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Mitosis vs. Meiosis

Mitosis vs. Meiosis. Asexual vs. Sexual Reproduction. Mitosis. “The replication of the chromosomes and the production of two nuclei in one cell; usually followed by cytokinesis” (736).

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Mitosis vs. Meiosis

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  1. Mitosis vs. Meiosis Asexual vs. Sexual Reproduction

  2. Mitosis • “The replication of the chromosomes and the production of two nuclei in one cell; usually followed by cytokinesis” (736). • Mitosis is the process of one cell dividing into two identical copies of the cell, known as daughter cells. • Mitosis preserves the number of chromosomes that each cell contains (diploid cells - 2N) • Mitosis is used for growth, repair or asexual reproduction.

  3. Asexual Reproduction • New individuals originate from a single parent • Either the parent divides into two (or more) individuals or new individuals arise as buds from the parent’s body • The only genetic changes arise as the result of mutations(chance events that change the DNA of the offspring) • Low genetic diversity.

  4. Asexual reproduction is a form of regeneration. Sponges, starfish and salamanders are well known for regeneration. • http://science.discovery.com/videos/kapow-superhero-science-limb-regeneration.html

  5. Sexual Reproduction • Why does sex exist? 99.9% of organisms bigger than bacteria do it. • It increases diversity of the offspring and species! • More diversity means more resistance to disease, and the ability to adapt to changing circumstances in the environment

  6. Gamete • In humans and many other animals, the gametes (sex cells) are eggs (ova) and sperm. • In flowering plants, these are ovules and pollen (sperm).

  7. Gametes continued • The gametes contain only ½ the genetic information required to make a new individual(Haploid: n) • What would happen if gametes were created through mitosis, and had the normal number of chromosomes? • Consider a gamete like this from an organism with 10 chromosomes….

  8. How many chromosomes? • Gametes are haploid cells, containing 1 complete set of “n” chromosomes. • “n” for humans is 23 • All other body cells are diploid, having “2n” or 2 complete sets of chromosomes. • “Ploidy” refers to how many complete sets of chromosomes there are.

  9. There is often a large difference in the size of male vs. female gametes.

  10. The structure of a chromosome after replication

  11. The chromosomes come in pairs! • Homologous chromosomes are matching pairs of chromosomes, similar in shape and content. • One chromosome of each pair came from the father (sperm), and one came from the mother (egg).

  12. Human chromosomes from skin cells. • This is what stained chromosomes really look like • Chromosomes #1-22 are called autosomes and always make matching pairs • Chromosome #23 is the sex chromomsomeand can be either “X” or “Y”

  13. Karyotype of the human chromosomes. • Geneticists literally match up the homologous chromosomes from a photograph to make a karyotype. • They contain similar genes but from the two different parents. • Humans have 2 sets of 23 chromosomes for a grand total of 46. “n” is 23 for humans.

  14. Males have an X and a Y chromosome #23, so their sperm can either carry and “X” or a “Y” Females have two copies of the “X” chromosome #23, so their eggs always carry an “X”

  15. The sex of the child is therefore determined by the male gamete (sperm)

  16. Meiosis • Haploid (n) cells or “gametes” are formed with meiosis • Meiosis also jumbles up the genetic material • This only happens in your gonads (ovaries or testes) • Meiosis happens in two phases or cell divisions

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  18. Crossing Over! One source of variation between gametes • HUGE jump in genetic diversity! • Chromosomes “mom” or “dad” already have, randomly mix themselves up! • Then they assort randomly into different gametes.

  19. Independent assortment of chromosomes- another source of variation between gametes

  20. Variation from Sexual Reproduction • Three main sources create MILLIONS of options • Crossing over causes mixing BEFORE meiosis separates chromosomes • Independent Assortment during Anaphase (ex: In mom’s egg cells, each of the 23 sets will separate independently…some of her mom’s chromosomes may go to an egg, and some of her dad’s chromosomes) • Random Fertilization: it is random which egg and sperm meet during fertilization

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