The Chromosomes of a Nerf: an Imaginary Animal

The Chromosomes of a Furnf: An Imaginary Animal

ANSWER QUESTIONS SHOWN IN BOLD!

Introduction

By now, you should probably know that chromosomes contain genetic information (they are made up of (a)______) and that every person has (b)______pairs of chromosomes containing exactly the same genetic information in every cell in his/her body (except the sex cells). But have you ever seen a chromosome? Have you ever seen mitosis or meiosis as it was happening? Probably not because chromosomes are too small to see with the naked eye. One way that scientists try to understand processes that are too small (or too big) to see is to build simple models and to use them to try to understand how things work. In this lab, you will use colored paper to make models of the chromosomes in a cell of your Furnf that has a total of 6 chromosomes per cell (2n=6). You will use these models to help you answer questions throughout the lab.

Procedures

Fold the blue sheet in half lengthwise (along the solid line).
Keeping the sheet folded, cut on the dotted lines-Keep the 3 folded pieces of paper that have a shape that looks like this <.
Repeat steps 1 and 2 with the pink sheet of paper.
You should end up with 6 pieces of paper that have the < shape. For now, keep them folded.
Write 1 group members name on the back/bottom of each chromosome.
Number each of your chromosomes from 1 to 3 (make sure you write the same number on each chromatid).
These are the chromosomes in a normal Furnf cell. (b.1) Please make a labeled drawing of your chromosomes below. Be sure to consider the size, shape, number, and colors of the chromatids.

Interphase

With your paper models folded, you are looking at a chromatid.

(c) During what part of Interphase does replication of the chromatids take place? ______

Unfold all of your chromosomes so that the models looks like an X. The unfolding represents the replication of the DNA in the chromatid. Notice the 2 sides of the X are identical and are called (d)______.

(e) What structure holds the 2 chromatids of a chromosome together? ______

Put this structure onto your chromosomes by drawing a circle in the center of each chromosome.

Modeling Mitosis

You should all be quite familiar with the process of mitosis, which is the division of the (f)______. You will notice as you begin to perform mitosis, that some very important functions will be ignored like the (g)______whose job is to connect to the chromosomes and pull them to opposite sides of the cell.

Attempt to model mitosis by moving the chromosomes around on the table to represent each of the 4 phases, (h) ______and ______. You will need scissors to do the 3rd step of mitosis.
Draw each of these 4 phases below as is shown by your Furnf (6 total chromosomes). Remember to label each drawing.

The process of mitosis begins with one cell, and finishes with (j) ______ identical cells.

(k) In ONE of your new cells following mitosis, how many chromatids of each color are there? ______

(l) In ONE of your new cells following mitosis, how many chromatids of each size are there? ______

Use a piece of tape to rejoin your identical chromatids once again, making chromosomes.

Modeling Meiosis

Before we can begin, let’s think about sex. (m) First of all, why do you think some of the chromosomes are blue and some are pink?

Furnfs are animals and each Furnf has a mother and a father. When Furnf males mate with Furnf females, a sperm cell from the father joins an egg cell from the mother. The haploid sperm cell from the father and the haploid egg from the mother both contain DNA in the form of chromosomes. They join together and their chromosomes mix making an embryo cell called a zygote that is now (n) ______, which will eventually become a baby Furnf (after a great deal of mitosis!). The baby Furnf has to also go through meiosis to make its own sex cells (in males, not until puberty, in females before they’re born). In our model, the chromosomes that are blue have come from the father Furnf, while the chromosomes that are pink have come from the mother Furnf.

Using a pencil or pen, draw a line on the large blue chromosome to represent a gene and label it with the letter B. Remember these 2 chromatids are identical!
Draw a line on the large pink chromosome in the same place, but label this gene b. Again, remember these 2 chromatids are identical!
(o) Different variations of the same gene are called ______.

Meiosis I (you will need scissors again for parts of Meiosis)

(p) For each phase of meiosis, draw what your chromosomes look like in the boxes provided.

Prophase I

During this phase, homologous

chromosomes line up together.

Metaphase I:

Notice that the blue and the pink chromosomes do not

always have to be on the same side of the equator (middle line)

when the pairs move to the center.

This is called (q)______.

Anaphase I:Telophase I:

Meiosis II

Prophase II:Metaphase II:

Anaphase II: Telophase II:

(r) At the end of Telophase II, how many new cells have been formed? ______

Re-tape your chromatids back together again.
Repeat Meiosis again, but this time switch the large chromosomes to the opposite sides of the equator (middle line). This means, if your Large blue chromosome was on the left side of the cell before, this time put it on the right side of the cell in Metaphase I.
(s) What has this change in the placement of the large blue and pink chromosomes during Metaphase I done to the sperm in the final result?

Additional Questions

(t) During which phase of Meiosis can crossing over occur? ______

(u) How many chromatids are present in each cell at the end of meiosis? ______

(v) Are these final cells made at the end of meiosis haploid or diploid? ______

(w) Can you come up with an analogy to represent the idea behind independent assortment?

(x) What is Mendel’s Law of Random Segregation? Explain in your own words….

(y) Which stage of Meiosis (I or II) is most similar to mitosis? ______

Draw a picture of your Furnf below. We are all very curious to know what Furnfs really look like!