PowerLecture:
Chapter 10
Meiosis and Sexual Reproduction
Sexual Reproduction
Chromosomes are duplicated in germ cells
Germ cells undergo meiosis and
cytoplasmic division
Cellular descendents of germ cells
become gametes
Gametes from each parent meet at
fertilization
Leads to diversity
Asexual Reproduction
Single parent produces offspring
All offspring are genetically identical to one
another and to parent
Sexual Reproduction
Involves
Meiosis
Gamete production
Fertilization
Produces genetic variation among
offspring
Homologous Chromosomes
Carry Different Alleles
Cell has two of each chromosome
One chromosome in each pair from
mother, other from father
Paternal and maternal chromosomes carry
different alleles
Sexual Reproduction
Shuffles Alleles
Through sexual reproduction, offspring
inherit new combinations of alleles, which
leads to variations in traits
This variation in traits is the basis for
evolutionary change
FLOWERING PLANT
anther (where
cells that give
rise to male
gametes
originate)
ovules, inside an
ovary (where
cells that give
rise to female
gametes
originate)
Fig. 10-3a, p.156
Chromosome Number
Sum total of chromosomes in a cell
Germ cells are diploid (2n)
Gametes are haploid (n)
Meiosis halves chromosome number
Human
Karyotype
1
2
3
6
7
8
13
14
15
19
20
21
4
9
22
5
10
11
16
17
12
18
XX (or XY)
Fig. 10-4, p.157
Meiosis: Two Divisions
Two consecutive nuclear divisions
Meiosis I
Meiosis II
DNA is not duplicated between divisions
Four haploid nuclei form
Meiosis I
Each homologue in the
cell pairs with its partner,
then the partners
separate
p. 158
Meiosis II
The two sister chromatids of each
duplicated chromosome are separated
from each other
two chromosomes
(unduplicated)
one chromosome
(duplicated)
p. 158
Meiosis I - Stages
Prophase I
Metaphase I Anaphase I
Telophase I
Prophase I
Each duplicated
chromosome pairs with
homologue
Homologues swap
segments (crossing over)
Each chromosome
becomes attached to
spindle
Fig. 10-5, p. 158
Metaphase I
Homologous
Chromosomes are
pushed and pulled
into the middle of
cell
Fig. 10-5, p. 158
Anaphase I
Homologous
chromosomes
segregate
The sister
chromatids remain
attached
Fig. 10-5, p. 158
Telophase I
The chromosomes
arrive at opposite
poles
Usually followed by
cytoplasmic division
Fig. 10-5, p. 158
Prophase II
Microtubules attach
to the kinetochores
of the duplicated
chromosomes
Fig. 10-5, p. 158
Metaphase II
Duplicated
chromosomes line
up at the spindle
equator, midway
between the poles
Fig. 10-5, p. 158
Anaphase II
Sister chromatids
separate to become
independent
chromosomes
Fig. 10-5, p. 158
Telophase II
The chromosomes
arrive at opposite
ends of the cell
A nuclear envelope
forms around each
set of
chromosomes
Four haploid cells
Fig. 10-5, p. 158
MEIOSIS I
plasma
membrane
newly
forming
microtubules
in the
cytoplasm
PROPHASE I
spindle equator
(midway between
the two poles)
METAPHASE I
one pair of
homologous
chromosomes
ANAPHASE I
TELOPHASE I
Fig. 10-5, p.158
there is no DNA replication
between the two divisions
PROPHASE II
MEIOSIS II
METAPHASE II
ANAPHASE II
TELOPHASE II
Fig. 10-5b, p.159
Effect of Crossing Over
After crossing over, each chromosome
contains both maternal and paternal
segments
Creates new allele combinations in
offspring
Plant Life Cycle
sporophyte
zygote
fertilization
diploid
meiosis
haploid
spores
gametes
gametophytes
Fig. 10-8a, p.162
Animal Life Cycle
multicelled
body
zygote
fertilization
diploid
haploid
meiosis
gametes
Fig. 10-8b, p.162
Fertilization
Male and female gametes unite and nuclei
fuse
Fusion of two haploid nuclei produces
diploid nucleus in the zygote
Which two gametes unite is random
Adds to variation among offspring
Factors Contributing to Variation
among Offspring
Crossing over during prophase I
Random alignment of chromosomes
at metaphase I
Random combination of gametes at
fertilization
Mitosis & Meiosis Compared
Mitosis
Functions
Meiosis
Asexual reproduction
Growth, repair
Occurs in somatic
cells
Produces clones
Function
Sexual reproduction
Occurs in germ cells
Produces variable
offspring
Prophase vs. Prophase I
Prophase (Mitosis)
Homologous pairs do not interact with each
other
Prophase I (Meiosis)
Homologous pairs become zippered together
and crossing over occurs
Anaphase, Anaphase I, and
Anaphase II
Anaphase I (Meiosis)
Homologous chromosomes separate from
each other
Anaphase/Anaphase II (Mitosis/Meiosis)
Sister chromatids of a chromosome separate
from each other
Results of Mitosis and Meiosis
Mitosis
Two diploid cells produced
Each identical to parent
Meiosis
Four haploid cells produced
Differ from parent and one another
Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
Crossing over
occurs between
homologues.
Homologous
pairs align
randomly.
Homologues
separate from
their partner.
Cytoplasm
may divide
before
meiosis II.
Fig. 10-11a, p.164
Meiosis II
no interphase and
no DNA replication
between the two
nuclear divisions
Prophase II
Metaphase II
Anaphase II
Telophase II
New spindle All chromosomes Sister chromatids Haploid cells
forms in each
aligned at the
function as
moved to
nucleus.
equator.
gametes or
opposite spindle
spores.
poles.
Fig. 10-11b, p.164
Mitosis
Prophase
A spindle forms;
tethers
chromosomes to
spindle poles.
Metaphase
All chromosomes
aligned at the
spindle equator.
Anaphase
Sister chromatids
moved to
opposite spindle
poles.
Telophase
Two diploid (2n)
nuclei form.
Fig. 10-11c, p.164