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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

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Meiosis

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  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

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