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Meiosis Notes- 11.4
As we learned, body cells, also known as somatic cells are created by the process known as
___________________. Mitosis (followed by cytokinesis) results in two __________________ cells that are
identical. Mitosis contains 4 distinct phases that allow for __________________ and repair in the body.
Human somatic (_______________) cells contain ___________ chromosomes, which means your lung, heart,
etc. cells all contain 46 chromosomes. This is called the __________________ number. "Di" means
_____________ and "n" stands for the number of chromosomes. Diploid is written as _______.
Sex cells are referred to as _________________ and use the process called _________________ to reproduce.
There are two types of gametes....
1. Males make __________________(_____).
2. Females make _________________(______).
If the diploid number (2n) consists of 46 chromosomes, then what do you think the haploid number (1n) is?
Let's review....
____________________ cell (body cells)
2n=46 chromosomes
_______________________ (egg and sperm)
1n=23 chromosomes
n= chromosome number
1n = haploid
2n = diploid
Organism
Mosquito
Cat
HUMAN
Chimpanzee
Dog
Tomato
Haploid
number(n)
3
19
24
39
Diploid
number(2n)
6
38
46
48
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Sexual Reproduction
The union of a single sperm and a single egg is called __________________________. Before fertilization can
happen, there must be ____________ separate sets of genetic information; one set from mom and one set from
dad. Therefore, the genetic information must be _________________, which happens by the process of
meiosis. Meiosis produces sperm and eggs that have _______________ the amount of DNA/number of
chromosomes as the diploid cell.
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Let's take a look at an egg and a sperm.


Sperm is made by ______________ (XY) by the type of meiosis known as spermatogenesis.
Eggs are made by females (XX) by the type of meiosis known as _____________________.

Spermatogenesis creates ______________ haploid sperm (23 chromosomes). This occurs in the gonads
named the _____________________.
Oogenesis creates ________________ haploid egg (23 chromosomes). This occurs in the gonads named
the __________________________.

___________________________ is when an egg and sperm fuse. Remember, the egg and sperm each contain
___________ chromosomes (one from mom (1n) and one from dad (1n)). 23 + 23 = ________(2n). This union
creates a _______________________.
The ___________________ (2n) begins to divide by the process of __________________. Remember, meiosis
creates the gametes, but once they fuse and create the zygote, somatic cells begin to divide by mitosis. This
division will form a solid ball of cells referred to as a ________________________, then an embryo, and
eventually, a baby.
Let's look at this process a little more in depth.
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The solid ball of cells that forms after the first few divisions is called a morula. Once the ball of cells is no
longer solid, but becomes hollow in the inside, it is called a ______________________. The ball of cells start
to push inward and is then called a ________________________. From zygote ----> morula ---> blastula, all of
the cells were ________________ and the structure stayed the same size (there was no
__________________________ of interphase). Once the ball formed a gastrula, the cells begin the process
called differentiation, which is when cells start to become ___________________________. This means that
they become different types of cells, such as liver cells, bone cells, heart cells, etc.
When does an embryo become a fetus?
 The embryo becomes a fetus at approximately _______ weeks. At this point, some of the organs are
actually starting to function; kidneys, _________________, brain, and ______________.
A Quick Look at Stem Cells
A stem cell is an ______differentiated cells. This means that these cells do not yet have a specific
______________ to do. Some stem cells are taken very early in development (ex: from a zygote or an embryo)
while others can be taken from adults (ex: bone marrow). We will explore this topic in more detail when we get
into our biotechnology chapter.
How are twins created?
 Fraternal twins are created when ________ different eggs are fertilized by __________ different sperm.
 Identical twins are created when ________ sperm fertilizes _________ egg, but the morula (ball of cells)
splits into 2!
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The Specifics of Meiosis
Meiosis consists of __________ divisions. We call these Meiosis _____ and Meiosis _________. Again,
meiosis results in _______ DIFFERENT haploid cells, containing 1/2 the amount of genetic material. This is
why you have some similar features to your parents, but are not exact replicas!
Q: What do you call the 2 matching X's next to each other?
 Homologous __________________________/pairs OR
homologues.
Q: Do the homologous pairs (homologues) separate from each
other during meiosis I or meiosis II?
 Meiosis _______.
Q: When do the sister chromatids separate?
 During meiosis ____________.
.
Crossing Over, what's that?
Crossing over creates ___________________ diversity and allows for variation (differences) among organisms!
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Interphase
Consists of _______, S, and _______. The
cell grows and makes more organelles.
DNA is copied during the ________
phase. DNA is in the _______________
form called chromatin.
Meiosis I
Prophase I
The nuclear membrane and nucleolus
disappears, spindle _____________, DNA
condenses, homologous
chromosomes/homologues find the
matching _________________ and form a
group of ________ called a tetrad. This is
when crossing over occurs.
Metaphase I
Homologous chromosomes meet at the
_____________ of the cell and the spindle
is now complete.
Anaphase I
Homologous chromosomes separate and
travel towards the opposite ____________
of the cell.
Telophase I
The nuclear membrane and nucleolus
reappear, spindle breaks down, ________
loosens into chromatin, and the cell
membrane pinches inward. Cytokinesis
occurs and _______different cells have
formed.
Meiosis II
Prophase II
Nuclear membrane and nucleolus
disappear, spindle forms, DNA condenses.
Metaphase II
The _______________ chromatids meet at
the middle of cell and the spindle is now
complete.
Anaphase II
The sister chromatids separate and travel
towards the opposite poles of the cell.
Telophase II
Nuclear membrane and nucleolus
reappear, spindles break down, DNA
_____________ into chromatin, cell
membranes pinch inward. Cytokinesis
occurs and _______ different haploid cells
have formed.
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Review
Q: When do the matching X's/homologous pairs (homologues) find each other? What do they
form?
 During __________________________. They form a _________________.
Q: How many homologous pairs do humans have?
Q: In what phase of meiosis does crossing-over occur? What does crossing-over create?
 During ____________________________ and it creates _________________ diversity or
variation.
Q: What separates during anaphase I?
 __________________________ pairs
Q: What separates during anaphase II?
 _______________________ chromatids
Q: Is there an interphase during meiosis I and meiosis II?
Q: Which process allows somatic cells to divide? Is this sexual or asexual reproduction?
 ______________________________ and it is _________________ reproduction.
Q: Which process creates gametes? What are the gametes called? Is this sexual or asexual
reproduction?
 _____________________________. They are referred to ____________ and sperm.
Meiosis is ___________________ reproduction.
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