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Chapter 10A

Chapter 10A. Sexual Reproduction . In the dvlpt of most multicellular organisms, a single cell (fertilized egg) gives rise to many different types of cells, each w/ a different structure & corresponding function. The fertilized egg gives rise to a large # of cells through cell division

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Chapter 10A

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  1. Chapter 10A Sexual Reproduction

  2. In the dvlpt of most multicellular organisms, a single cell (fertilized egg) gives rise to many different types of cells, each w/ a different structure & corresponding function

  3. The fertilized egg gives rise to a large # of cells through cell division • As the cells inc. in # through this division, they also become specialized in structure & function through differentiation • The various types of cells then arrange into tissues which are organized into organs, & finally organ systems

  4. Nearly all of the cells of a multicellular organism have exactly the same chromosomes & DNA • During differentiation, only a specific segment of the DNA is activated • The segment activated deter. the function & structure of the cell • So all cells initially have the potential to become any type of cell • Once a cell differentiates, the process can’t be reversed

  5. Stem Cells are unspecialized cells that continually reproduce &, under the appropriate conditions, can differentiate into 1 or more types of specialized cells • Embryonic Stem Cells – have this ability • Adult Stem Cells are only found in certain areas such as bone marrow **Scientists have discovered under the right lab culture conditions, embryonic & adult, can differentiate

  6. Chromosomes: • It is a structure in the nucleus of a cell consisting of 1 long thread of DNA that is tightly coiled

  7. Types of Reproduction: • Asexual reproduction – when a cell just divides to form 2 identical daughter cells – only 1 parent • In eukaryotic cells, it requires mitosis • Sexual reproduction – the union of a sperm and egg to form an organism that has a combination of DNA from both parents • Since the offspring produced have cells that are diploid (containing 2 sets of chromosomes – 1 from each parent), the gametes (sex cells) must be haploid (containing only 1 of each type of chromosome) • Requires meiosis

  8. Meiosis: • Purpose – to reduce the # of chromosomes • Occurs in 2 steps: • Meiosis I – • Chromosome pairs replicate • Results in 2 haploid daughter cells w/ duplicated chromosomes diff. from the sets in the original diploid cell • Meiosis II – • The haploid daughter cells from Meiosis I divide • Results in 4 haploid daughter cells called gametes (sex cells - egg & sperm) w/ undoubled chromosomes

  9. Meiosis I: • Begins after Interphase in which cells (1) inc. in size, (2) produce RNA, (3) synthesize proteins, & (4) replicate DNA

  10. Meiosis I cont… • Prophase I – • Nuclear membrane breaks down • Centrioles separate from each other & take up positions on the opposite sides of the nucleus • Spindle fibers are produced • Chromosomes pair up & become visible as a cluster of 4 chromatids called a tetrad

  11. Meiosis I cont… • A homologous chromosome pair consists of 2 chromosomes containing the same type of genes • One from the male & one from the female • Each chromosome consists of 2 sister chromatidsattached @ the centromere • Because the homologous chromosome pairs are close to each other, crossing over can occur (the exchange of chromosome genetic material btw pairs)

  12. Meiosis I cont… • Metaphase I: • The chromosomes are attached to the spindle fiber at the centromere& are pulled into the midline (or equator) of the cell in pairs

  13. Meiosis I cont… • Anaphase I: • The chromosome pairs separate, one chromosome to each side of the cell • Each daughter cell will receive only 1 chromosome from each homologous chromosome pair • Sister chromatids remain attached to each other

  14. Meiosis I cont… • Telophase I & Cytokinesis: • Chromosomes gather @ the poles, nuclear membrane may form & the cytoplasm divides ***Each of the 2 daughter cells from meiosis I contains only 1 chromsome (consisting of 2 chromatids) from each parental pair ***Each daughter cell from meiosis I proceeds to meiosis II

  15. Meiosis II • Prophase II: • Spindle fibers form in each of the daughter cells from meiosis I & attaches to the centromeres of the sister chromatids • The chromosomes progress towards the midline of each cell • The nuclear membrane breaks down

  16. Meiosis II cont… • Metaphase II: • Chromosomes, made up of 2 sister chromatids, line up across the center of the cell • Spindle fibers from opposite poles of the cell attach to 1 of each pair of chromatids

  17. Meiosis II cont… • Anaphase II: • The chromosomes separate so that 1 chromatid from each chromosome goes to each pole

  18. Meiosis II cont… • Telophase II & Cytokinesis: • Nuclear membrane forms around each set of chromosomes • The resulting daughter cells are haploid, containing 1 single chromosome from each pair of chromatids • Either from father or mother contributor

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