Lab Example: Constructing and Thinking about Chromosomes

Introduction:

In this lab, you will complete the mitosis and meiosis simulations. Both of these processes are part of the stage of cell division called karyokinesis. Karyokinesis is just one phase of cell division and is defined as the division (or reproduction) of the genetic material, or we could say the division (reproduction) of the nucleus. The second phase of cell division is called cytokinesis and involves the division of the cytoplasm.

In most multicellular organisms, mitosis dominates as the most abundant nuclear division process. It is essentially part of a copying process whereby tissue cells are replaced or regenerated, for instance, in the replacement or growth of cardiac muscle, neurons in the brain, or skin cells.

Meiosis is the nuclear division (reproduction) process only found in gametes or the sex cells, which are the egg and sperm cells of sexually reproducing organisms. It is also a reducing process at thesame time that it is a reproduction process. What does this mean? Its a reducing process since egg and sperm cells are created with half the number of chromosomes. Why does this occur? This reduction occurs so that when the egg and sperm fuse to make the new individual, the original number of chromosomes is restored.

Also during meiosis, two processes which lead to genetic variability occur: crossing over of chromosomes (which we explored briefly in Chromosome Lab Activity 1) and separation of homologous pairs of chromosomes. The overall process of meiosis begins with a single diploid pre-gamete cell, which in humans contains 46 chromosomes, and the end result is four haploid gamete cells, each containing 23 chromosomes.

To simulate meiosis in our lab,you will use 2chromosomes (1yellow and 1red) to represent the diploid conditionand 1chromosome to represent the haploid condition. At the end of meiosis, the result will be4haploid cells containing only 1chromosome. To help you visualize this, look at thesketch below (also view Figure 3.3 in the Lewis text). You will see a single diploid cell with 2chromosomes. Crossing over will occur before the first division (meiosis I), and then there is a second cell division (meiosis II) resulting in 4haploid cells. In the third activity, you will be looking at chromosome misregulation or nondisjunction. This occurs when chromosomes fail to separate from one another. It will be helpful to look at Figure 13.12 in the Lewis text.

In this lab, you will be constructing chromosomes from a kit from Carolina Biologicals. Follow the instructions as stated for construction of the chromosomes, then answer a series of short answer questions and write a short essay (see assessment below).

Supplies needed

Meiosis and Mitosis Chromosome Simulation Kit, Carolina Biological Supply

String, short rope, or masking tape to make outline of nucleus

Phone/tablet/computer camera, or digital camera

Reading:

Lewis text:chs. 23 (Sections 2.1, 2.3, 3.3 [especially Figure 3.3]), and ch. 13, pp. 245246 (especially Figure 13.12)

Carolina Distance Learning Investigation Manual: Mitosis and Meiosis: Chromosome Simulation, pp. 1124

Assessment:

1. Nondisjunction.

2. Meiosis 1.

3. Synapsis.

4. Eukaryotic cells.

5. Homologous pairs.

6. Haploid cells.

7. Gametes.

8. 23.

9. Cross over.

10. Disjunction.

Down syndrome (trisomy 21) is a genetic disorder brought about by abnormal or extra chromosomes altering the manner in which the body and brain develop. It is the primary genetic chromosomal disorder of learning disabilities among children. Often, it creates other medical abnormalities among them gastrointestinal and heart disorders. Chances of getting the disorder are; if a mother is older when getting pregnant and having a sister or brother with Down syndrome. Symptoms of Down syndrome include; short arms, neck, and legs, below average intelligence, distinctive facial features like small ears, small mouth, a flat face, and slanting eyes. Most kids with the disorder are as well born with heart, breathing, intestine, or ear problems. Diagnosis of Down syndrome is usually made during pregnancy through screening and diagnostic tests (Dierssen & Torre, 2012). Children living with Downs syndrome can be assisted in different ways to lead fulfilling and healthy lives as noted in Luke 18:16 Let the children come unto me, for to such belongs the kingdom of God. Through good care, individuals living with Down syndrome are in a position to leave their homes, work, and lead independent lives.

References

Dierssen, M., & Torre, R. (2012). Down syndrome: From understanding the neurobiology to therapy. Amsterdam: Elsevier.

Yong, A. (2007). Theology and Down syndrome: Reimagining disability in late modernity. Waco, Tex: Baylor University Press.

MEIOSIS DIAGRAM

diploid condition = two chromosomes