Transcript Sexual Reproduction

Sexual and
Asexual
Reproduction
Coach Book Lesson 9
Getting the Idea
Humans and other animals have a
combination of traits from both
parents. Simpler organisms, such as
bacteria, usually have exactly the same
traits as organisms from which they are
formed.
I. Reproduction in which two parents
produce offspring is known as sexual
reproduction. Organisms that practice
this type of reproduction must produce
sex cells. The male sex cell is called a
sperm , which the sex cell from a female
is called an egg. A sperm cell joins with
an egg cell during a process known as
fertilization.
A. Unlike your body cells, a sex cell has
half the normal number or
chromosomes. This is so that when
the sperm cell fertilizes an egg cell,
the result is a new cell with a complete
set of chromosomes. So,
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•
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A human sperm cell contains 23 chromosomes.
A human egg cell contains 23 chromosomes.
When they join, they form a cell with 46
chromosomes, which is the number of
chromosomes in your body’s cells.
N
E
W
23
23
46
B. Sex cells have half the number of
chromosomes because of a process
called meiosis. During this process,
chromosome pairs separate. Half the
chromosomes go into one sex cell being
made and the other half go into another
sex cell being made.
C. Meiosis increases the genetic variation
of the offspring produced by sexual
reproduction. This is because you never
know which combination of alleles you
are going to end up with. As
chromosomes split up and go into
different cells, they carry the alleles
with them. One allele from each pair
goes into each sex cell being made. The
random way in which the alleles are
arranged means that no two fertilized
eggs carry the same genetic
information.
M
E
I
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S
I
S
46
COPY
92
23
SPLIT
SPLIT
46
46
SPLIT
SPLIT
23
23
23
These are your sex cells….sperms and eggs!
M
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S
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II. Not all organisms reproduce in this
way. Reproduction in which only one
parent produces offspring is called
asexual reproduction. In this type of
reproduction, there is no mixing or
combining of genetic material. The
offspring is genetically identical to its
parent.
A. Bacteria practice asexual reproduction
in a process known as binary fission.
1. First, the parent cell copies its
genetic material.
2. Then, the cell divides into two
cells.
III. Other organisms besides bacteria can
reproduce both ways. Explain how
FUNGI can reproduce:
Asexually (2 ways) – Fungi form
spores that are genetically idential to
the parent ; unicellular yeast practice
budding.
Sexually – Fungi when conditions are
not favorable will grow together and
exchange genetic material and form
spores that are different from their
parents.
B. Bacteria can also reproduce sexually
during a process known as conjugation
by exchanging genetic material with
another bacterium.
SEE IF YOU REMEMBER WHAT YOU READ:
1. Explain the difference between sexual
and asexual reproduction in terms of
the number of parents involved AND
the genetic relationship between the
offspring and its parent.
SEE IF YOU REMEMBER WHAT YOU READ:
2. What are the names of the sex cells
produced in animals and how are they
different from the rest of your body’s
cells?
Test Practice
1. How does asexual reproduction differ
from sexual reproduction?
a. It involves only one parent.
b. It results in a single offspring.
c. It occurs only in organisms that live
in water.
d. It does not involve the copying of
genetic information.
Test Practice
2. Which of these organisms almost
always reproduces sexually?
a.
b.
c.
d.
Bacterium
Animal
Fungi
Protist
Test Practice
3. How are sex cells different from body
cells?
a. They do not contain chromosomes.
b. They contain half the number of
chromosomes.
c. They contain twice the number of
chromosomes.
d. They contain the only chromosomes
in the body.
Test Practice
4. Which process produces offspring
that are genetically identical to the
parent?
a.
b.
c.
d.
Budding
Conjugation
Fertilization
Spore Formation