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Sexual Reproduction and Meiosis

Sexual Reproduction and Meiosis. Reproduction. Organisms can reproduce asexually -mitosis, fission, & budding. Organisms can also reproduce sexually Two sex cells (usually egg and sperm) join together Males produce sperm, females produce eggs. Sex cells do not have pairs of chromosomes

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Sexual Reproduction and Meiosis

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  1. Sexual Reproduction and Meiosis

  2. Reproduction • Organisms can reproduce asexually -mitosis, fission, & budding

  3. Organisms can also reproduce sexually • Two sex cells (usually egg and sperm) join together • Males produce sperm, females produce eggs

  4. Sex cells do not have pairs of chromosomes • They are called haploid (single- not paired up: sometimes represented as the letter N). • They only have half the number of chromosomes as body cells. • 23 total chromosomes

  5. All other body cells are diploid (paired up: 2N). • Humans have 23 pairs of chromosomes • 46 chromosomes total

  6. When an egg and sperm join together, it is called fertilization. • The resulting cell is called a zygote • The zygote will begin to undergo cell division http://www.exploratorium.edu/imaging-station/gallery.php?Asset=Zebrafish%20development&Group=&Category=Development&Section=Introduction

  7. The zygote formed following fertilization has a diploid set of chromosomes (46 total). • Half (23) from mom, half (23) from dad.

  8. Sexual reproduction occurs when the genes of two parents are combined to form an offspring. • The offspring is a unique genetic combination of its two parents.

  9. So how do we get specialized sex cells with only half the chromosomes?

  10. Meiosis • Meiosis is a process that produces haploid sex cells.

  11. Why does meiosis happen? • Meiosis allows for the production of sex cells so sexual reproduction can occur.

  12. In meiosis I, the nucleus divides and produces two new cells with one duplicated chromosome • Exactly like mitosis.

  13. In meiosis II, the division happens again and the sister chromatids separate, producing four cells with half (haploid) the number of chromosomes of the original nucleus.

  14. The end result of meiosis: • A cell undergoes division twice. • This produces four sex cells, with half the number (haploid) of chromosomes of the original cell

  15. Mitosis vs. Meiosis http://www.youtube.com/watch?v=Ba9LXKH2ztU

  16. Asexual vs. Sexual reproduction • Asexually produced organisms are genetically identical to their parent.

  17. Sexually produced organisms are genetically different from their parent. • This produces unique organisms who may be more (or less) resistant to disease, more (or less) intelligent, more (or less) physical abilities, adaptable to environment, etc. • There is variety among the offspring. • http://www.youtube.com/watch?v=toWK0fIyFlY

  18. Review • What is it called when a sperm joins with an egg? • Fertilization

  19. After the egg is fertilized by the sperm, what is the new cell called? • A zygote

  20. How many chromosomes are in a human sex cell? • 23

  21. How many chromosomes are in a regular human body cell (skin, cheek, liver, muscle, etc) • 46

  22. What are the names of the two sex cells produced by humans? • Egg and sperm

  23. How many times do cells divide in meiosis? • twice

  24. How many new cells are produced from a single cell in meiosis? • four

  25. How many cells are produced from a single cell in mitosis? • Two

  26. Are sex cells haploid or diploid? • Haploid

  27. Name each item in the picture: A G B A- Chromosome B- Nucleus C- Cell D- DNA E- Gene F- Centromere C D E

  28. Why does meiosis happen? • To produce sex cells

  29. Why does mitosis happen? • GRR • Grow- an organism can get bigger • Replace- replaces damaged or old cells • Reproduce- used by some organisms to reproduce asexually

  30. Name each phase of mitosis

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