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Sexual Reproduction And Meiosis 2 Types of Reproduction Asexual Reproduction Sexual Reproduction Increases survival for both plants and animals by passing genetic material within generations. Creates VARIETY in a species by the reassortment (mixing) of DNA. 2 parents = 1 offspring (mixed genetic material) Sexual Reproduction What is Meiosis? The process where 2 cell divisions take place to produce offspring with half the number of chromosomes as the parent cell. Prevents the amount of DNA from continually multiplying in the nucleus. Key Terms • Gonads- sex organs (testes, ovaries) • Gametes- sex cells (sperm, egg) = Sexual Reproduction • Homologous chromosomes - similar chromosome 1 from male parent & 1 from female parent; each has similar gene for same trait. 1 (Position) MOM When Sperm Meets Egg DAD (A gene that occupies a position on a chromosome) Mitochondria DNA Sperm Nucleus • Fertilization - sperm nucleus fuses with egg nucleus. • Zygote - fertilized egg (46 chromosomes) • Diploid - 46 chromosomes (2N) Purpose of Zygote Fertilization To restore the complete number of chromosomes in a species (46). Zygote Sperm • Haploid (monoploid) - 23 chromosomes (n) = 23 46 Ovum Diploid Number (2n) (23) Mitosis (23) = Fertilization (46) 23 + 23= 46 n + n = 2n • • • • • Asexual reproduction 1 parent cell No gametes (no sex cells) Chromosome replicate Type of cell division produces offspring. • Offspring genetically identical. • 2 Daughter cells made (46 chrom. each) • 1 cell division Meiosis • • • • • Sexual reproduction 2 parent cell Gametes present (sex cells) Chromosome replicate Type of cell division produces offspring. • Offspring NOT genetically identical. • 4 Daughter cells made (23 chrom. each) • 2 cell divisions 2 Meiotic Cell Division Synapsis – pairs up 1. Occurs in Gonads ONLY! 2. The pairing up of homologous chromosomes called synapsis. (Prophase 1) Tetrad 3. The 4 chromatid group is called a tetrad. (Prophase 1) 4. Chromosomes cross over to make genetic variations called crossing-over. (Prophase 1) 5. 1st meiotic cell division forms 2 daughter cells. Each a haploid number (n) and already replicated (doubled). (Telophase 1) Meiosis 46 (2n) Nucleus undergoes 2 divisions. 46 Single-stranded double-stranded 6. 2nd meiotic cell division forms 4 haploid cells (n) that are single-stranded chromosomes. (Telophase 2) Meiosis 1 23 23 double-stranded 7. Males: 4 haploid sperms (23 chromosomes each) Females: 1 haploid egg (23 chromosomes) Meiosis 2 single-stranded each Meiosis In Humans 23 (n) 23 (n) 23 (n) 23 (n) 46 46 Males Spermatocyte Females Oocyte 46 1st Division 46 1st Polar Body Meiosis 1 23 23 2nd Division (Spermatozoon) 33 Polar bodies (not functional) 46 Meiosis 2 46 23 23 23 23 3 A dog cell has 78 chromosomes. How many chromosomes would each gamete cell have? 39 Karyotyping An elephant’s gamete has 28 chromosomes in a sperm cell. How may chromosomes would be found in a skin cell? 56 A mosquito has 6 chromosomes. How many would be in an egg cell? 3 Meiosis Paired up by similar traits (seen by bands) + 23 Haploid 23 Haploid (Egg- Sex Cell) (Sperm Sex Cell) YOU 46 Chromosomes (Diploid) 4 Review: Label Both Diagrams Spermatogenesis or Oogenesis ? Meiosis A. 46 Diploid (Human) B. 23 Haploid (Sex Cell) Animal or Plant cell & Why? Simple Organisms are Bacteria Green Algae Paramecia Does Meiosis in Simple Organisms Happen? Yes! Meiosis Does Occur In Simple Organisms And In Humans 5 Meiosis (Sexual Reproduction) in simple organisms go through a process called Conjugation Paramecium Meets Paramecium Conjugation when a bridge of cytoplasm is formed between a two cells and nuclear material is exchanged. Happens Conjugation In The Paramecium: Where Is The Bridge ? Conjugation In Green Algae: Where Is The Bridge ? 1. External Fertilization Gametes fuse outside the body of the female. Gametes are released in the water. Ex) Aquatic animals (invertebrates, most fish, amphibians) 6 External Fertilization: Salmon Spawning The Pacific Salmon Spawning means when female salmon lays her eggs and the male swims over and releases his sperm over the eggs. How Do Animals Know It Is The Right Time To Mate ? 2. Internal Fertilization Gametes fuse within the body. The zygote remains in the body for fertilization or the zygote is released out of the body. Ex) Land animals (mammals, humans) Exceptions (sharks, lobsters) Animals know through different reproductive adaptations. These adaptations trigger the release of eggs and sperm. 1. Singing 2. Display of special feathers 3. Color patches on the skin 4. Release chemicals called pheromones http://video.google.com/videoplay?docid=1667829135266683314 Meiosis (sex cells) & Mitosis (body cells) Meiosis Mitosis for human development 7