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Sexual Reproduction
And Meiosis
2 Types of
Reproduction
Asexual
Reproduction
Sexual Reproduction
Increases survival for both plants and
animals by passing genetic material within
generations.
Creates VARIETY in a species by the
reassortment (mixing) of DNA.
2 parents = 1 offspring (mixed genetic material)
Sexual
Reproduction
What is Meiosis?
The process where 2 cell divisions
take place to produce offspring with
half the number of chromosomes as the
parent cell.
Prevents the amount of DNA from
continually multiplying in the nucleus.
Key Terms
• Gonads- sex organs (testes, ovaries)
• Gametes- sex cells (sperm, egg)
=
Sexual
Reproduction
• Homologous chromosomes
- similar chromosome 1 from
male parent & 1 from female
parent; each has similar
gene for same trait.
1
(Position)
MOM
When Sperm Meets Egg
DAD
(A gene that
occupies a
position on a
chromosome)
Mitochondria
DNA
Sperm
Nucleus
• Fertilization - sperm nucleus fuses
with egg nucleus.
• Zygote - fertilized egg (46
chromosomes)
• Diploid - 46 chromosomes (2N)
Purpose of Zygote Fertilization
To restore the complete number of
chromosomes in a species (46).
Zygote
Sperm
• Haploid (monoploid) - 23
chromosomes (n)
=
23
46
Ovum
Diploid Number
(2n)
(23)
Mitosis
(23)
=
Fertilization
(46)
23 + 23= 46
n + n = 2n
•
•
•
•
•
Asexual reproduction
1 parent cell
No gametes (no sex cells)
Chromosome replicate
Type of cell division
produces offspring.
• Offspring genetically
identical.
• 2 Daughter cells made
(46 chrom. each)
• 1 cell division
Meiosis
•
•
•
•
•
Sexual reproduction
2 parent cell
Gametes present (sex cells)
Chromosome replicate
Type of cell division
produces offspring.
• Offspring NOT genetically
identical.
• 4 Daughter cells made
(23 chrom. each)
• 2 cell divisions
2
Meiotic Cell Division
Synapsis – pairs up
1. Occurs in Gonads ONLY!
2. The pairing up of homologous chromosomes
called synapsis. (Prophase 1)
Tetrad
3. The 4 chromatid group is called a tetrad.
(Prophase 1)
4. Chromosomes cross over to make genetic
variations called crossing-over. (Prophase 1)
5. 1st meiotic cell division forms 2 daughter cells.
Each a haploid number (n) and already
replicated (doubled). (Telophase 1)
Meiosis
46 (2n)
Nucleus undergoes
2 divisions.
46
Single-stranded
double-stranded
6. 2nd meiotic cell division forms 4 haploid
cells (n) that are single-stranded chromosomes.
(Telophase 2)
Meiosis 1
23
23
double-stranded
7. Males: 4 haploid sperms (23 chromosomes each)
Females: 1 haploid egg (23 chromosomes)
Meiosis 2
single-stranded each
Meiosis In Humans
23
(n)
23
(n)
23
(n)
23
(n)
46
46
Males
Spermatocyte
Females
Oocyte
46
1st Division
46
1st Polar
Body
Meiosis 1
23
23
2nd Division
(Spermatozoon)
33
Polar bodies
(not functional)
46
Meiosis 2
46
23
23
23
23
3
A dog cell has 78
chromosomes. How many
chromosomes would each
gamete cell have?
39
Karyotyping
An elephant’s
gamete has 28
chromosomes in a
sperm cell. How
may chromosomes
would be found in
a skin cell? 56
A mosquito has 6
chromosomes. How
many would be in an
egg cell?
3
Meiosis
Paired up by
similar traits (seen
by bands)
+
23 Haploid
23 Haploid
(Egg- Sex Cell)
(Sperm Sex Cell)
YOU
46 Chromosomes
(Diploid)
4
Review: Label Both Diagrams
Spermatogenesis or Oogenesis ?
Meiosis
A.
46 Diploid
(Human)
B.
23 Haploid
(Sex Cell)
Animal or
Plant cell
& Why?
Simple Organisms are
Bacteria
Green Algae
Paramecia
Does Meiosis in Simple
Organisms Happen?
Yes! Meiosis Does Occur In
Simple Organisms
And
In Humans
5
Meiosis (Sexual Reproduction)
in
simple organisms go through
a process called
Conjugation
Paramecium Meets Paramecium
Conjugation
when a bridge of
cytoplasm is formed between a
two cells and nuclear material
is exchanged.
Happens
Conjugation In The Paramecium:
Where Is The
Bridge ?
Conjugation In Green Algae:
Where Is The Bridge ?
1. External Fertilization
Gametes
fuse outside the body of
the female. Gametes are released in
the water.
Ex) Aquatic animals (invertebrates, most
fish, amphibians)
6
External Fertilization:
Salmon Spawning
The Pacific Salmon
Spawning means when female salmon lays
her eggs and the male swims over and
releases his sperm over the eggs.
How Do Animals Know It Is The
Right Time To Mate ?
2. Internal Fertilization
Gametes fuse within the body.
The zygote remains in the body for
fertilization or the zygote is released out
of the body.
Ex) Land animals (mammals, humans)
Exceptions (sharks, lobsters)
Animals know through different
reproductive adaptations. These
adaptations trigger the release of eggs and
sperm.
1. Singing
2. Display of special feathers
3. Color patches on the skin
4. Release chemicals called
pheromones
http://video.google.com/videoplay?docid=1667829135266683314
Meiosis (sex cells) & Mitosis (body cells)
Meiosis
Mitosis
for
human
development
7