Asexual Reproduction

In asexual reproduction, offspring are produced by
only one parent.
Each parent passes ALL of its genes to the
offspring.

Budding Hydra

Binary fission

Asexual Reproduction

Release of
millions of

fungal spores

Advantages of Asexual

Reproduction

a. It is faster.

b. Large numbers of

offspring are
produced.

c. The parent does

not have to find a
mate.

Asexual Reproduction

Disadvantage of Asexual Reproduction

a.

All of the offspring are ___________.

There is ___________ in the offspring.

b. The ability to _____ to a changing environment is

greatly reduced.

exactly alike

no variation

adapt

Sexual Reproduction

Sexual reproduction
requires two parents.
Each parent passes
on HALF its genes to
its offspring.

Male and female parents are required.
The male produces sperm, and
the female produces eggs.

Disadvantages:

a. The parent must find a mate.
b. Very few offspring are

produced.

c. It takes longer.

Advantage of Sexual

Reproduction:

All of the offspring are different.

Sexual reproduction always

b) Fertilization: Union of sperm and egg

c) Zygote: A fertilized egg

involves:
a) Gametes: Sex cells

​What is the correct term for this object?
1. Chicken egg OR
2. Chicken zygote

Cell Division and Chromosome Number

If an organism is the result of
______ reproduction, it will
have ________ of
chromosomes.

One set comes from the
______ and one set comes
from the ______.

sexual

two sets

mother

father

These two sets are called
homologous chromosomes

Homologous chromosomes are the __________ of each
____________, one coming from the female parent and one
coming from the male parent.

two copies

chromosome

Cell Division and Chromosome Number

For example: An adult fruit fly
has 8 chromosomes. Four of
these chromosomes come
from the female parent, and
four of the chromosomes
come from the male parent.
The two sets of chromosomes
are ___________ to one
another.

homologous

Homologous chromosomes ___________________, but

they may have different ___________ of the genes.

carry the same genes

expressions

Cell Division and Chromosome Number

A cell that contains ________
of homologous chromosomes
is said to be “______.”

both sets

diploid

Diploid means that there are
two of each kind of
chromosome in each cell.

The number of chromosomes in a diploid cell is represented by the symbol
2N.

Cell Division and Chromosome

Number

In the fruit fly cell,
______.

“N” is the number of
different
chromosomes that
an organism has.

2N = 8

In humans, 2N = 46.
Human cells contain 23 pairs of homologous
chromosomes.
Diploid cells contain two complete sets of
chromosomes.

Cell Division and Chromosome

Number

Mitosis produces identical daughter cells.
If the mother cell is ______, two identical ___________________
will be produced.

diploid

diploid daughter cells

Chromosome Number in

Gametes

The ________ of sexually
reproducing organisms contain
only a _________ of
chromosomes.
Gametes are said to be …
… “haploid” or 1N.

gametes

single set

Egg and sperm cells must
have ______________ of
chromosomes so that
when __________ occurs,
the ______ will have the
proper _____________.

half the number

fertilization

zygote

diploid number

1N + 1N = 2N

Chromosome Number in Gametes

The ____ that produce eggs and the ____ that produce
sperm, are ___________.

So how do the egg and sperm cells get to be 1N?

MEIOSIS!!

cells

cells

diploid or 2N

Meiosis is a process of
_______________ in
which the number of
chromosomes per cell
is _____________
through the _________
of homologous
chromosomes.

reduction division

reduced by half

separation

Meiosis occurs only in the
production of
__________________.
The purpose of meiosis is to
______ the chromosome
number in the _____________ by
half.
Meiosis, like mitosis, is preceded
by the ______________________.
Unlike mitosis, this replication is
then followed by two divisions,
_____________________.
In meiosis, _____________ will
divide to produce
___________________.

egg and sperm cells

reduce

egg and sperm

replication of chromosomes

meiosis I and meiosis II

one diploid cell

four haploid gametes

Phases of Meiosis

Interphase:

Prior to ________, each chromosome is _________.
It is similar to chromosome replication of mitosis.
Two identical _______________ are held together by a __________.

meiosis I

replicated

sister chromatids

centromere

Phases of Meiosis

Prophase I:

Chromosomes shorten and thicken.
Each chromosome _____ with its corresponding
______________________ to form a ______.
There are _______________________.
This pairing of homologous chromosomes does not occur in
mitosis.

pairs

tetrad

homologous chromosome

four chromatids in a tetrad

Phases of Meiosis

Metaphase I:

________________________________.

Anaphase I:

The _________________ and the pairs move to
opposite sides of the cell.
Sister chromatids ______________ at their centromeres.

remain attached

Tetrads line up at the center of the cell

tetrads break apart

Phases of Meiosis

Telophase I and Cytokinesis:

The cell separates into two cells.
Meiosis I results in two haploid (1N) daughter cells.
Each daughter cell has half the number of chromosomes as
the original cell.
Sister chromatids ______________.

remain attached

**There is no replication of chromosomes by either cell before entering meiosis II.

Phases of Meiosis

Prophase II:

_____________________________________________

Metaphase II:

________________________________________________

The pairs of sister chromatids start toward the center.

Pairs of sister chromatids line up at the center of the cell.

**There is no replication of chromosomes by either cell before entering meiosis II.

Phases of Meiosis

Anaphase II:

_______________________________________________

Telophase II and Cytokinesis:

________________________________________

The sister chromatids move to opposite sides of the cell.

Meiosis II results in four haploid daughter cells.

•One (2N) cell has

divided to produce
four (1N) sex cells.

Importance
of Meiosis

• The chromosome
number of the egg and
sperm is reduced by half
to ensure that the zygote
will have the proper
number of chromosomes.

Importance
of Meiosis

“Crossing Over” During Meiosis

1. During prophase I, each ________________ lines up next to

its __________.

2. This pairing of homologous chromosomes produces

_______.

3. A tetrad consists of ______________.
4. It is possible for the chromatids within a homologous pair

to _____ around one another.
Portions of the chromatids may ________ and attach to
adjacent chromatids.

5. This process is called “____________.”

tetrad

pair of chromatids

homologue

tetrads

four chromatids

twist

break off

crossing over

“Crossing Over” During Meiosis

6. “Crossing over” is the exchange of genetic information

(genes) between segments of homologous
chromosomes during meiosis.

7. The result is that the offspring will receive a new

combination of genetic information.
This leads to variation in the offspring.

Variation leads
to …

… adaptation
and change.

These variations may cause some of the offspring to be
better suited to their environment.

If they are better suited for their environment, it is more likely
that they will survive to reproductive age and pass these
favorable variations on to their offspring.

If the result of crossing over causes the offspring to be
_________ for its environment, it may __________.
Or, if the offspring does survive, it may not be
_______________________.
This means that it may not be able to ____________.
These “___________” genes are not likely to be
passed on to the offspring.

Crossing over leads to evolution.

less suited

not survive

reproductively competitive

secure a mate

unfavorable

Gamete Formation

In males, meiosis results in
four sperm cells.

Meiosis produces four
haploid cells that are
different.

Gamete Formation

In females, four
cells are produced,
but only one will
become a
functional egg cell.

All of the
cytoplasm and all
of the organelles
are put into one
egg cell.

The other three
cells will never be
functional.

Comparison of Mitosis and Meiosis

Mitosis occurs in all
cells of the body
except egg and
sperm.

Meiosis only occurs in
the formation of egg
and sperm.

Mitosis
Meiosis

In meiosis, each diploid cell divides twice
to produce a total of 4 cells.

In mitosis each diploid
cell divides once to
form 2 cells.

Mitosis
Meiosis

In meiosis, each of the
four cells contains half
the number of
chromosomes as the
parent cell.

In mitosis, each new cell
contains the same
number of
chromosomes as the
original cell.

Mitosis
Meiosis

In mitosis, the homologous
pairs do not come together to
form tetrads.

In meiosis, the homologous
pairs do come together to form
tetrads.

While the chromosomes are in
tetrads, crossing over may
occur.

There will be no crossing over in
mitosis.

Mitosis
Meiosis

In meiosis, the four
haploid cells contain
different
combinations of
chromosomes from
each other.

In mitosis, the new
cells contain identical
copies.