NOTES: 11.4 - Meiosis
VOCABULARY:Key Concepts:
HomologousTetradWhat happens during the process of meiosis?
DiploidCrossing-overHow is meiosis different than mitosis?
HaploidGametes
Meiosis I and II
Genes, Chromosomes, and Numbers
● Organisms have tens of thousands of that determine ;
● Where are genes??...
!
● a typical chromosome can contain a
● in the “body cells” of animals and most plants, chromosomes occur in pairs;
● one chromosome in each pair came from the female parent, and the other came from the male parent
VOCABULARY:
● Homologous chromosomes = ; 1 came from mom, and the corresponding chromosome came from dad
● Diploid = has (2n); all “body cells” are diploid
● Haploid = (n)
-in the gametes ()
-when egg joins with sperm, the !
GENERAL INFO:
• Meiosis is a specialized type of cell division that occurs in the .
• Meiosis appears much more complicated than mitosis…
-it is really just
-each one of which has strong similarities to mitosis.
INTERPHASE
• Interphase prior to meiosis is to interphase prior to mitosis
• This includes the !
.• Meiotic division will only occur in cells associated with .
• Meiosis I, the first of the two divisions, is often called
it is here that the chromosome number is reduced from 2n () to n ().
-Ex: Humans: diploid number = ______( = )
PROPHASE I
• Prophase I of meiosis is similar to prophase in mitosis
develop
nuclear envelope
Prophase I - Important Events
● Homologous chromosomes to form a
● The sister chromatids press together at points along their length
● It is during this alignment that and temporarily fuse and exchange segments resulting in
Result: chomosomes (consisting of 2 sister chromatids) are no longer just from “mom” or “dad”-
the !!!
More VOCABULARY:
• Tetrad—each chromosome pairs with homologous chromosome
-!
• Crossing over– when chromosomes are in tetrads, they may exchange parts
-This happens in
-Result – increased variety in offspring (a good thing)
METAPHASE I
Here is where the occurs between Metaphase I in meiosis and metaphase in mitosis.
• In Mitosis, all theline up on the metaphase plate in no particular order.
• In Metaphase I (of Meiosis), the chromosome are aligned on either side of the metaphase plate.
ANAPHASE I
• During Anaphase I the
-the are pulled toward each pole of the cell.
TELOPHASE I
● spindle fibers ;
● the nuclear membrane (envelope) may or may not reform, and the .
At the end of Telophase I:
● each daughter cell has a of chromosomes.
● half the total number in the original cell where the chromosomes were present in pairs.
● chromosomes are still in (1 chromosome = )
● While the original cell was diploid (2n), the daughter cells are now haploid (1n).
● This is why Meiosis I is often called reduction division.
Example: if the DIPLOID # = , then the HAPLOID # =
MEIOSIS II
• Meiosis II is quite simple in that it is simply a mitotic division of each of the haploid cells produced in
Meiosis I.
• There is between Meiosis I and Meiosis II
• Meiosis II begins with…
● A new set of spindle fibers forms
● the chromosomes begin to move toward the center of the cell
● !
METAPHASE II
● The chromosomes in each haploid cell align in the center of the cell… !!
ANAPHASE II
● The
● The
-pulls the single chromosomes toward each pole of the cell.
TELOPHASE II
● the
● the chromosomes begin to uncoil, converting back to
● total of , each with half the total number of chromosomes as the original cell.
● followed by
● MALE GAMETES:
-all will eventually develop into
mature, functional sperm cells.
● FEMALE GAMETES: (as seen in life cycles in “higher” organisms)
-the cytoplasm and cellular organelles are divided
-three of the cells will typically abort
-leaves a to develop into a mature egg cell
**usually much larger than a typical sperm cell.