Sexual and Asexual

Reproduction

Coach Book Lesson 9Getting 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,

• 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.

NEW

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.

46

92

4646

23 23 23 23These are your sex cells….sperms and eggs!

COPY

SPLITSPLIT

SPLIT SPLIT

MEIOSIS

MEIOSIS

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 Practice1. 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.

2. Which of these organisms almost always reproduces sexually?

a. Bacteriumb. Animalc. Fungid. 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. Buddingb. Conjugationc. Fertilizationd. Spore Formation

Test Practice