1 Sexual Reproduction And Meiosis 2 Types of Reproduction Asexual Reproduction Sexual 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) 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. = Sexual Reproduction • Gonads - sex organs (testes , ovaries ) • Gametes - sex cells (sperm , egg ) • Homologous chromosomes - similar chromosome 1 from male parent & 1 from female parent; each has similar gene for same trait . Key Terms
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1
Sexual Reproduction
And Meiosis
2 Types of
Reproduction
Asexual
Reproduction
Sexual
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)
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.
=Sexual
Reproduction
• Gonads- sex organs (testes, ovaries)
• Gametes- sex cells (sperm, egg)
• Homologous chromosomes
- similar chromosome 1 from
male parent & 1 from female
parent; each has similar
gene for same trait.
Key Terms
2
(A gene that
occupies a
position on a
chromosome)
(Position)MOM DAD
-
When Sperm Meets Egg
Sperm
Nucleus
Mitochondria
DNA
• Fertilization - sperm nucleus fuses
with egg nucleus.
• Zygote - fertilized egg (46
chromosomes)
• Diploid - 46 chromosomes (2N)
• Haploid (monoploid) - 23
chromosomes (n)
Diploid Number
(2n)
Purpose of Zygote Fertilization
�To restore the complete number of
chromosomes in a species (46).
4623
Zygote
Ovum
Sperm
=
= Fertilization
(46)
23 + 23= 46
n + n = 2n
(23)
(23)Mitosis 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
• 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
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Meiotic Cell Division
1. Occurs in Gonads ONLY!
2. The pairing up of homologous chromosomes
called synapsis. (Prophase 1)
3. The 4 chromatid group is called a tetrad.
(Prophase 1)
4. Chromosomes cross over to make genetic
variations called crossing-over. (Prophase 1)
Tetrad
Synapsis – pairs up
5. 1st meiotic cell division forms 2 daughter cells.
Each a haploid number (n) and already
replicated (doubled). (Telophase 1)
6. 2nd meiotic cell division forms 4 haploid
cells (n) that are single-stranded chromosomes.
(Telophase 2)
7. Males: 4 haploid sperms (23 chromosomes each)
Females: 1 haploid egg (23 chromosomes)
Meiosis
�Nucleus undergoes
2 divisions.
Meiosis 1
Meiosis 2
46 (2n)
Single-stranded
23
(n)
23
(n)
23
(n)
23
(n)
23 23double-stranded
single-stranded each
46
double-stranded
Meiosis In Humans
SpermatocyteOocyte
(Spermatozoon)
1st Polar
Body
3
1st Division
2nd Division
3 Polar bodies
(not functional)
Males Females
Meiosis 1
Meiosis 2
46
23 23 23 23
23 23
46
46 46
46
46
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A dog cell has 78
chromosomes. How many
chromosomes would each
gamete cell have?
An elephant’s
gamete has 28
chromosomes in a
sperm cell. How
may chromosomes
would be found in
a skin cell?
A mosquito has 6
chromosomes. How
many would be in an
egg cell?
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56 3
Karyotyping
Paired up by
similar traits (seen
by bands)
Meiosis
23 Haploid(Egg- Sex Cell)
23 Haploid(Sperm Sex Cell)
+
46 Chromosomes
(Diploid)
YOU
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Meiosis
46 Diploid
(Human)23 Haploid
(Sex Cell)
Review: Label Both Diagrams
Spermatogenesis or Oogenesis ?
A. B.
Animal or
Plant cell
& Why?
Simple Organisms are
�Bacteria
�Green Algae
�Paramecia
Yes! Meiosis Does Occur In
Simple Organisms
And
In Humans
Does Meiosis in Simple
Organisms Happen?
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Meiosis (Sexual Reproduction)
� in simple organisms go through
a process called
Conjugation
Conjugation
� Happens when a bridge of
cytoplasm is formed between a
two cells and nuclear material
is exchanged.
Paramecium Meets ParameciumConjugation 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)
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The Pacific Salmon External Fertilization:
Salmon Spawning
�Spawning means when female salmon lays
her eggs and the male swims over and
releases his sperm over the eggs.
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)
How Do Animals Know It Is The
Right Time To Mate ?
� Animals know through different reproductive adaptations. These adaptations trigger the release of eggs and sperm.