Meiosis Gamete Formation
Feb 24, 2016
MeiosisGamete
Formation
VocabularyGametes = sex cells (eggs, sperm)Homologous chromosomes =
paired chromosomes (maternal and paternal) that have the same genes
Haploid = Having only one copy of each chromosome (as opposed to diploid, which has two copies of each)
Such chromosome pairs are called homologous chromosomes
(1) Homologues
(2) Alleles - different forms of a gene for a particular trait may occur in homologous chromosomes
anther (where sperm originate)
ovules inside ovary (where eggs originate)
Overview of Meiosis
A. Meiosis - cell division in which the chromosome number is reduced from diploid and gametes are formed
Happens in GAMETES only!!!
Major Events in Meiosis
Meiosis I Produces Diploid Cells
Meiosis II Produces Haploid Cells
PROPHASE I
METAPHASE I ANAPHASE I
TELOPHASE I
Stages of Meiosis
A. Prophase I
1. Synapsis - replicated chromosomes form tetrads
PROPHASE I
METAPHASE I ANAPHASE I
TELOPHASE I
B. Metaphase I - tetrads are aligned at the spindle equator
PROPHASE I
METAPHASE I ANAPHASE I
TELOPHASE I
C. Anaphase I - tetrads split and sister chromatids move toward the spindle poles
PROPHASE I
METAPHASE I ANAPHASE I
TELOPHASE I
D. Telophase I - each daughter cell has a haploid chromosome set
PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II
E. Meiosis II - sister chromatids separate
Meiosis and Genetic Variation A. Crossing over - the exchange of corresponding segments of homologous chromosomes during prophase I
Mitosisand
MeiosisCompare
d
GROWTH MEITOSIS I,CYTOPLASMIC DIVISION
MEIOSIS II,CYTOPLASMIC DIVISION
spermatids (haploid)
secondary spermatocytes
(haploid)
primary spermatocyte
(diploid)
spermato-gonium
(diploid male reproductive
cell)
2. Spermatogenesis - formation of sperm cells
a. Results in production of four spermatids
GROWTH MEITOSIS I,CYTOPLASMIC DIVISION
MEIOSIS II,CYTOPLASMIC DIVISION
spermatids (haploid)
secondary spermatocytes
(haploid)
primary spermatocyte
(diploid)
spermato-gonium
(diploid male reproductive
cell)
b. Spermatids develop a tail to become mature sperm
GROWTH MEITOSIS I,CYTOPLASMIC DIVISION
MEIOSIS II,CYTOPLASMIC DIVISION
ovum (haploid)
primary oocyte (diploid)
oogonium (diploid
reproductive cell) secondary
oocyte haploid)
first polar body
haploid)
three polar bodies
haploid)
3. Oogenesis - formation of egg cells in females
a. Results in one large ovum and three polar bodies
MITOSIS MEIOSISOne division Two divisions
Slide 16
Mitosis
Meiosis I Meiosis II
Figure 10.10Page 172-173
MITOSIS MEIOSISTwo daughter cells Four daughter cells areare produced produced
Slide 16
Mitosis
Meiosis I Meiosis II
Figure 10.10Page 172-173
MITOSIS MEIOSISDaughter cells are Daughter cells contain identical to each other varying combinations of and to parent cell chromosomes
Slide 16
Mitosis
Meiosis I Meiosis II
Figure 10.10Page 172-173