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

3

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

4

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?

39

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

5

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?

6

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)

7

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.

1. Singing

2. Display of special feathers

3. Color patches on the skin

4. Release chemicals called

pheromoneshttp://video.google.com/videoplay?docid=1667829135266683314

Meiosis (sex cells) & Mitosis (body cells)

Meiosis

Mitosis

for

human

develop-

ment