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Meiosis ii Meiosis ii Presentation Transcript

  • Meiosis 01/06/12 cott Scalpel Please!
  • (I) Sexual Reproduction
    • Two parents give rise to new offspring by the fusion of nuclear materials from two different cells
    • Offspring are not identical to the parent
    • Variations exist, which increases the species ability to adapt to the changing environment
    01/06/12 cott
  • (A) Gonads
    • Sex organs
    • 1. Males – Testes
    • 2. Females – Ovaries
    01/06/12 cott
  • (A) Gametes
    • Sex cells
    • 1. Males – sperm
    • 2. Females – ovum
    01/06/12 cott
  • (B) Fertilization
    • The fusion of the nuclei of one sperm with one ova (egg) to produce a zygote
    • Sperm (n) + Ovum (n) =2n
    • Sperm (23) + Ovum (23) = 46
    01/06/12 cott
  • (C) Haploid
    • Also known as monoploid
    • Represented by: n
    • The gametes contain half the number of chromosomes
    • Sex cells
    01/06/12 cott
  • (D) Diploid
    • Contain the full number (set) of chromosomes
    • 46 in humans!
    • Represented by: 2n
    01/06/12 cott
  • Homologous Chromosomes
    • Pairs of similar chromosomes
    • Humans have 46 chromosomes:
    • 22 pairs of homologous chromosomes
    • 1 pair of sex chromosomes
    01/06/12 cott
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Z S R G z s r g pair of homologous chromosomes
  • (II) Meiosis
    • Known as Reduction Division
    • Meiosis is a type of cell division in which the daughter cell receives only half the number of chromosomes present in the parent cell
    01/06/12 cott
  • 01/06/12 cott
  • Karyotype
    • Chromosomes arranged by pairs.
    • According to:
      • Size
      • Shape
      • General appearance in mitosis: METAPHASE
    01/06/12 cott
  • Fig. 24Ad Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © James King-Holmes/SPL/Photo Researchers, Inc. c. Cells are microscopically examined and photographed. A computer is used to arrange chromosomes by pairs.
  • Chromosomes of human female A Karyotype 01/06/12 cott
  • Chromosomes of human male 01/06/12 cott
  • 01/06/12 cott Species # Species # Fruit fly 8 Guinea Pig 16 Dove 16 Snail 24 Earthworm 36 Tibetan fox 36 Cat 38 Pig 38 Mouse 40 Rat 42 Rabbit 44 Syrian hamster 44 Gorilla 48 Human 46 Ape 48 Sheep 54 Elephant 56 Cow 60 Donkey 62 Horse 64 Dog 78 Chicken 78 Carp 104 Butterflies 380
  • 01/06/12 cott
  • MEIOSIS ANN’Y 01/06/12 cott MEIOSIS INTERACTIVE
  • (III) Stages of Meiosis
    • In meiosis, each cell divides twice:
    • 1. The second stage is very similar to mitosis with the exception that there is:
    • NO replication of chromosomes in the second phase (meiosis 2)
    01/06/12 cott
  • An overview of the stages of meiosis include: 01/06/12 cott
    • One round of chromosome replication
    A first division, where there is no division of centromeres, but where members of a homologous chromosome pair separate from one another A second division, where centromeres divide, sister chromatids separate from one another, and four HAPLOID cells are formed.
  • “ Phases” of Meiosis 01/06/12 cott First Division The reduction division stage Second Division Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II
  • Key
    • SS = single-stranded
    • DS = double-stranded
    01/06/12 cott
  • 01/06/12 cott
  • 01/06/12 cott
  • First Meiotic Division 01/06/12 cott
  • Prophase I
    • Replication of chromosomes into chromatid has already occurred.
    • Each set of chromosomes then pairs up with it’s homologous chromosome.
    • This is known as SYNAPSIS .
    • Each sister chromatid are composed of 2 chromosomes. The “2” sister chromatid(s) make up a “ TETRAD or BIVALENT.”
    01/06/12 cott
  • Prophase I - Variations
    • CROSSING OVER
      • occurs when segments of DNA are exchanged between the chromatid(s) found in tetrads.
    • Point of crossing over: chiasma .
    • Results in recombination of traits
    01/06/12 cott
  • 01/06/12 cott
  • Metaphase I
    • Alignment of the tetrads (4 chromatid) in the middle of the cell (equatorial plane).
    • Line up in homologous pairs!
    01/06/12 cott
  • Anaphase I
    • The homologous chromosomes separate here.
    • Chromosomes are still double stranded( sister chromatid).
    • The process of separating the homologs is known as disjunction.
    01/06/12 cott
  • Telophase I
    • Cytokinesis occurs:
        • 2 daughter cells produced
        • Chromosomes in cells are NOT the same due to CROSSING OVER and INDEPENDENT ASSORTMENT.
    • After this point, the chromosomes WILL NOT replicate.
    • Cells usually start prophase 2 immediately after telophase 1.
    01/06/12 cott
  • 01/06/12 cott
  • Second Meiotic Division 01/06/12 cott
  • Prophase II
    • chromosomes still appear as in prophase I
    • No pairs.
    01/06/12 cott
  • Metaphase II
    • Chromosome (sister chromatid) line up in the MIDDLE of the cell.
    • Single file –DS
    01/06/12 cott
  • Anaphase II
    • DS chromosomes(sister chromatid) separate.
    • Chromosomes move to opposite ends.
    01/06/12 cott
  • Telophase II
    • Both daughter cells undergo cytokinesis forming 4 haploid cells.
    • Will become sex cells.
    • Each cell has ½ the number of chromosomes as the parent.
    01/06/12 cott
    • Meiosis
    • Diploid (2n) cells divide
    • haploid (n) cells
    • These cells mature into specialized reproductive cells (sperm and ova).
    01/06/12 cott Meiosis: An Interactive Animation
  • Meiosis and Variations: Independent Assortment 01/06/12 cott
    • Identifies different combinations of traits.
    • Traits are combined randomly
  • (III) Sexual Reproduction in Animals 01/06/12 cott
  • Gametogenesis
    • Process by which gametes are produced in the gonads
    • Two types:
    • Spermatogenesis
    • Oogenesis
    01/06/12 cott
  • 01/06/12 cott
  • Spermatogenesis
    • Primary spermatocyte goes through first meiotic division and form two daughter cells of equal size
    • Each daughter cell (secondary spermatocyte) goes through the second meiotic division forming four spermatid that will form motile sperm cells of equal size
    01/06/12 cott
  • Oogenesis
    • The primary oocyte goes through first meiotic division.
    • Cytoplasm divide unequally!
    • larger daughter cell: secondary oocyte
    • smaller daughter cell is called the polar body
    • second meiotic division: 1 mature ovum is produced and 2 polar bodies
    01/06/12 cott
  • 01/06/12 cott
    • Comparison of
    • MITOSIS
    • AND
    • MEIOSIS
    01/06/12 cott
  • Comparison: Mitosis and Meiosis 01/06/12 cott
  • 01/06/12 cott
  • USE PREVIOUS TABLES FOR SIMILARITES AND DIFFERENCES 01/06/12 cott
  • Chromosome Abnormalities: Mutations 01/06/12 cott
  • Mutations
    • Appearance of a new trait.
    • Happens in 2 ways:
    • Gene mutation – a new allele for a trait suddenly appears.
    • Chromosome alteration – change in structure.
    01/06/12 cott
  • Chromosomal Abnormalities 01/06/12 cott
  • Nondisjunction 01/06/12 cott
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis I Meiosis II nondisjunction 2n 2n pair of homologous chromosomes normal normal 2n + 1 2n - 1 Zygote Fertilization a.
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Meiosis I Meiosis II nondisjunction pair of homologous chromosomes Zygote 2n + 1 2n + 1 2n - 1 2n - 1 Fertilization b.
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. b. Meiosis I Meiosis II nondisjunction nondisjunction 2n 2n pair of homologous chromosomes pair of homologous chromosomes normal normal 2n + 1 2n - 1 Zygote 2n + 1 2n + 1 2n - 1 2n - 1 Fertilization
  • Down’s Syndrome - Trisomy
      • Extra copy of chromosome 21
      • trisomy 21
      • 47 chromosomes; three copies of chromosome 21
      • Distinct face
      • Mental retardation
    01/06/12 cott
  • 01/06/12 cott Down syndrome male – XY and extra 21
  • 21 extra chromosome 21
  • Turner Syndrome - Monosomy
    • Turner syndrome
    • Female with only 1 X chromosome
    • Monosomy X
    • 45 chromosomes; one X only
    • Short height
    • Usually infertile
    01/06/12 cott
  • 01/06/12 cott 45,X
  • Kleinfelter’s Syndrome - trisomy
    • Male with two X’s and one Y
    • They have 47 chromosomes
    • Tall height
    • Some Female secondary sex characteristics
    • Infertile
    01/06/12 cott
  • 01/06/12 cott
  • 01/06/12 cott 47,XXY
  • Edward Syndrome - Trisomy 18
    • 1 in 8000 births
    • Heart defects
    • Very small
    • Major birth defects
    • Severe mental retardation if survive
    • Often die very young
    01/06/12 cott
  • 01/06/12 cott Female with Trisomy 18 – 47,XX,+18
  • Table 24A
  • Abnormal number of chromosomes causes problems because:
    • Usually we have two copies of each gene.
      • When we have an extra chromosome, we have extra copies of all of the genes on that chromosome.
      • If we have a missing chromosome, we have missing copies of all of the genes on that chromosome.
    01/06/12 cott
  • Amniocentesis, CVS, and InVitro Fertilization
    • Amniocentesis –
        • Used to determine occurrence of Down’s Syndrome.
        • Cells taken from fluid in the Amniotic Sac – after 3 mos.
        • Produce a KARYOTYPE
    • Chorionic Villi Sampling
        • Blood taken from chorion – after 4 weeks
        • Produces KARYOTYPE – screens for genetic diseases
    • IVF – Invitro Fertilization
        • Zygotes or embryo can be screened. Ones with abnormalities removed.
    01/06/12 cott
  • Fig. 24Aa Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. During amniocentesis, a long needle is used to withdraw amniotic fluid containing fetal cells.
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. During chorionic villus sampling, a suction tube is used to remove cells from the chorion, where the placenta will develop.
    • The end
    01/06/12 cott