Meiosis

For Honors Bio Meiosis Review

Prophase 1

Prophase 1

• homologous chromosomes pair up next to each other called a tetrad

Metaphase 1

• independent assortment

Anaphase 1

• homologous chromosomes separate and move to opposite poles of the cell

• Notice sister chromatids stay attached

Telophase 1

• The spindle breaks down

Both Prophases

• Spindle forms and nuclear membrane breaks down

Metaphase 2

Chromosomes line up on equator

Anaphase 2

• sister chromatids are pulled apart by the spindle fibers and move to opposite poles of the cell

Telophase 2

• Chromosomes reach the poles and nuclear membrane reforms, spindle breaks down

Cytokinesis

• Results in 4 new cells, each HAPLOID or “n”, each genetically unique.

Meiosis

the reproduction of of sex cells

Gametes

Sex cells are also known as

Haploid

• Human gametes contain 23 chromosomes- Half the number needed- Called _______ and labeled “n”

Diploid

When sex cells combine at fertilization, the zygote contains 46 chromosomes which is the number needed in humans —- this is called _______ or “2n”

Homologous Chromosomes

same length, same centromere position, and they carry genes that control the same inherited traits.

Asexual Reproduction

• An organism inherits ALL of its chromosomes for 1 parent

• Offspring is genetically identical to its parent— NO VARIATION

Sexual Reproduction

• Genetically unique cells

• Beneficial genes multiply faster over time

Prophase 1

• Each homologous chromosome has 2 sister chromatids

Prophase 1

• Cross over occurs using tetrads which is CRITICAL to genetically unique sex cells (genetic recombination)

Prophase 1

• Homologous chromosomes exchange genetic information

Telophase 1

• 2 new nuclei

• The cell divides—- each now haploid

Metaphase 1

• Chromosomes centromeres attach to spindle fibers

Metaphase 1

• homologous chromosomes chromosomes line up on opposite sides of equator