| Cell Reproduction |
| Biology Genetics Day 10 Cell Reproduction Science Probe 10, Chapter 16, pp. 356-372 PLO addressed: �compare and contrast sexual and asexual reproduction� �compare the changes that occur during the stages of a cell�s development� Materials: See attached overheads/handouts Teacher�s Background Info: Asexual single-celled organisms and somatic cells of multi-cellular organisms divide by mitosis. In this process, all genetic information in the parent cell nucleus is duplicated and then partitioned into daughter cells. Estimated Time for Activity: 55 min. Content: Teacher presentation of mitosis (asexual reproduction) and meiosis (+ relate to sexual reproduction). This lesson will be a combination of lecture and class discussion. Teacher may begin by introducing the idea of reproduction: making more copies of something. What we normally associate with copying (e.g. photocopying) is very similar to asexual reproduction. This is because a copy of something is exactly the same as the original. In asexual reproduction, a �parent� cell produces two identical �offspring� cells by splitting in half. Sexual reproduction can be introduced at this point, using an analogy to the visual comic trick of combining the features of two people into one face (� la Conan O�Brien�s �If They Mated�). The fact that there are two parents rather than one should be emphasized as a difference from asexual reproduction. It should be mentioned at this point that the characteristics of the two parents are not simply averaged, but interact in a complex way. Asexual reproduction can now be returned to in more detail. Diagrams on an overhead and on handouts (see attached sheet) should be used as the teacher summarizes mitosis. Students should be asked to take down key points on the handout and to ask any questions they have. |
| The teacher may simplify mitosis even more than is done here if s/he sees fit. The main point to mention is that the chromosomes change in structure during mitosis. During Interphase, the cell is not dividing and the chromosomes are spread out and not visible under the microscope. The start of mitosis is when the chromosomes are duplicated and condensed, so that pairs of sister chromatids are visible; this is called Prophase. In order that the two daughter cells get the same amount of DNA, the chromosomes are lined up across the cell in Metaphase. In Anaphase, the cell pulls the sister chromatids to either side so that the exact same chromosomes are found in each end of the cell. A cell membrane forms in Telophase to separate the daughter cells. The cell goes back to Interphase and the chromosomes are again invisible. As a way of deepening this lesson and of introducing genetics, the teacher begin asking some questions relating to genetics. Teacher explains that chromosomes contain the genetic information of the cell in the form of genes, and that genes are what determine the characteristics of the cell. Then s/he asks questions like: If a single-celled organism was adapted to a certain environment (cool and moist) and reproduced over and over to form 64 daughter cells, which of these cells would be best adapted to a different environment (warm and dry)? If one gene of a cell was changed (mutated), how many of its daughter cells would be affected by the change? Can anyone think of some problems with this? Closure: Sexual reproduction should be brought up again here, as it relates directly to the above questions. Teacher mentions that sexual reproduction will be the topic next lesson. |