6-1 Outline Notes

  1. Sexualreproduction produces an offspring when genetic materials from two different sex cells combine.
  2. The female sex cell, the egg forms in an ovary.
  3. The male sex cell, the spermforms in a testis
  4. During a process called fertilizationan egg cell and sperm cell join. The new cell that forms is a zygote.
  5. Organisms that reproduce sexually make two kinds of cells -- bodycells and sex cells.
  6. Body cells are diploid; they have pairs of chromosomes.
  7. If a zygote has too many or too few chromosomesit will not develop properly.
  8. Different organisms have different numbersof chromosomes.
  9. Homologouschromosomes are pairs of chromosomes that have genes for the same traits arranged in the same order.
  10. Sex cells are haploidthey have only one chromosome from each pair of chromosomes.
  11. In meiosisone diploid cell divides and makes 4 haploid cells.
  12. Meiosis involves two divisions of the nucleus and the cytoplasmThese divisions, known as meiosis I and II, result in 4 haploid cells
  13. During interphasethe reproductive cell grows and duplicates it chromosomes.
  14. During meiosis I, each pair of duplicated homologous chromosomes lengthenand thicken
  1. After meiosis, the two cells formed during this stage go through a second division of the nucleusand cytoplasm called meiosis II, sister chromatidsseparate to produce four haploid cells.
  2. Meiosis forms sex cells with the correct haploid number of chromosomesThis maintains the correct diploidnumber of chromosomes in organisms when sex cells join.
  3. Meiosis creates genetic variations by producing haploidcells.
  4. During mitosisand cell division, a body cell and its nucleus divide once and produce two identical cells.
  5. During meiosisa reproductive cell and its nucleus divide twice and produce four cells – two pairs of identical haploid cells
  6. Sexual reproduction produces offspringthat have a new combination of DNA. This results in genetic variationamong individuals.
  7. Genetic variation gives individuals within a population slight differences that might be an advantage if the environmentalchanges.
  8. Selectivebreeding has been used to develop desirable traits in plants and animals.
  9. One disadvantage of sexual reproduction is that organisms must grow and develop until they are mature enough to produce sexcells.
  10. Another disadvantage is that searching for a mate takes time and energy and might expose individuals to predators, diseasesor harsh environmental conditions.

6-1 Homework Check – Write the capital letter of the correct answer.

  1. diploid cellF. mitosis
  2. eggG. sexual reproduction
  3. fertilizationH.sperm
  4. haploid cellI. variations
  5. meiosisJ.zygote

G1. production of an offspring through the combination of sperm and egg

A2. body cell or zygote, which has pairs of chromosomes?

H3. male sex cell

C4. joining of egg and sperm

J5. an advantage of sexual reproduction

B6. female sex cell

D7. male or female sex cell that has only one chromosome from each pair

E8. process by which one diploid cell divides into four haploid cells

F9. Process by which one diploid cell divides into two identical cells

I10. the cell formed by fertilization

6-2 Homework Check

  1. Prokaryotic cell division is called FISSION
  2. An amoeba reproduces through MITOSIS

Asexual Reproduction 6-2

  1. What is asexual reproduction?
  2. In asexualreproduction, one parent organism produces offspring without meiosis and fertilization.
  3. Because the offspring of asexual reproduction inherit all their DNA from one parent, they are genetically identicalto each other and their parent.
  4. Types of Asexual Reproduction
  5. Cell division in prokaryotes is known as fission
  6. During fission, DNA is copiedand the cell splits to form two identical offspring. The original cell no longer exists.
  7. Many unicellular eukaryotessuch as an amoeba or bacteriareproduce by mitotic cell division. In this type of asexual reproduction, an organism forms two offspring through mitosis and cell division.
  8. In buddinga new organism grows on the body of its parent by mitosis and cell division. When the bud becomes largeenough, it can break from the parent and live on its own.
  9. Regenerationoccurs when an offspring grows from a piece of its parent.
  10. Sea stars, sea urchins, sea cucumbers, and planarians can reproducethrough regeneration.
  11. Many animals can regeneratedamaged or lost body parts. This is not reproduction; new individualsare not produced.
  12. Vegetativereproduction is a form of asexual reproduction in which offspring grow from a part of a parent plant.
  13. cloningis a type of asexual reproduction developed by scientists and performed in laboratories. It produces identicalindividuals from a cell or from a cluster of cells taken from a multicellular organism.
  14. Using a cloning method called tissue culture, plant growers and scientists can use a meristem to make a copy of a plant with desirable traits.
  15. Because all of a clone’s chromosomescome from one parent, the clone is a genetic copy of its parent.
  16. Asexual reproduction enables organisms to reproduce without a(n) mate.
  17. Asexual reproduction also enables some organisms to rapidly produce a large number ofoffspring.
  18. Asexual reproduction produces offspring that are genetically identical to each other and to their parent. This results in minimal genetic variationwithin a population.
  19. Genetic variation is important because it can give organisms a better chance of survivingif the environment changes.
  20. Genetic changes, called mutationscan occur and then be passed to offspring; this can affect the offspring’s ability to survive.

Page 9 Notes

Advantages of Sexual Reproduction

  • genetic variation – slight variations may help if there are environmental changes, such as resistance to disease, drought, and cold
  • selective breeding – man made; choosing to plant with the seeds of the desired traits. Also relates to breeding traits in animals

Disadvantages of Sexual Reproduction

  • longer time and more energy is expended
  • searching for mates could be dangerous
  • can only reproduce during certain times

Advantages of Asexual Reproduction

  • enables organisms to reproduce without a mate
  • enables organisms to rapidly produce a large number of offspring

Disadvantages of Asexual Reproduction

  • produces offspring that are genetically identical to their parent (little genetic variation)
  • harmful genetic mutations can occur