Meiosis
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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

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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?


Meiosis 1 2

Meiosis 1 & 2


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 meiosis

Mitosis vs. Meiosis


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:


How to read a pedigree

How to read a pedigree


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