Meiosis Flashcards
Gamete Formation involves…
Meiosis = reproductive nuclear division
- egg + sperm
What does meiosis produce
Gamete - eggs and sperm
- 1 cell (diploid, 2n) produced dissimilar gametes (each haploid, n)
Steps to gamete formation
Interphase (G1, S, G2)
Meiosis 1
Meiosis 2
What is happening to interphase of Meiosis
Same thing as in Mitosis
Interphase:
- 1) G1: 1 Cell diploid (2n)
- 2) S phase: Replication
- 3) G2 Now sister chromatids
What is happening to the sister chromatids in Meiosis I
Meiosis I:
Sister chromatids go through meiosis 1, and the two daughter cells separate into homologous pairs
(2 cells, each haploid (n), sister chromatids)
Between Meiosis I and II Interkinesis NOT Interphase (no DNA replication)
What is happening to the sister chromatids in Meiosis II
Meiosis II:
Sister chromatids separate
4 cells, each haploid (n)
single copies
Between Meiosis I and II Interkinesis NOT Interphase (no DNA replication)
What are the similarities between Meiosis and mitosis in Prophase I, II
Chromosomes condense (coil up = easy to manipulate)
Nuclear envelope breaks up and nucleoli disappear
Spindle apparatus forms
Kinetochore microtubules capture chromosomes
What are the similarities between Meiosis and Mitosis in Anaphase I, II
Cytokinesis begins
What are the similarities between Meiosis and Mitosis in Telophase I, II
chromosomes decondense to chromatic
nuclear envelope, nucleoli reappear
spindle disassembles
cytokinesis continues - ends after telophase ends
Differences from Mitosis and Meiosis
Meiosis involves reduction division
2n -> n
Differences from Mitosis and Meiosis Prophase I
Diploid (2n)
homologous chromosomes attach together, forming tetrads (4 chromatids in a row)
Crossing over occurs
Differences from Mitosis and Meiosis Metaphase I
23 tetrads line up along the equator
Differences from Mitosis and Meiosis Anaphase I
Diploid (2n)
tetrads (homologous chromosome pairs) separate and migrate to opposite poles
- (1 homologous chromosome with two sister chromatids) goes to each pole
- chromatids DONT seperate
Differences from Mitosis and Meiosis Telophase I
Diploid
put cell together again
nuclear envelope reforms
cleavage furrow occurs
Tetrads
Which phase do they form, what happens to the sister chromatids
Prophase,
this is when the homologous pairs attach together, forming tetrads (4 chomatids in a row)
Crossing over
Which phase does it occur and what happens to the sister chromatids
Prophase I
A peice of sister chromatid exchanges with matching peice from a chromatid of the homologous chromosome I.e non sister chromatid
- this helps increase genetic diversity
ex) you pass on your dads clakc hair with your mom’s blue eyes
What happens after meiosis I and cytokinesis ends
each new cell has 23 different chromosomes
(1/2 the # of chromosomes ) = haploid
- these cells DO NOT have homologous chromosomes
Chromosomes 1-23 from mom OR dad (randomly segregated)
- each with sister chromatids
Cleavage furrow
Which phase does it occur
Telophase I
What happens in Meiosis II
Same as mitosis except with 23 chromosomes instead of 46
Prophase II
Metaphase II - 23 chromosomes line up at equator
Anaphase II - 23 chromatids migrate to each pole
Telophase II
Cytokinesis - same for mitosis and meiosis (begins in anaphase/anaphase I/anaphase II, and continues through telophase, telophase I, telophase II)
Why meiosis?
need to turn diplois germ cells into haploid gametes
From germ cell to intermediate to gamete
Germ cell
primary (1°) oocyte/spermatocyte, 2n
goes through meiosis I and cytokinesis
Intermediate
Secondary (2°) oocyte/spermatocyte, n
goes through meiosis II and cytokinesis
Gamete
ovum/spermatozoon(zoa = one), n
Fertilization
Spermatozoon (n) contacts + penetrates 2° oocyte (n)
triggers completion of Meiosis II in oocyte (n) - becomes ovum egg
then..♂ and ♀ pronuclei unite
then new cell is formed = zygote (2n)
