Sexual and Asexual Reproduction

1. Sexual and Asexual Reproduction

2. 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.

3. 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.

4. 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 completeset 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.

5. N E W 23 23 46

6. 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 otherhalf go into another sex cell being made.

7. C. Meiosis increases the geneticvariation 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.

8. 46 M E I O S I S M E I O S I S COPY 92 SPLIT SPLIT 46 46 SPLIT SPLIT 23 23 23 23 These are your sex cells….sperms and eggs!

9. 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 geneticallyidentical to its parent.

10. Bacteria practice asexual reproduction in a process known as binaryfission. 1. First, the parent cell copies its genetic material. 2. Then, the cell divides into two cells.

11. 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.

12. B. Bacteria can also reproduce sexually during a process known as conjugation by exchanging genetic material with another bacterium.

13. 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.

14. 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?

15. Test Practice • How does asexual reproduction differ from sexual reproduction? • It involves only one parent. • It results in a single offspring. • It occurs only in organisms that live in water. • It does not involve the copying of genetic information.

16. Test Practice • Which of these organisms almost always reproduces sexually? • Bacterium • Animal • Fungi • Protist

17. Test Practice • How are sex cells different from body cells? • They do not contain chromosomes. • They contain half the number of chromosomes. • They contain twice the number of chromosomes. • They contain the only chromosomes in the body.

18. Test Practice • Which process produces offspring that are genetically identical to the parent? • Budding • Conjugation • Fertilization • Spore Formation