Lab: Meiosis

INTRODUCTION
      All plants and animals inherited their traits from both their parents. These traits are passed
from the parents to the offspring through chromosomes located in the "sex cells" of the parents. What is unique about these sex cells, both sperm and egg, is that they contain only 1/2 the
number of chromosomes as all other cells in the body.
      Meiosis is the study of why, and how, an organism would make specialized sex cells. To understand why organisms undergo meiosis it must first be understood that each parent must
only give its offspring 1/2 of its chromosomes. To better explain this let's consider humans. A
normal human has 46 chromosomes, 23 of which came from the mother, and 23 from the
father. All body cells will have these same 46 chromosomes. When a body cell needs to
reproduce it will simply make a copy of each chromosomes producing a total of 92
chromosomes, and then divides them equally between two daughter cells. This process, called mitosis, maintains the normal number of 46 chromosomes in each cell. To produce a new
human, however two cells, called sperm and egg, must join without immediately dividing
afterwards. If these sperm and eggs each contain the normal 46 chromosomes, then the new offspring would have 92 chromosomes in each cell, and would quickly die. To prevent this
each parent produces sperm and egg containing only 23 chromosomes, so that when they join
a zygote with the normal 46 chromosomes is produced. Meiosis, then, is the process by which parent produce "sex cells with 1/2 the normal number of chromosomes".
      The following diagram shows the chromosomes found in the nucleus of an imaginary
organism. This organism contains 4 chromosomes, arranged into 2 homologous pairs. Use
this diagram, and the "cutouts" provided in the back of this lab, to imitate the process of
meiosis in the diagram labelled Circle #1.

PROCEDURE

PART I : Steps of Meiosis
      Use the circle provided on the following page to show how the chromosomes would
appear in ALL phases of Meiosis. Each time you have the chromosomes arranged for a phase,
SHOW IT to the teacher. Once correct indicate this with an “OK” in the appropriate box in
the Data Sheet. After each step is arranged, answer the questions on the Data Sheet BEFORE taking the chromosomes apart to make the next step.

PART II : Nondisjunction
      Klinefelters Syndrome and Turner’s Syndrome are two common examples of nondisjunction involving the sex chromosomes. Review the cause of each of these disorders and select one to demonstrate next. Use Diagram #2, and the “cutouts” provided in the back of this lab, to imitate
one example of nondisjunction in either a female or a male. Show your example of nondisjunction through all the phases of Meiosis. Again use the diagram labelled Circle #1. Each time you have
the chromosomes arranged for a phase, SHOW IT to the teacher. Once correct indicate this
with an “OK” in the appropriate box in the Data Sheet. After each step is arranged, answer the
questions on the Data Sheet BEFORE taking the chromosomes apart to make the next step.

CUT-OUTS

For PART I

For PART II