Models of the chromosomes of the imaginary Leksak bird can be found at the end of this activity.  The dark bands on these chromosome models are genes.  Most cells in this bird’s body contain the same number and type of chromosomes.  The importance of genes to all living things, and to the Leksak bird as well, is that they control all inherited traits.  Chromosomes are important because they are the carriers of these genes.

 Strategy

You will cut out and pair chromosome models of the Leksak bird.

You will determine what type of change occurs in the number of chromosomes when a cell divides by mitosis and meiosis.

 Materials

Scissors

 Procedure/Data and Observations

1.       Cut out each chromosome model in Figure 1.

2.       Fold each paper model in half along dotted lines.

3.       Match in pairs as many chromosome models as possible.  A chromosome pair must match in length as well as in number and location of genes.  The lines on the chromosome models represent genes.

4.       Answer question 1-4 in Questions and Conclusions before proceeding further.

5.       Cut each chromosome model in half along the dotted line.  Make two piles of chromosome halves.  Put on half of each chromosome in one pile and the other half in the second pile.

6.       Compare the chromosomes in the first pile with those in the second pile.

7.       Before proceeding, answer questions 5 and 6 in Questions and Conclusions.

 

A process of cell division called mitosis occurs in most living things.  During mitosis, one cell divides to produce two cells.  The cutting of each chromosome model and separating them into two piles is similar to what happens in a living cell.  The two piles of chromosome models represent two new cells.  (Each chromosome duplicates itself and the two halves then separate.)

1.       Place all identical chromosome models together in separate groups.  You should have six groups of models.

2.       Take a group of matched chromosomes and separate them in6to four piles.  Take a second group of matched chromosomes and place on chromosome from the group into each of the four piles.

3.       Continue this sorting until all chromosome models, including the unmatched chromosomes models, have been separated into the four piles.  Each pile of chromosome models represents a sex cell.

 

A process of cell division called meiosis occurs in most living things.  During meiosis, one cell divides to produce four cells.  Each new cell produced by this process is called a sex cell (egg or sperm cell).

 

Questions

 

1.       How many chromosome scan be found in each of the Leksak bird’s cells?

2.       How many matched pairs of chromosomes are there in each cell?

3.       How many unmatched chromosomes are there in each cell?

4.       Do the genes on each matched pair of chromosomes also match?

5.       After separating the chromosome model halves into two piles, how many models are found in each pile?

6.       How many chromosomes are found in Leksak sex cells?

7.       Do any chromosomes match one another in a sex cell?

8.       Male Leksak birds have six matched pairs of chromosomes and two unmatched chromosomes.  Female Leksak birds have seven matched pairs of chromosomes.  Were the chromosomes in our bird taken from a male or female?

9.       Are all cells produced by mitosis exactly alike, chromosome for chromosome? Gene for gene?  Explain why.

10.   How does the number of chromosomes in sex cells compare to the number of chromosomes in cells  formed during mitosis?

11.   Explain two ways in which sex cells differ from all other cells.

Conclusion: What did you learn about mitosis and meiosis? Compare and contrast each type of cell division. What cells reproduce by mitosis? By meiosis? What is the importance of each process?