Meiosis:

• Process of cell division that produces gametes

  • Produces genetic variability in offspring

• Organisms that reproduce sexually

  • Genetics is about the inheritance of traits of the mechanisms by which these traits are passed from parent to offspring.

  • Sex cells fuse during the process of fertilization 

• Cell division "two halves" the number of chromosomes

• Occurs when formin specilized reproduction cells

• Involves two divisions of the nucleus

• Meiosis 1 and Meiosis 2

 

Sexual Reproduction:

1. Meiosis produces gametes

   1. gametes- sex cells

2. Male sex cell- sperm

3. Women Sex Cell- egg

4. Fertilization- 

   1. Sperm + Egg = Zygote

      1. Zygote- fertilized egg

 

 

Chromosome Numbers: 

• Diploid (2N)

  • chromosomes occur in pairs

  • body cells

  • N= 23

  • Humans 2(23) or 46 chromosomes

• Haploid: (N)

  • chromosomes are unpaired

  • gametes- sex cells

  • humans: 23 chromosomes

 

 

Why Meiosis? 

• meiosis increases genetic variation

• during mitosis, the new cellshave exactly the same number and kind of chromosomes as the orginal cell

If you only had Mitosis:

• you have 46 chromosomes

• each gamete would have 46

• your offspring= 92

• your grandchildren= 184

 

• We need a from of division that allows offspring to have the same number of chromsomes as their parents which produces half the number of chromosomes as parent body

• Meiosis occurs ina specialized body cellstaht produce gametes

• 2 Gametes-- make a zygote

 

Homologous Chromosomes:

• paired chromosomes for the same gene for the same trait

• help determine what the organisms "looks" like 

• has 2 genes for the same trait

• each gene is not identical

 

 

Meiosis: 

• occurs in sexual reproduction

• two cell divisions

  • Meiosis 1

  • Meiosis 2

• begins with one diploid cell body

• chromosomes and DNA replicates

  • have sister chromatids

• produces 4 haploid cells

 

Random Fertilzation:

• each gamete produced independently 

  • the zygote froms a new individual is created randomly

  • Fertilization of an egg and sperm is so random that the possible numeber of outcomes is 64 trillion

 

 

 

 

 

Meiosis 1:

1. Prophase 1:

   1. chromosomes coil up and spindle forms

   2. nuclear envelope disintergrates

   3. homologous chromosomes line up

   4. connect to froma tetrau

   5. squeeze tight togeterh so tight =corssing over

      1. severe locations

2. Metaphase 1:

   1. attach the centromeres to spindle fibers

   2. pulled to the middleof the equator

   3. line up as testrades

      1. in mitosis they up individually

3. Anaphase1: 

   1. aplit the tetrades 

   2. homologous chromosomes with the sister chromatids split to opposite ends

      1. in mitosis they split the chromatids

4. Telephase 1: 

   1. nuclear envelpope reforms 

   2. cytoplasm divides in cytokinesis

   3. each cell only has half the gentic information

 

Meiosis 2:

• begins with 2 cells from Meiosis 1

• Same events just include 2 cells

  • Prophase 2: half number of chromosomes

  • Metaphase 2: line up in the middle

  • Anaphase 2: sister chromatids move to opposite sides of pole

  • Telephase 2: produces 4 haploid cells

 

Meosis & Genetic Variation:

• Allows for rapid generation of new genetic combinations

• 3 mechanisms make key contributions to this process

• independent assortment

• crossing over

• random fertilization

 

Independent Assortment:

• Independent Assortment- random distribution of homologous chromosomes

• Location: During Metaphase 1 Meiosis

 

Crossing Over:

• Crossin Over- DNA exchange

• Location: in Prophase 1

 

Meiosis & Gamete Formation:

• Males:

  • spermatogenesis

  • occurs in testes

  • diploid cell increases in size

• Females:

  • oogenesis

  • occurs in ovaries

  • cytoplasm divides unequally during cyotkinesis during Metaphase 1