1 / 30

Understanding Sexual Reproduction and Meiosis in Multicellular Organisms

Sexual reproduction is a vital process in the development of multicellular organisms, initiated by the fertilization of an egg cell. This results in a series of cell divisions and differentiation leading to specialized cells, tissues, organs, and systems. The process involves both mitosis and meiosis, where meiosis reduces chromosome number to produce haploid gametes (sperm and egg) that combine to form diploid offspring. This chapter explores the phases of meiosis and the roles of stem cells in differentiation, highlighting how genetic material is exchanged and inherited.

eudora
Download Presentation

Understanding Sexual Reproduction and Meiosis in Multicellular Organisms

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related