Meiosis and Sexual Reproduction Notes from A.P. Biology

I have some old outlines about Meiosis and Sexual Reproduction from my A.P. Biology class in high school

Meiosis- nuclear division reducing chromosome number from diploid to haploid
- produces gametes (egg and sperm)

Sexual Reproduction
-zygote (haploid (2n))

Homologous chromosomes (Homologues)
-alleles (gene)

Genetic Variation (Why important?)
-genetic recombination
+crossing-over during meiosis I

-independent assortment of homologous chromosomes
+randomly line up along metaphase plate during meiosis I

-fertilization
+egg and sperm unite
+chromosomes combine=(223)2=70,368,744,000,000 possible different zygotes (w/ no crossing over!! imagine the diversity)

Mitosis vs. Meiosis
Differences:

1. Meiosis = 2 nuclear divisions Mitosis = 1 nuclear division
2. Meiosis = 4 haploid cells Mitosis = 2 diploid cells
3. Meiosis = genetically different cells Mitosis = genetically identical cells
4. Meiosis = reproductive organs Mitosis = all other body tissues

Compare Meiosis I vs. Mitosis and Meiosis II vs. Mitosis

Human Life Cycle
-gametogenesis
+males = spermatogenesis
*testes contain stem cells (spermatogonia) which become primary spermatocytes (2n) and then undergo spermatogenesis to produce 4 spermatozoa

+females = oogenesis
*ovaries contain stem cells (oogonia) which become primary oocytes and then undergo oogenesis. First division produces a polar body and ssecondary oocyte (n). Second division of secondary oocyte stops at metaphase II and then completes meiosis II after fertilization and results in 3 polar bodies and 1 egg (n).

PHASES OF MEIOSIS

Prophase I
*spindle forms; centrosomes migrate to opposite poles
*nuclear envelope fragments, nucleolus disappears
*homologous chromosomes form bivalent (tetrads)-synapsis
*crossing-over

Metaphase I
*tetrads line up independently along metaphase plate
*kinetochores + kinetochore spindle fibers

Anaphase I
*homologues of each tetrad move to opposite poles

Telophase I
*spindle disappears
*usually accompanied by cytokinesis

Interkinesis- period of time between meiosis I and meiosis II
*similar to interphase of cell cycle; however, no DNA replication

Prophase II
*spindle reforms

Metaphase II
*chromosomes (now haploid) more to metaphase plate

Anaphase II
*sister chromatids separate and move towards opposite poles

Telophase II
*spindle disappears
*nuclear envelope reforms + nucleolus reappears
*accompanied by cytokinesis resulting in 4 haploid daughter cells

When do the cells go from diploid to haploid?
Meiosis I

WOW way to go Misty! Thanks this helped a lot (:

Very helpful page for sure

wowzers. great post this helps a lot!

thx alot great post!

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License