrioles separate and move to opposite sides of the nucleus structures called SPINDLES begin to form – they help to separate chromosomes Nucleolus disappears & nuclear envelope breaks down

Metaphase Often last only a few minutes Chromosomes line up across the center of the cell Each chromosome is connected to a spindle fiber at its centromere

Anaphase The spindle fibers pull apart the sister chromatids Each chromatid becomes its own chromosome and move towards the centrioles at opposite ends of the cell The phase ends when the chromosomes reach the centrioles & stop moving

Telophase Chromosomes lose their distinct shapes Nuclear envelope re-forms around each group of chromosomes Spindle fibers disappear & a nucleolus becomes visible in each new nucleus Mitosis is complete, but cell division is not

Cytokinesis Cytoplasm pinches in half Each daughter cell has an identical set of chromosomes from the parent cell Usually occurs at the same time as telophase Cell division is not complete until cytokinesis is complete

Overview of Mitosis

Cell Cycle Quiz – 16 points 1. Name the 3 phases of Interphase in order. State the events that occur in each phase. (4 points) 2. What organelles are responsible for cell division? (1 points) 3. What is the longest phase in MITOSIS? (1 point) 4. What event ends cell division? (1 points) 5. What is the final result of Mitosis? (1 point)

6. Label each picture with the correct phase of mitosis (8 points) A B C D

Assignment Complete the following questions in your notebook: chapter assessment p. 257 #’s 3-7, 15-21, 28-34

Homologous Chromosomes Chromosomes that are in all sexually reproducing organisms Occur in pairs 2 identical chromosomes = homologous chromosomes same size and shape. are different than all other chromosomes

Diploid Cells Diploid Cells – contain both chromosomes of a homologous pair Human cell = 23 pairs of homologous chromosomes 2 x 23 = 46 Human Chromosome # = 46

Haploid Cells Haploid Cells – contain only 1 chromosome of a homologous pair 23 pairs of homologous chromosomes 1 x 23 = 23 **all egg & sperm cells = 23 chromosomes ALSO KNOWN AS GAMETES (egg)23 + (sperm) 23 = 46 chromosomes – human baby Zygote – a new cell formed by a sperm & egg cell - has the normal number of chromosomes

MEIOSIS The process of reducing the number of chromosomes per cell in half Separating homologous chromosomes in a diploid cell Making a diploid (46) into a haploid (23)

Process of Meiosis Involves 2 distinct divisions: Meiosis I Meiosis II Begin with 1 diploid cell (46) End with 4 haploid cells (23)

Meiosis I Looks like MITOSIS But in Meiosis I, each chromosome is paired with it corresponding HOMOLOGOUS CHROMOSOME This forms a TETRAD – 4 chromatids ( 2 from each chromosome)

Crossing Over When homologous chromosomes pair up to make tetrads – they exchange portions of their chromatids This is called CROSSING OVER This results in the exchange of genes between the homologous chromosomes This produces new combinations of genes TETRAD

RESULTS OF MEIOSIS I The chromosomes go through the same phases as Mitosis Produces 2 new cells with 46 chromosomes each BUT ……………….. 1. the new “daughter” cells DO NOT have identical sets of chromosomes like the parent 2. are different from each - because of crossing over & the separation of the homologous chromosomes

Meiosis II The 2 cells from Meiosis I enter this 2 nd division Unlike Meiosis I – the 2 cells ….. do not replicate the chromosomes The cells go through each phase just like in Meiosis I

Results of Meiosis II 4 daughter cells that are haploid cells Have only half of the # of chromosomes All are different from each other All are different from its parent cell

Gamete Formation The making of reproductive cells MALE GAMETE = SPERM CELLS Through meiosis – males produce 4 new sperm cells FEMALE GAMETE = EGG CELLS (OVUM) Through meiosis – females produce only 1 egg cell and 3 polar bodies (incomplete)

Gregor Mendel Read handout and section 11-1

Probability & Punnett Squares When Mendel realized when he crossed the pea plant to make hybrids he always had the same result : 75 % - dominant (3/4) 25% - recessive (1/4) He realized that the Principle of Probability could be used to explain the results of genetic crosses.

Probability The likelihood that a particular event will occur Example – flipping a coin What is the probability that the coin will land on heads? What is the probability that the coin will land on tails? This relates to genetics because of the way alleles segregate is completely random, like a coin flip.

Punnett Square Used to predict & compare the genetic variations that will result from a cross. Shows the results of Mendel’s experiment The letters inside & outside represent alleles Outside = parents Inside = possible offspring TTTt tt TtTt Tt

Punnett Squares (cont.) Dominant allele – represented by CAPITAL LETTERS (T) Recessive allele – represented by lower case letters (t)

Homozygous alleles 2 identical alleles Know as the “True Breed” Can be: 1. TT – homozygous dominant 2. tt – homozygous recessive

Heterozygous Alleles 2 different alleles Known as “hybrids” Can be only: 1. Tt

Phenotype Physical characteristics What you see

Genotype Genetic make up What is located on DNA Tt, TT, or tt Tt & TT = tall - each has the same phenotype but have different genotypes

Punnett Square Activity Create Punnett Square for the following crosses: 1. MM x mm6. Bb x bb 2. Pp x Pp7. FF x Ff 3. AA x AA 4. hh x HH 5. rr x rr For each one write the results below each one

Mendel & Punnett Square Quiz – 20 points 1. Define Genetics. 2. Define Heredity. 3. Define Gene. 4. Define Allele. 5. State the Principle Of Dominance. 6. The dominant allele is represented by _____. 7. The recessive allele is represented by ___. 8. Create a Punnett Square for each of thr following. Make sure you state all information for each one: Gg x GGAA x aaRr x RrBb x bb