Transcript Chapter 21

Using the worksheet received
today complete the first page.
Use your HW to Label the steps
of MEIOSIS, quite
Using the worksheet received
today
complete
the
first
page.
Assessment of Teaching SkillsUse your (ATS-P)
HW to Label the steps
Performance
of MEIOSIS, quite
Chapter 23
Meiosis and
Sexual
Reproduction
Replication
Asexual Reproduction
(review)
• Single parent gives rise to new
offspring by mitotic cell division
• Each new individual receives a set of
chromosomes identical to the parent
chromosomes
• No variation of hereditary information
(I) Sexual Reproduction
• Two parents give rise to new offspring by
the fusion of nuclear materials from two
different cells
• Offspring are not identical to the parent
• Variations exist, which increases the species
ability to adapt to the changing
environment
(A) Reproductive System
• Gonads- specialized organs that
produce gametes
a) ovaries - female gonad
- produce ova (egg)
b) testes - male gonad
- produce sperm cell
Draw a Cell: 2n=6
1. AS it carries out Meiosis
2. Provide 2 KEY characteristics for
each stage
Gametes
• Sex cells
1. Males – sperm
2. Females – ovum
•BOTH ARE MONOPLOID!!!!!!
Comparison of Ova and Sperm
• Egg cells contain stored food in the form
of yolk
• Egg cells are larger than sperm
• Sperm are motile, egg cells are not
• BOTH ARE MONOPLOID!!!!!!
(Remember)
Diploid
• Contain the full number (set)
of chromosomes
• Represented by: 2n
(C)
Haploid
• Also known as monoploid
• Represented by: n
• The gametes contain half the number of
chromosomes
• Remember, gametes are sex cells that
combine to form new offspring. Therefore
gametes are haploid and once they fuse
(combine), they form a zygote that is diploid
Homologous Chromosomes
• Pairs of similar chromosomes
• Humans have 46 chromosomes:
22 pairs of homologous chromosomes
1 pair of sex chromosomes
Homologous Chromosomes
Diploid
2n = 46
Monoploid
n=23
(Sperm/Egg)
Fertilization
• The fusion of the nuclei of one
sperm with one ova (egg) to
produce a zygote
The above image is from
(II)
Meiosis
• Known as Reduction Division
• Meiosis is a type of cell
division in which the daughter
cell receives only half the
number of chromosomes
present in the parent cell
23 Pairs of chromosomes of a human cell
• The chromosomes
labeled X and Y are
the sex
chromosomes
• XX = female
• XY = male
Replication
(III) Stages of Meiosis
• In meiosis, each cell divides twice:
1. The first stage is very similar to
mitosis
2. The second stage is also like mitosis
with the exception that there is
NO replication of chromosomes
Phases of Meiosis
First Division
Second Division
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis
Meiosis
23 Pairs of chromosomes of a human cell
• The chromosomes
labeled X and Y are
the sex
chromosomes
• XX = female
• XY = male
Replication
Key
SS = single-stranded
DS = double-stranded
First Meiotic
Division
Prophase I
• Replication of SS chromosomes
into DS chromosomes
• This is known as synapsis
Metaphase I
• Alignment of the DS
chromosomes in the middle of
the cell
Anaphase I
• DS chromosome separates
• This is known as disjunction
Telophase I
• Cytokinesis occurs and the
nuclear membrane reappears
around the nuclei of the two
newly formed daughter cells
• At this point, the daughter cells
are exact replicas of the parent
cell
Second
Meiotic Division
Prophase II
• Chromosomes DO NOT
replicate
Metaphase II
• Same as metaphase I
Anaphase II
• Same as anaphase I
Telophase II
• Both daughter cells undergo
cytokinesis forming
four haploid cells
• Therefore: As a result of meiosis,
diploid (2n) cells divide and form
haploid (n) cells which mature into
specialized reproductive cells (sperm
and egg)
• Each daughter cell contains half the
number of chromosomes of the original
cell
Using complete sentences,
describe what do YOU FEEL are
the major goals of MITOSIS and
MEIOSIS.
I need to see all of the water
quality group, for tomorrow's trip.
Tuesday: Read and outline pages
307-315
You will need your textbook
tomorrow!!!!!!
I’m
growing
The above image is from
23 Pairs of chromosomes of a human cell
• The chromosomes
labeled X and Y are
the sex
chromosomes
• XX = female
• XY = male
Normal somatic cell
2n = 46
Sperm cell
n=23
Replication
Meiosis
Crossing Over
Crossing Over With Mr. Rizzo
Crossing over
Crossing Over: Two different strands of DNA exchange information
Recombination: result from crossing over, forms
”recombinate chromatids”
Illustration of
crossing-over and
recombination
during the
formation of
gametes or meiosis.
homologous
pair
In meiosis, the
Primary sex cells of
the sperm or ova
must replicate, then
reduce the number
of chromosomes in
half. During the
early stages of cell division in meiosis, two chromosomes of a
homologous pair may exchange segments in the manner shown
above, producing genetic variations in the sex cells.
Meiosis:
Stage Meiosis I
Meiosis 1
Synapsis: like chromosomes match up and align
during Meiosis
chiasma The site where the exchange of chromosome
segments between homologous chromosomes
takes place (crossing-over)
NON DISJUNCTION
Part Two: Meiosis II begins
In ALL FOUR CELLS
n=2
Meiosis for real !!!!!
Meiosis 1
Animation
(360 kb)
Meiosis 2
Animation
(360 kb)
Meiosis for real !!!!!
(III) Sexual Reproduction
in
Animals
Asexual Reproduction
(review)
• Single parent gives rise to new
offspring by mitotic cell division
• Each new individual receives a set of
chromosomes identical to the parent
chromosomes
• No variation of hereditary information
Normal somatic cell
2n = 46
Sperm cell
n=23
Replication
(I) Sexual Reproduction
• Two parents give rise to new offspring by
the fusion of nuclear materials from two
different cells
• Offspring are not identical to the parent
• Variations exist, which increases the species
ability to adapt to the changing
environment
(A) Reproductive System
• Gonads- specialized organs that
produce gametes
a) ovaries - female gonad
- produce ova (egg)
b) testes - male gonad
- produce sperm cell
(B)
Hermaphrodite
• Contain both male and female
reproductive structures
(C)
Gametogenesis
• Process by which gametes are
produced in the gonads
• Two types:
- Spermatogenesis
- Oogenesis
Oogenesis
• The primary oocyte goes
through first meiotic
division and the
cytoplasm of the cell is
divided unequally
• The larger daughter cell
is called the secondary
oocyte and the smaller
daughter cell is called the
polar body
• During second meiotic
division, 1 mature ovum
is produced and 3 polar
bodies
Spermatogenesis
• Primary spermatocyte
goes through first meiotic
division and form two
daughter cells of equal
size
• Each daughter cell
(secondary spermatocyte)
goes through the second
meiotic division forming
four motile sperm cells of
equal size
Comparison of Ova and Sperm
• Egg cells contain stored food in the
form of yolk
• Egg cells are larger than sperm
• Sperm are motile, egg cells are not
(A)
Gametes
• Sex cells
1. Males – sperm
2. Females – ovum
(B)
Fertilization
• The fusion of the nuclei of one
sperm with one ova (egg) to
produce a zygote
• Sperm (n) + Ovum (n) =2n
• Sperm (23) + Ovum (23) = 46
Parthenogenesis
•An embryo develops from an unfertilized egg
•typically involves the development of eggs into viable
offspring from females without fertilization by sperm..
• Parthenogenesis is no longer only for lower invertebrates,
such as aphids, mites and nematode worms--it's also been
found in fish, bees, birds and lizards.
the second polar body -- the daughter cell produced along with the
egg in the second stage of meiosis -- acts like a sperm and re-enters
the egg. Essentially the egg fertilizes itself! As this polar body
contains identical genetic material to the egg, having been produced
by normal division of an already haploid cell, the resulting diploid
cell has only half the genetic diversity of the female's original cells.
Thus fewer bands appear in the DNA fingerprint of the offspring.
Parthenogenesis
Parthenogenesis
but wrong!!!!!
Fertilization
• Union of a haploid
sperm nucleus with a
haploid egg nucleus
– This results in a
diploid zygote with the
full number of
chromosomes
n
n
2n
Fertilization
• Union of a haploid
sperm nucleus with a
haploid egg nucleus
• This results in a
diploid zygote with the
full number of
chromosomes
Fertilization and the Stages of
Mitosis
Two types of Fertilization
External Fertilization
Internal Fertilization
**Parthenogenesis**
External Fertilization
•Eggs are fertilized outside the body
of the female
•Large number of eggs are required
•This type of fertilization is found in
an aquatic environment
Ex: fish and frogs
External Fertilization
External Fertilization
External Fertilization
External Fertilization
What are some differences
between External and
Internal Fertilization?
Provide examples!!!
External Fertilization
External Fertilization
Happy Earth
Day
External Fertilization
External Fertilization
External Fertilization
Internal Fertilization
• Takes place inside the body of
the female
• Less eggs are required
Ex: mammals, birds and reptiles
Internal Fertilization