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Meiosis and Sexual Reproduction

Meiosis and Sexual Reproduction. Asexual Reproduction. A sexual. “A” = Not. Sexual. Called vegetative reproduction in plants A form of duplication using only mitosis. Example, a new plant grows out of the root or a shoot from an existing plant. Asexual Reproduction.

raphael-bernard
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Meiosis and Sexual Reproduction

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  1. Meiosis and Sexual Reproduction

  2. Asexual Reproduction Asexual “A” = Not Sexual • Called vegetative reproduction in plants • A form of duplication using only mitosis. • Example, a new plantgrows out of the root or a shoot from an existing plant.

  3. Asexual Reproduction • Produces only genetically identical offspring since all divisions are by mitosis. • Offspring called meaning that each is an exact copy of the original organism • This method of reproduction is rapid and effective allowing the spread of an organism • Example: Bacterial growth • Since the offspring are identical, there is no mechanism for introducing . clones diversity

  4. Escherichia coli Paramecium caudatum Asexual Reproduction • In prokaryotes and some one-celled eukaryotes, cells undergo _____ _____ • Hydra reproduce by ________ • Planaria reproduce by ____________ • Several plants reproduce through vegetative reproduction. • Most of these organisms can reproduce sexually as well. binary fission budding fragmentation

  5. Why do organisms have sex? Sexual reproduction increases variety by producing new genetic combinations. • It’s costly to the organism • It’s time-consuming • There are far fewer offspring

  6. Sexual Reproduction Consists of Meiosis and Fertilization • Meiosis: Formation of two haploid sex cells (gametes). • Meiosis is a process to convert a ________ cell to a ________ gamete, and cause a change in the genetic information to increase diversity in the offspring. • In humans, meiosis only occurs in the ________ • Spermatogenesis: In the ______(in males) • Oogenesis: In the _______ (in females) • Fertilization: Combination of genetic information from two separate cells that have one half the original genetic information diploid haploid gonads testes ovaries

  7. Sexual Reproduction + = • Gametes for fertilization usually come from separate parents • Female produces an _____ • Male produces _______ • Both gametes are haploid, with a single set of _____________. • The new individual is called a ______, with two sets of chromosomes (______). • Once the zygote begins to divide, it is called an _______. egg sperm chromosomes zygote diploid embryo

  8. Chromosomes vary from species to species one • Prokaryotes generally have only ___ major chromosome • Consisting of a single circle of DNA • Turkeys have 82! • Giant redwoods have 22! • A tropical fish has the same number of chromosomes as humans, which is ____ 46

  9. Chromosome Characteristics • Diploid set for humans; 2n = 46 • Two types: • Autosomes (#1 – 22) • Sex Chromosomes (#23)

  10. Chromosome Characteristics • Autosomes • Homologous chromosomes • Humans have 22 sets of 2 • One from each parent • Sex chromosomes • Humans have 1 set of 2 • Female-sex chromosomes are homologous (XX) • Male-sex chromosomes are non-homologous (XY)

  11. What can Chromosomes tell us? Scientists can organize chromosomes in a cell into a _________ karyotype • In a karyotype, chromosomes are arranged in order of size, banding pattern, and centromere position: • Let’s see if we can arrange a karyotype together: http://learn.genetics.utah.edu/content/begin/traits/karyotype/

  12. What does this person pass on to the next generation? What sex will this person be?

  13. Meiosis:Reduction/Division Two divisions: Meiosis I & Meiosis II

  14. Like Mitosis: Nuclear membrane disappears Spindles form Chromatin condenses into chromatids Prophase I Unlike Mitosis: • Homologous chromosomes group with other homologous chromosomes to form a “tetrad” • A “chiasma” occurs at the point where the chromosomes cross over

  15. Homologous chromosomes line up at the metaphase plate. Microtubules (spindles) attach to the kinetochore Metaphase I

  16. Anaphase I • Homologous chromosomes separate. • Sister chromatids remain attached.

  17. Telophase I • Two daughter cells are formed with each one containing only one chromosome of the homologous pair. • The daughter cells are now haploid.

  18. Meiosis II:Gamete formation Prophase II: • DNA does not replicate. • Prophase II is just like mitotic prophase.

  19. Metaphase II: • All of the chromosomes line up at the metaphase plate.

  20. Anaphase II: • Centromeres divide • Sister chromatids migrate separately to each pole.

  21. Telophase II: • Cell division is complete. • Four haploid daughter cells are obtained

  22. Summary of Meiosis

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