1 / 20

Meiosis & Sexual Life Cycle

Meiosis & Sexual Life Cycle. Chapter 13. AP Essential Knowledge. Essential knowledge 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization.

chapa
Download Presentation

Meiosis & Sexual Life Cycle

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. Meiosis & Sexual Life Cycle Chapter 13

  2. AP Essential Knowledge Essential knowledge 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization. b. Mitosis passes a complete genome from the parent cell to daughter cells. 4. Mitosis is a continuous process with observable structural features along the mitotic process. • Students must know the order of the processes (replication, alignment, separation).

  3. AP Essential Knowledge • c. Meiosis, a reduction division, followed by fertilization ensures genetic diversity in sexually reproducing organisms. • Gametes have a haploid set of chromosomes • Homologous chromosomes are paired and then separated ensuring haploid set of chromosomes • During meiosis (Prophase I), homologous chromatids exchange genetic material via a process called “crossing over” which increases genetic variation in the resultant gametes.

  4. Homologous Chromosomes • 2 chromosomes that have same length, centromere position, and staining pattern • Autosomes • Non-sex chromosomes • Chromosomes that do not determine gender • Sex Chromosomes • Chromosomes that determine gender

  5. Chromosomes • Human somatic cell = 44 autosomes + 2 sex chromosomes • Human gamete = 22 autosomes + 1 sex chromosome • Sex Chromosomes • Can be XX or XY • XX = Homologous chromosomes • XY = Not homologous chromosomes • Egg must contain X, sperm may contain X & Y • Hence, males determine the gender of offspring

  6. Unnecessary Censorship

  7. Meiosis • 2 Stages of Meiosis • Meiosis I & Meiosis II • Much of Meiosis resembles Mitosis • Chromosomes are replicated only once • Before Meiosis I • 4 daughter cells are produced

  8. Meiosis: An Overview Assume that an organism has: 1 Homologous Pair = 2 Chromosomes (Diploid cell – 2n) STEP 1: Each of the chromosomes is replicated in Interphase STEP 2: Chromosome pairs of copies separate in Meiosis I (Haploid cell – n) BUT 2 copies of each one STEP 3: Each of the copies (sister chromatids) in a cell separates creating 4 haploid cells (Haploid cell with only 1 copy)

  9. What is different in Prophase I? What is different in Anaphase I?

  10. Meiosis I • Prophase I • Longest phase • Homologous pairs align • Crossing-Over may occur • Synapsis – pairing of homologous pairs tied tightly together • Tetrads form (4 chromosomes = 2 pairs) • Each tetrad has 1 or more chiasmata • Criss-crossed regions where crossing over has occurred

  11. Meiosis I (Page 2) • Metaphase I • Tetrads are aligned at the metaphase plate • Each chromosome pair faces a pole • Anaphase I • Homologous chromosomes (composed of 2 copies of each chromosome called chromatids) are pulled apart

  12. What is different between Meiosis I & II? This division is sometimes called the Mitotic division, why?

  13. Meiosis vs. Mitosis • Tetrads align in Prophase I, • Chromosomes align in Prophase mitosis • Chromosomes position @ metaphase plate (Mitosis) • Tetrads position @ metaphase plate (Meiosis) • Homologues separate in Meiosis I • Sister chromatids separate in Meiosis II & Mitosis • Crossing over = Meiosis NOT mitosis

  14. Mitosis Meiosis • DNA replicates in interphase • 1 division • No synapsis • 2 Diploid cells • Genetically identical cells • Responsible for: -- Zygote growth into multicellular organism • DNA only replicates in Pre-meiotic interphase • 2 divisions • Synapsis occurs during prophase I forming tetrads • Crossing over occurs now • 4 haploid cells • Genetically different cells • Responsible for: -- Gamete production -- Genetic variation

  15. Genetic Diversity • The reason for meiosis + sexual reproduction • Mutations are the original source of genetic diversity • 3 main sources of Genetic Diversity 1. Independent Assortment of Chromosomes 2. Crossing Over 3. Random Fertilization

  16.  Each daughter cell has a 50% chance of getting maternal chromosome (or its copy)  Similarly, 50% chance of getting paternal chromosome (or its copy)  Independent assortment - each chromosome is positioned independently of the other chromosomes

  17.  When homologous pairs are formed in Prophase I, a recombinant chromosome can be formed • -- A chromosome that has DNA from 2 different parents  2 chromosome segments trade places (cross over) producing chromosomes with new combos of maternal & paternal genes  1-3 times per chromosome in humans  Increases genetic variation

  18. Random Fertilization • Egg + sperm cells are genetically different from parent cells • Their combination (fertilization) increases variation even more

More Related