Biology
Name ______________________________
Computer Lab Activity
MODS___________ Date _____________
Meiosis
All students will need a notebook for today’s visit.
You should record all information in your notebooks, when directed.
Do not PRINT-OUT information; it must be HAND-WRITTEN.
Instructions:
1. Click on the Netscape / Internet Explorer / Firefox / Safari icon, to sign on to the Internet.
2. Click on the “empty rectangular area” at the top of your screen.
3. Carefully type in http://biology.clc.uc.edu/courses/bio104/meiosis.htm and hit return (enter).
Part II: Meiosis
Copy the following into your notebook:
Meiosis
1. In _______________ _______________, two parents give rise to an offspring with a unique gene
_______________ from both of them -- each parent gives _______________ of his/her genes to the
_______________. A _______________ is a discrete unit of information on the ______________ that
codes for one protein, perhaps one of the many enzymes needed by our cells (and
_______________).
2. _______________ cells (which are regular _______________ cells) have two sets of
chromosomes; one set from _______________ _______________.
a. For example, in humans one “1/2” set = _______________ chromosomes, so our somatic
cells
have
_______________
chromosomes
arranged
in
_______________
______________.
b. The two chromosomes in each pair are referred to as being chromosomes, so we could say
that humans have _______________ pairs of _______________ chromosomes.
c. The two chromosomes of each pair carry genes for the same trait (for example,
_______________ _______________ ) at the same _______________, but not necessarily the
same form of that _______________ (for example, _______________ vs. _______________
eyes).
3. An important exception to this is the sex chromosomes, the _________________ and
_________________ _______________.
a. Although these chromosomes pair with each other, they are not the _______________
_______________. The X-chromosome is _______________ and has genes for many
_________________ with no match on the Y-chromosome.
1
b. A person with XX would be _______________ and someone with XY would be
_______________.
c. All the other chromosomes are called _______________.
4. Somatic cells have two sets of _______________ (2 x 22) chromosomes, and one pair of
_______________ _______________.
a. They are called _______________ or 2n cells.
b. Thus, humans would have (22 pr + 1 pr = 23 pr) or 44 + XX (female) or 44 + XY (male)
_______________.
5. Gametes or _______________ ________________ (eggs from _______________ and sperm from
_______________ ) have one chromosome from each autosome _______________ and one sex
chromosome (one set of chromosomes), thus are called haploid or _______________.
a. Eggs and sperm have ½ of each pair (so they can unite during fertilization to make
complete pairs (or a total set of 23 pr).
b. Human eggs would have _______________ chromosomes, and sperm would have
_______________ or _______________ chromosomes.
6. Meiosis is a _______________ type of cell division that produces _______________ with half as
many chromosomes.
a. The opposite process would be syngamy or _______________, which is the union of the
_______________ and _______________ to restore the 2n number.
b. This results in a _______________, the first cell formed by _______________, a completely
new and different _______________ with unique genetic information _______________
from either ___________.
c. The zygote divides and grows to form an _______________ which develops into a young
organism, then an _______________.
7. The steps in meiosis are _______________ to mitosis and even have the same names.
a. However, there is a significant difference in how the chromosomes _______________
_______________ initially.
b. In mitosis, chromosomes line up _______________; in meiosis, the homologous pairs line up
_______________ _______________ each other.
c. In meiosis, this pairing process is called _______________, and the resulting homologous
pair is called a _______________ in reference to the two chromosomes or a _______________
in reference to the four _______________ chromatids involved.
8. Interphase is the same in both _______________ and _______________, but in meiosis, it is
followed by _______________ cell divisions. These two division processes are referred to as
Meiosis _______________ and Meiosis _______________, and result in a total of four
_______________ cells, each with a _______________ chromosome number.
2
Meiosis I
a. In prophase I, the homologous chromosomes come together and match up
(_______________) in pairs(tetrads or _______________). A baby girl is born with all the
precursor _______________ ____________ she will ever have in a sort-of “suspended
animation” until ____________.
b. In metaphase I, the bivalents _______________ _______________, not individual
_______________, so there’s a _______________ chance of which chromosome of each pair
faces which pole of the cell - or goes to which daughter cell.
c. In anaphase I, the homologous chromosomes _______________, and one of each pair
travels to each of the two poles of the cell, reducing the chromosome number from
_______________ to _______________. (Sister _______________ stay together.)
d. During telophase I, two ________________ _______________ are formed. These usually
go immediately into the second cell ________________ (meiosis II) to separate the sister
chromatids.
Meiosis II
a. Like mitosis, the sister chromatids are ________________.
This results in
________________daughter cells, each with an ____________ chromosome number.
b. Fertilization triggers ________________, and then the sperm nucleus ____________ with the
resulting egg nucleus.
c. In human females, division of the cytoplasm is _______________ _______________. This
provides a way of keeping as much ________________ as possible with the future egg/zygote.
d. Rather than equal-sized gametes, one big egg and three smaller ________________
_______________ are formed.
Interestingly, because the homologous pairs line up during Metaphase I, there is a 50:50 chance of which one of each pair
will go to each of the poles of the cell (like flipping a coin, where you can get either heads or tails). Therefore, in humans
with 23 pairs of chromosomes, a gamete (egg or sperm) could have 223 or 8,388,604 possible combinations of
chromosomes from that parent. Any couple could have 223 ¥ 223 or 70,368,744,177,644 (70 trillion) different possible
children, based just on the number of chromosomes, not considering the actual genes on those chromosomes. The
chance of two siblings being exactly identical would be 1 in 70 trillion. In addition, something called crossingover, in
which the two homologous chromosomes of a pair exchange equal segments during synapsis in Meiosis I, can add further
variation to an individual’s genetic make-up.
3