1 / 20

Meiosis

Meiosis. Sexual Reproduction. Mitosis Review. Mitosis: division of somatic (body) cells during the cell cycle. Product = 2 identical daughter cells. Start with 46 chromosomes and ends with 46 chromosomes. 2n = 2n when n = a single chromosome

peyton
Télécharger la présentation

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 Sexual Reproduction

  2. Mitosis Review • Mitosis: division of somatic (body) cells during the cell cycle. • Product = 2 identical daughter cells. • Start with 46 chromosomes and ends with 46 chromosomes. • 2n = 2n when n = a single chromosome • Ie: n = 23 chromosomes and 2n = 46 chromosomes or 23 pairs of chromosomes.

  3. Notes • Meiosis is: The division of sex cells (gametes) • Humans have 46 chromosomes • Fruit fly has 8 chromosomes • Diploid = “two sets” 2nHaploid = “one set” n • Meiosis is division of gametes, while mitosis is division of somatic (body) cells. • There are 2 cell divisions during meiosis. • Gametes (sex cells): • Males = XY • Females = XX • Fertilizations: Joining of a sperm (n) and egg (n) to create a zygote (2n)

  4. How about the rest of us? • What if a complex multicellular organism (like us) wants to reproduce? • joining of egg + sperm • Do we make egg & sperm by mitosis? No! if we did, then…. + 46 92 46 egg sperm zygote Doesn’t work!

  5. Karyotype • A “picture” of our chromosomes used by genetists. • If you remember: our parents gave each of us 1/2 set of chromosomes (23 of them to be exact) to pair up and complete the set (46). • Used by scientists and doctors to look for abnormalities and gender • Pictures are taken during the prophase/metaphase stage of Mitosis. When chromosomes become visible. • Each chromosome is paired up with it’s match and then laid out in order by size and shape.

  6. Homologous chromosomes • Paired chromosomes • both chromosomes of a pair carry “matching” genes • control same inherited characters • homologous = sameinformation single stranded homologouschromosomes diploid2n 2n = 4 double strandedhomologous chromosomes

  7. 46 46 23 23 46 23 23 How do we make sperm & eggs? • Must reduce 46 chromosomes  23 • must reduce the number of chromosomes by half zygote egg meiosis fertilization sperm gametes

  8. Steps of meiosis 1st division of meiosis separateshomologous pairs (2n  1n) “reduction division” • Meiosis 1 • interphase • prophase 1 • metaphase 1 • anaphase 1 • telophase 1 • Meiosis 2 • prophase 2 • metaphase 2 • anaphase 2 • telophase 2 2nd division of meiosis separatessister chromatids (1n  1n) * just like mitosis *

  9. I.P.M.A.T.P.M.A.T Overview of meiosis 2n = 4 interphase 1 prophase 1 metaphase 1 anaphase 1 n = 2 n = 2 metaphase 2 anaphase 2 telophase 2 prophase 2 n = 2 telophase 1

  10. Preparing for meiosis • 1st step of meiosis • Duplication of DNA • Why bother? • meiosis evolved after mitosis • convenient to use “machinery” of mitosis • DNA replicated in S phase of interphaseof MEIOSIS(just like in mitosis) 2n = 6 single stranded 2n = 6 double stranded M1 prophase

  11. 2n = 4 double stranded prophase 1 2n = 4 double stranded metaphase 1 telophase 1 1n = 2 double stranded Meiosis 1 2n = 4 single stranded • 1st division of meiosis separateshomologous pairs synapsis tetrad reduction Repeatafter me! I can’t hear you!

  12. 4 1n = 2 double stranded metaphase 2 1n = 2 single stranded telophase 2 Meiosis 2 • 2nd division of meiosis separatessisterchromatids 1n = 2 double stranded prophase 2 What doesthis divisionlook like?

  13. Meiosis 1 & 2

  14. Trading pieces of DNA prophase 1 • Crossing over • during Prophase 1, sister chromatids intertwine • homologous pairs swappieces of chromosome • DNA breaks & re-attaches synapsis tetrad

  15. Mitosis vs. Meiosis

  16. Mitosis 1 division daughter cells genetically identical to parent cell produces 2 cells 2n  2n produces cells for growth & repair no crossing over Meiosis 2 divisions daughter cells genetically different from parent produces 4 cells 2n  1n produces gametes crossing over Mitosis vs. Meiosis

  17. Pedigrees • Pedigrees are family trees that show specific traits passed down through each generation. • Ms. Greb’s family tree:

  18. How to read a pedigree

More Related