1 / 13

Meiosis

Meiosis. Chapter 11.4. Function of Meiosis. Produces gametes (sex cells) Males – sperm Females – egg or ovum Only occurs in gonads (testes or ovaries) Sperm + egg → zygote (fertilized egg). Chromosome Count. Chromosome number = ploidy number (n)

lysandra-rose
Download Presentation

Meiosis

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 Chapter 11.4

  2. Function of Meiosis • Produces gametes (sex cells) • Males – sperm • Females – egg or ovum • Only occurs in gonads (testes or ovaries) • Sperm + egg → zygote (fertilized egg)

  3. Chromosome Count • Chromosome number = ploidy number (n) • Haploid: Half the normal number of chromosomes (1 set = n) • Diploid: Normal number of chromosomes (2 sets = 2n) • Sperm (n) + Egg (n) → Zygote (2n)

  4. Human Chromosomes • Humans have 2 sets of 23 chromosomes • n = 23 2n = 46 • 22 pairs of autosomes • 1 pair of sex chromosomes • XX = female XY = male • Meiosis makes haploid gametes from diploid cells

  5. Sex chromosomes

  6. Homologous Chromosomes • Each pair of chromosomes are said to be homologous • One from mom and one from dad • Carry the same genes, but different forms of each gene • Ex – both chromosomes may have eye color gene, but one has blue and one has brown

  7. Meiosis • Two cell divisions • Meiosis I (PMAT I) • Homologous chromosomes separate • Results in 2 haploid cells • Meiosis II (PMAT II) • Sister chromatids separate • Results in 4 haploid cells

  8. Prophase I nuclear env. disappears homologous chromosomes pair up Form a tetrad (tetra = four) Metaphase I tetrads line up along cell’s equator Meiosis I

  9. Anaphase I Tetrad splits, homologous chromosomes separate Telophase I Cell splits into two haploid cells Meiosis I

  10. Meiosis II • Similar to mitosis • Prophase II uneventful • Metaphase II • Replicated chromosomes line up at equator • Anaphase II • Sister chromatids separate • Telophase II • Cells divide = 4 haploid gametes

  11. Gametogenesis • Spermatogenesis • 4 tiny haploid sperm • Oogenesis • 1 large haploid egg, 3 small polar bodies

  12. Creating Variation • Meiosis creates genetic variation in two ways: • Random shuffling of chromosomes in Metaphase I • More than 8 million possible gametes • Crossing over in Prophase I • Homologous chromosomes swap pieces of DNA when tightly paired as tetrad

  13. Crossing Over

More Related