_________ is used to produce new cells for growth and repair or for generation of clones of an organism during asexual reproduction. _______ is used to generate gametes for use in sexual reproduction. • Meiosis, mitosis • Mitosis, meiosis 7
Gametes are ____, meaning that they carry one of each type of chromosome, while zygotes formed by fertilization are ______ containing two of each type of chromosome. • Haploid, diploid • Monoploid, biploid • Monosomic, disomic • Asexual, sexual 9
If an organism contains 14 chromosomes in each body (somatic) cell, then its gametes each contain __ chromosomes. • 7 • 14 • 21 • 28 8
Which figure shows mitosis? • The figure on the left • The figure on the right • Neither • both 10
Blonde hair Brown hair Blue Eyes A B C D ONE Which of the chromosomes below are homologous to chromosome number one? • A • A and B • B and C • B • C • B and D 10
3 1 4 2 Which of the numbers below best represents a chromatid? • 1 • 2 • 3 • 4 Cell A Cell B 10
3 1 4 2 Which of the numbers below best represents homologous chromosomes? • 1 • 2 • 3 • 4 Cell A Cell B 10
I. Mitosis Review • Before a cell can divide, what must happen to the DNA? • The DNA must replicate! • What is mitosis? • The division of nuclear material in body cells • What type of cell is produced by mitosis? • Body cells • A human skin cell nucleus contains 46 chromosomes. After mitosis, how many chromosomes would be in each new skin cell nucleus? • 46
II. What is meiosis? • Meiosis is when the nuclear material in our sex cells (sperm and egg) divides and forms 4 new nuclei with 1/2 the number of chromosomes as the original cell. • Meiosis is a type of cell division that reduces the number of chromosomes by half.
II. What is meiosis? 46 46 46
Model Meiosis with Pop Beads!! Diploid = 4 chromosomes (2 homolgous pairs) Haploid = 2 chromosomes Gametes should be genetically different due to crossing over and independent assortment.
III. Why does meiosis happen? • Meiosis happens so that sperm and egg cells can be produced so that sexual reproduction can occur. • Sexual reproduction is when two organisms combine their genetic information to produce genetically different offspring(babies). • Do animals reproduce sexually? • Yes • Do plants reproduce sexually? • Yes • Do bacteria reproduce sexually? • No! Bacteria reproduce asexually!
III. Why does meiosis happen? • In order for two organisms to reproduce sexually, they must produce special reproductive cells called sex cells or gametes. Two types of gametes are the ovum (egg), which is produced by the female, and the sperm, which is produced by the male. • When the egg and sperm unite, a new cell called a fertilized egg or a zygote is produced.
IV. Why is meiosis important? • Meiosis is important because it reduces the number of chromosomes and creates gametes (sperm or egg). • Meiosis is also important because it increasesgenetic variation. This means that it increases the differences between people’s DNA so that every person is genetically different.
V. Diploid vs. Haploid • Diploid – cells with 2 sets of chromosomes • 46 total chromosomes / 23 pairs • One pair from mom and one pair from dad • Haploid– cells with one set of chromosomes (23 total chromosomes) • Mitosis produces diploid cells while meiosis produces haploid cells.
VI. What Happens During Meiosis? • Before meiosis, our sex cells go through interphase, where the DNA replicates and the cell grows.
VI. What happens during meiosis? • The cell in which meiosis occurs is called a germ cell. Meiosis occurs in sexual reproduction when a diploid germ cell produces four haploid daughter cells that can mature to become gametes (sperm or egg). • Meiosis is divided into two sets of phases: Meiosis I and Meiosis II
VI. What happens during meiosis? Meiosis I: • There are four parts of Meiosis I; • Prophase I, Metaphase I, Anaphase I and Telophase I.
VI. What happens during meiosis? • The most important part of Meiosis I is Prophase I. During Prophase I, crossing over occurs. • Crossing over is when parts of a chromosome exchange with another chromosome. This occurs with each homologous pair of chromosomes. This is important because it increases genetic variation.
Independent Assortment • Independent Assortment occurs during metaphase I. • Creates genetic variation between gametes • Homologous pairs of chromosomes line up in the middle of the cell in a random order each time.
VI. What happens during meiosis? • Then the 2 daughter cells go through interkinesis, similar to interphase, however the DNA DOES NOT MAKE A COPY. Interkinesis occurs inbetween meisosis I and meiosis II. • Next, Meiosis II begins.
VI. What happens during meiosis? Meiosis II: • There are four parts of Meiosis II; • Prophase II, Metaphase II, Anaphase II and Telophase II.
VI. What happens during meiosis? • At the end of Meiosis II, cytokinesis occurs. • The end result of the entire process of Meiosis (all 8 steps) is four haploid cells.
Cell A Cell B Cell C Cell D Cell A has 4 chromosomes and Cell D has 2 chromosomes. What process created Cell D? • Mitosis • Asexual Reproduction • Fusion • Meiosis 10
Cell A is considered _______ while Cell D is considered ________. • Haploid; Diploid • Tetrad; Diploid • Diploid; Haploid • Homologous; Haploid Cell A Cell B Cell C Cell D 10
Cell A is considered _______ while Cell D is considered ________. • somatic cell; gamete • gamete; somatic cell • stem cell; somatic cell • stem cell; gamete 30
How can we best describe the diagram below? • Two sister chromatids • Homologous chromosomes • One replicated chromosome • Haploid chromsomes 10
What process is best demonstrated by the diagram below? • Anaphase I • Segregation of alleles • Crossing over • Independent assortment 10
Which of the following leads to genetic variation during meiosis? • All of the above (A, B, C, D) • A & B • A & D • A, B, & D • A & C • Crossing Over • DNA replication • Independent assortment • Mitotic spindle formation 10
Mitosis vs. Meiosis • Let’s Compare and contrast!! • http://www.pbs.org/wgbh/nova/miracle/divi_flash.html