Mitosis is cell division where DNA of daughter cells is exactly the same sequence as parents (daughters are clones)
Meiosis involves tetrad formation and crossing over
Differences btwn meiosis & mitosis: reduction division or multiplication?
Mitosis preserves the ploidy & n # of cell. Always diploid, and alternates btwn 2n and 4n. Multiplication of n number during S phase, division during M phase.
Meiosis is a reduction division. The precursors of gametes are diploid (2n). The resulting cells are haploid. It's when 2 haploid cells meet, it returns to being diploid.
Differences btwn meiosis & mitosis: cycles or non-cycles
Mitosis is a cyclical process. It repeats
Meiosis is a "one-way street"; once cells become gametes, they cannot ever reproduce new cells except by joining another gamete in fertilization
Describe correlation btwn spermatogenesis with mitosis
Recall in males, gametogenesis begins with the stem cell, spermatogonia
Spermatogonia undergo mitosis to produce a clonal population
As long as they stay near the basement membrane, they remain a stem cell and divide by mitosis
Describe the correlation of spermatogenesis and when/how they go through meiosis
If a spermatogonia leave the basement membrane of seminiferous tubule, they begin the process of differentiation.
They become primary spermatocytes (diploid, 4n)
Primary spermatocytes undergo meiosis I to become secondary spermatocytes (haploid, 2n)
In meiosis II, they split their DNA into individual chromatids (1 copy DNA per cell), so they end up haploid, 1n spermatids
They continue further differentiation but no further changes in DNA content is made, so they end up as haploid, 1n spermatids
Explain meiosis I in oogenesis
OOgonia undergo their last mitotic division in female fetus
Meiosis I begins at that time, generating primary oocytes
The primary oocytes lie suspended halfway through meiosis I for 10-50 years.
Each month after menarche, 5-12 primary oocytes respond to hormonal signals
In general, only 1 progresses to 2ndary oocyte
remaining material becomes first polar body
first polar body: the remaining genetic material that is "tossed in the garbage disposal" after a primary oocyte progresses all the way through meiosis 1 to form a secondary oocyte
second polar body: only formed is a spermatozoon penetrates the egg, and the 2ndary oocyte is able to complete meiosis II to become an ovum. Again, the left over genetic material from the reduction division
In what circumstances does a 2ndary oocyte complete meiosis II
Once a primary oocyte completes meiosis I and forms a secondary oocyte, that secondary oocyte begins, but doesn't complete, meiosis II.
Meiosis II is only completed is a spermatozoon penetrates the 2ndary oocyte.
Then it completes meiosis II and becomes an ovum (this also generates the second polar body)
describes the female DNA (n DNA content) and male DNA (n) after an ovum is produced (via penetration of sperm into egg)
They remain separate as male and female pronuclei
Eventually they will fuse to form the diploid zygote (2n)
- of embryonic development
refers to the fusion of the male and female pronuclei to form a zygote
Summarize meiosis I for female
During fetal development, meiosis I begins
After puberty, primary oocytes complete meiosis I, which produces a 2ndary oocyte and a first polar body that may or may not divide again
summarize meiosis II for female
The secondary oocyte begins meiosis II
A secondary oocyte (and first polar body) is ovulated
After fertilization, meiosis II resumes. The oocyte splits into an ovum and a second polar body
Differences btwn male and female gametogenesis
Male: spermatogonia continuously undergo mitosis to generate primary spermatocytes
Meiosis 1 generates 2ndary spermatocytes
Meiosis II generates spermatids
continues throughout lifetime
Female: All oogonia generated b4 birth
Primary oocytes start meiosis I
After completion of meiosis I, just b4 ovulation, Primary oocyte becomes 2ndary oocyte; meiosis II begins
Meiosis II only completed at fertilization
What marks the onset of puberty for both sexes
Also, both are marked by development of 2ndary sexual characteristics