Transcript BDOL Interactive Chalkboard

Chapter 11
(combine with ch. 10)
II. Homologous chromosomes
A. Two chromosomes of each pair in a
2N cell=homologous
chromosomes
1. Each pair of homologous
chromosomes has genes for the same
traits (one from ma/one from pa)
III. Meiosis (2N to N)
A. Production (cell division) of N cells
=sex cells/gametes
1. Male gametes=sperm (testes)
a. spermatogenesis-N
2. Female gametes=eggs (ovaries)
a. oogenesis-N
3. Sperm (N) fertilizes an egg (N)=zygote (2N)
N + N = 2N
B. Sexual reproduction
C. Meiosis consists of 2 separate divisions:
meiosis I (reductional) & meiosis
II (equational).
1. Meiosis I begins with one diploid (2N) cell.
2. Meiosis II is simply mitotic process.
3. End of meiosis II = 4 haploid(N) daughter
cells
Diploid & Haploid cells
Chromosome Numbers of Common Organisms
Organism
Body Cell (2n) Gamete (n)
4
Fruit fly
8
Garden pea
14
7
10
Corn
20
12
Tomato
24
Leopard Frog
26
13
Apple
34
17
Human
46
23
Chimpanzee
24
48
Dog
78
39
Adder’s tongue fern
1260
630
D. Phases
1. Interphase I
a. cell replicates its chromosomes
• 2 identical sister chromatids held
together by a centromere
Interphase
2N=4
2. Prophase I
a. homologous chromosomes
coil up (thicken) & nuclear
memb disappears
b. spindle forms
c. tetrad = h.c. line up with each other
gene by gene
d. h.c. actually break & exchange genetic
material-crossing over
* genetic recombination (leads to variation)
* new combi of genes
Homologous chromosomes
Sister chromatids
Tetrad
Nonsister chromatids
Crossing over in tetrad
Gametes
3. Metaphase I
a. centromere of each
chromosome becomes
attached to a spindle
fiber
b. equator = h.c line up in the
middle
Metaphase I
4. Anaphase I
a. h.c. separate & move to opposite ends
of cell (poles)
b. cell elongates
5. Telophase I
a. nuclear memb reappears
b. spindle broken
c. cytokinesis
d. 2 haploid daughter cells
Telophase I
e. each daughter cell has ½ the genetic
information of original cell (parent)
6. Interkinesis
a. no DNA replication
2nd Division similar to Mitosis
7. Prophase II
a. nuc memb disappears
b. centriole replicates
8. Metaphase II
a. chromosomes pulled to
center of cell
b. line up randomly at
equator
Metaphase II
9. Anaphase II
a. centromere of each chromosome
splits
b. sister chromatids separate & move to
opposite poles
10. Telophase II
a. nuclear memb reappears
b. spindles breakdown
c. cytokinesis
*cell furrowing (animal)
d. 4 haploid cells-gametes
*not identical
E. Genetic recombination
1.Genetic recombination=reassortment of
chromosomes & genetic information, either
by crossing over or by independent
assortment of h.c.
a. Prophase I
b. major source of variation among orgs
1. Polyploidy
a. orgs with more than the usual number of
chromosome sets
• polyploidy is rare in animals & almost
always causes death of zygote
IV. Differences between mitosis & meiosis?
•DY