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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

Meiosis

Sexual Reproduction

mitosis review
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.
notes
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)
how about the rest of us
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!

karyotype
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.
homologous chromosomes
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

how do we make sperm eggs

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

steps of meiosis
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 *

overview of meiosis

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

preparing for meiosis
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

meiosis 1

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!

meiosis 2

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?

trading pieces of dna
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

mitosis vs meiosis1
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
pedigrees
Pedigrees
  • Pedigrees are family trees that show specific traits passed down through each generation.
  • Ms. Greb’s family tree:
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