Name __________________________________ Date _________________ Period _______
(What Gregor Mendel Didn't Know)
Introduction: Gregor Mendel made some remarkable discoveries about how traits are passed from
parents to their offspring. However, Mendel couldn't explain what was physically happening within
cells to pass these traits on because he didn't know anything about chromosomes. This wasn't
Mendel's fault: microscopes weren't good enough when he was alive to see chromosomes. No one knew
then that DNA was the molecule that contained genes and that it was contained inside chromosomes
Now that we know that genes are coded in DNA inside chromosomes, we can explain why genes
do all the things Mendel said they did hundreds of years ago. By understanding what happens to the
chromosomes when sperm and eggs are formed, we can understand why children look a little bit like
their parents but are not identical to them.
During this simulation, you will only be looking at what happens to the chromosomes during
meiosis; the centrioles, nucleolus, and nuclear membrane also undergo important changes (just like
they do in mitosis), but for the sake of simplicity, they will not be looked at in this activity. When you
draw pictures, make sure you color code and size code them; this will make it easier to understand
what is happening.
**YOU MUST COLOR CODE
ALL YOUR PICTURES AND DRAW
THE SIZES OF CHROMOSOMES
CORRECTLY!!! ** Ex)
1. Set up your original cell: In the center of your table put one short green pipe cleaner and one long green pipe
cleaner; one short red pipe cleaner and one long red pipe cleaner. The red pipe cleaners came from this cell's Mom;
the green pipe cleaners came from Dad.
The total number of chromosomes of this cell = _________
How many homologous pairs does this cell have = _________
2. During Interphase the DNA replicates and the chromosomes double. Put the other pipe cleaners next to the ones
already in your "cell" to show the doubled chromosomes. Twist them together to show the centromere.
Draw your chromosomes here:
COLOR CODE!! You need to
use two different colors,
(they do not have to be red
3. During Prophase I, the homologous pairs line up next to each other. They usually get so close that parts of them
wrap around each other and exchange pieces (called crossing over). Put the "homologous" pipe cleaners next to
each other, and wrap their tips around each other.
Draw your chromosomes here:
label the homologous pairs and
CIRCLE where crossing over is
happening COLOR CODE!!
4. In Metaphase I, the chromosomes line up in the middle of the cell. They line up differently than they do in mitosis,
though. If you were to draw an imaginary line down the middle of the cell, one doubled chromosome of each
homologous pair would be on each side of the line. CHECK THIS ARRANGEMENT WITH YOUR
TEACHER BEFORE CONTINUING!
There are 2 ways in which your chromosomes can be arranged. Draw both ways but continue on with
only one of the two arrangements. Also, draw a dotted line between the homologous pairs to illustrate
the metaphase “plate”. COLOR CODE!!
First Arrangement Second Arrangement
5. In Anaphase I, chromosomes move towards opposite sides of the cell, but the doubled chromosomes stay attached at
How is this different from Anaphase in mitosis?
Will the two new cells be genetically identical to one another? ___________
WHY? EXPLAIN below
6. In Telophase I, the chromosomes are
at opposite ends of the cell. Just after
Telophase I the cell divides.
Draw your two new cells:
** How many chromosomes does each new cell have? __________, ( or _______ pairs of sister chromatids).
7. The two new cells go through the second stage of meiosis, which is just like mitosis. Do the chromosomes
double again before the second division? __________ EXPLAIN YOUR ANSWER BELOW.
8. Draw pictures of what the
four new cells would look like at
the end of the second division
of meiosis. COLOR CODE!!
** How many chromosomes does each cell have? _____________
1. One of the main purposes of meiosis is to cut the chromosome number in half.
a. Why does the chromosome number need to be cut in half?
b. During which phase of meiosis does the chromosome number get halved? ____________________
(Consider that a "doubled" chromosome does not really count as two chromosomes because it is just a
duplicate of the first with all the same genes. )
2. In human cells, the diploid number of chromosomes is 46. How many chromosomes would be in a human sperm