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Meiosis. Heredity. Heredity Passing of genetic traits from parent to offspring Chromosome theory of heredity Chromosomes carry genes Gene = unit of heredity. What Meiosis is all About. Meiosis allows the creation of unique individuals through sexual reproduction. In The Beginning Two.

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Presentation Transcript
heredity
Heredity
  • Heredity
    • Passing of genetic traits from parent to offspring
  • Chromosome theory of heredity
    • Chromosomes carry genes
    • Gene = unit of heredity
what meiosis is all about
What Meiosis is all About
  • Meiosis allows the creation of unique individuals through sexual reproduction.
in the beginning two
In The Beginning Two
  • Reproduction in which there is a re-mixing of the genetic material is called sexual reproduction
  • Two cells, a sperm and an egg, unite to form a zygote, the single cell from which the organism develops
  • Meiosis is the process of producing sperm and eggs (gametes) – the number of chromosomes are halved
gametes are haploid
Gametes Are Haploid
  • Gametes must have half the genetic material of a normal cell
  • If the genetic material in the gametes was not halved, when they combined the zygote would have more genetic material than the parents!
  • Gametes have exactly one set of chromosomes, this state is called haploid (1n)
  • Regular cells have two sets of chromosomes, this state is called diploid (2n)
fertilization results in a diploid zygote

Egg

1n

Haploid

nucleus

Sperm

1n

Haploid

nucleus

Fertilization Results in a Diploid Zygote
fertilization results in a diploid zygote1
Fertilization Results in a Diploid Zygote

Egg

1n

Haploid

nucleus

Sperm

1n

Haploid

nucleus

fertilization results in a diploid zygote2

Haploid

nucleus

Fertilization Results in a Diploid Zygote

Egg

1n

Haploid

nucleus

Sperm

1n

fertilization results in a diploid zygote3

Haploid

nucleus

Fertilization Results in a Diploid Zygote

Egg

1n

Haploid

nucleus

Sperm

1n

slide16

Meiosis 1

Prior to division, amount of DNA doubles

stages of meiosis
Stages of Meiosis
  • http://www.sumanasinc.com/webcontent/animations/content/meiosis.html
independent assortment during prophase i
Independent Assortment during Prophase I
  • The key difference between Mitosis and Meiosis is the way chromosomes uniquely pair and align in Meiosis

Mitosis

The first division of Meiosis

synapsing
Synapsing
  • UNLIKE in mitosis, homologous chromosomes line up next to each other during prophase
  • This process is called synapsing
  • Lined up homologues are called tetrads
slide20

Anaphase 1

  • During anaphase 1, each homologous chromosome is pulled to opposite sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT BREAK.
  • Nuclei may or may not reform following division.
  • Cytokenesis may or may not occur.
meiosis ii
Meiosis II

Chromosomes are NOT

duplicated again between

Meiosis 1 and Meiosis 2

Why not?

meiosis ii1
Meiosis II
  • Prophase 2: spindle reforms and chromosomes move toward the metaphase plate
  • Metaphase 2: sister chromatids lined up on the metaphase plate
  • Anaphase 2: sister chromatids are separated and pulled toward opposite poles of the cell
  • Telophase 2 and Cytokinesis: nuclei form at either pole and each cell is finally divided into two identical daughter cells
independent assortment1
Independent Assortment

Example:

2 chromosomes in haploid

n = 2

2n = 22 = 4 possible combinations

in humans
In Humans

Example: 23 chromosomes in haploid

n = 23

2n = 223 = ~ 8 million possible combinations!

slide32

Prophase 1 – Crossing Over

  • Homologous chromosomes come together
  • Areas of homologous chromosomes connect at areas called chiasmata
slide33

Crossing Over

  • Segments of homologous chromosomes break and reform at similar locations.
  • Results in new genetic combinations of offspring.
  • This is the main advantage of sexual reproduction
random fertilization
Random fertilization
  • At least 8 million combinations from Mum and another 8 million from Dad …
  • >64 trillion combinations for a diploid zygote!!!
oogenesis
Oogenesis
  • The female gamete is called an ovum
  • At birth each female carries a lifetime supply of developing oocytes, each of which is in Prophase I.
  • A developing egg (secondary oocyte) is released each month from puberty until menopause, a total of 400-500 eggs.
oogenesis1
Oogenesis
  • Only one ovum is produced during meiosis
  • Oogenesis places most of the cytoplasm into the large egg. The other cells, the polar bodies, do not develop.
  • All the cytoplasm and organelles go into one egg for nourishment for the young organism that will develop after fertilization.
spermatogenesis
Spermatogenesis
  • The male gamete is called a sperm
  • Four spermatocytes are formed during meiosis
  • Men are busy - meiosis produces roughly 250,000 sperm a day.
slide40

Any

Questions?

references
References

Slides, information and images were taken from the following presentations:

  • cchs.churchill.k12.nv.us/marshk/Notes/meiosis.ppt
  • bioweb.wku.edu/Faculty/Bowker/120/mitosis.html
  • edweb.sdsu.edu/ltca/Mitosis_Meiosis_files/slide0001.htm
  • waukesha.k12.wi.us/South/Bio1/MEIOSIS.htm
  • my-ecoach.com/coaching/meiosis_files/meiosis.ppt
  • www.grisda.org/tstandish/teachers/presentations/High%20School/Meiosis.ppt
  • www.biology.usu.edu/courses/biol1010-podgorski/PPpage.htm