Download What is Meiosis? - Manhasset Public Schools

Name:
Aim 35: What is Meiosis?
I.
Date:
What is Meiosis?
What is Meiosis?
1. The process in which __________________ (______________) are produced.
2. Males produce ______________ cells and females produce ___________ cells through meiosis
Which organisms
undergo Meiosis?
Where does
Meiosis occur?
____________________ reproducing organisms (humans, animals etc). Egg and sperm cells must
be created through meiosis before sexual reproduction can occur.
1. Sperm are produced in the ________________ of males (produced continuously throughout life)
2. Eggs are produced in the ________________ of females (all produced before the female is born)
1. Meiosis begins with _____________________________ with a _____________________ set
What does
Meiosis produce?
of chromosomes (diploid cell = 2 of every chromosome)
•
Ex: In humans, meiosis begins with a body cell with 46 chromosomes (23 pairs)
2. Meiosis ends with ________________________________ with a ______________ set of
chromosomes (haploid cell = 1 of every chromosomes)
•
Ex: in humans, meiosis ends with a sperm or egg cell with 23 chromosomes (no pairs)
What is Meiosis
also known as?
II.
= the formation of gametes (egg and sperm) through meiosis
Chromosomes and Chromosome Number
A) Chromosome Number
To have a complete set of chromosomes.
A cell that has 2 of each chromosome in a
pair (1 form each parent)
To have a half set of chromosomes. A cell
that has 1 of each chromosome not in a
pair.
Body cells (liver cell, eye cell, heart
cell, root cell of a plant etc.) Any
cell BESIDES a reproductive cell
Gametes (Egg and sperm.) ONLY
reproductive cells.
1. The human diploid number is:
2. The human haploid/monoploid number is:
3. One chromosome of each chromosome pair is from the ________________ and one is from the _____________
4. A human cheek cell has ____________ chromosomes because it is a ________________ cell.
5. A human egg cell has ______________ chromosomes because it is a ________________ cell.
6. The diploid number for an organism is 16.
How many chromosomes are in a body cell of that organism? _______.
How many chromosomes are in an egg or sperm cell of that organism? ______. So n = _______ & 2n = _______
7. Complete the chart below
# Chromosomes in body cells
Horse
Fly
Spinach
Chicken
# Chromosomes in gametes
# Chromosome pairs in body
cells
60
6
12
8
B) Homologous Chromosomes
• The chromosomes of a body cell (diploid cells) are in the form of
____________________________.
•
Therefore, in a human body cell there are ___________________ of
homologous chromosomes
o
Body cells have 23 chromosomes are from the mother and 23
chromosomes are from the father.
o
•
Egg and sperm cells have only one member of this homologous pair
Homologous Pairs or Homologous Chromosomes are similar in size/shape,
control the same ____________ and have genes for the same characteristic
III.
Phases of Meiosis: Meiosis involves 2 divisions: Meiosis I and Meiosis II
•
_________ divisions
•
_________ cells created
•
Produces _________ and ____________
•
Daughter cells are ____________________ to parent cell
•
BEGIN with ONE _______________ CELL
•
END with 4 __________________ CELLS
Interphase
*MEIOSIS I*
(1st Division)
Prophase I
1. Chromosomes replicate in one diploid body cell
2. Chromosomes cannot be seen
This is the ONLY time during meiosis that the
chromosomes replicate
3. Chromosomes from each parent pair up and form
homologous pairs
4. Crossing over occurs (homologous chromosomes exchange
genetic information, creating new gene combinations)
Metaphase I
5. Chromosome pairs line up in the middle of the cell
(Pairs have 1 chromosome from mom and 1 from dad)
Anaphase I
6. Chromosome pairs are split apart and move to opposite
ends of the cell. This is called disjunction
Telophase I &
Cytokinesis I
7. Cell tears and two daughter cells are created, each with
duplicated chromosomes
*MEIOSIS II*
(2nd Division)
Prophase II
8. The two cells each undergo the same process as mitosis
except the chromosomes DO NOT replicate again
Metaphase II
Anaphase II
Telophase II &
Cytokinesis II
9. Chromatids separate
10. The cytoplasm of each cell tears and 4 haploid sex cells are
produced, each with half the number of chromosomes as
the original body cell
11. Each cell has 1 chromosome from each pair of homologous
chromosomes. Chromosomes are NOT paired
Gamete (Sex Cell) Formation
How does
Meiosis differ
in Males and Females?
meteIV. (Sex
Cell)
Formation
Meiotic
•
Division
MALES
= creation
of sperm
animals
(including
In female
nimals
humans), the haploid
humans), gametes produced by
d gametes meiosis are called eggs
by meiosis
Diagram
sperm
• The cell divisions at the end
of meiosis I & II are uneven,
ells are
so that 1 large egg is
from one
produced along with
vision
3 other cells, called polar
which
are discarded
What is bodies,
________ viable
_______________
sperm cells
produced and not involved in
reproduction
FEMALES
= creation of eggs
•
Cytoplasm divides _________________ in each division
•
Produces ______ large viable egg cell and _____ small
nonfunctioning cells called _______________________,
which eventually disintegrate
Why are
gametes
produced
V.
A haploid sperm and a haploid egg will combine during the
process of ____________________ to create a
__________________________ (single cell) that will eventually
divide by ____________________ and grow into an organism.
Meiosis as a Source of Genetic Variation
The events that occur during meiosis do more than just divide chromosomes into smaller sets and form smaller cells.
Meiosis is responsible for much of the genetic variation among sex cells of each individual.
A) Independent Assortment: the way the different pairs __________________________ line up in relation to other
pairs during metaphase I, leading to many possible combinations in the sex cells that result.
B) Crossing Over: When the chromosome pairs (one chromosome from mom. 1 from dad) ________________
parts during prophase I.
• When they separate, genes are _________________. All 4 cells will now carry ________________
combinations of information. No two sperm cells or egg cells are alike!
• Origin of new combinations of inheritable traits in offspring & the reason why there’s ______________
within a species
•
VI.
Why does this allow a species to evolve?
Problems during Meiotic Division
•
Recall that _________________________ occurs during Anaphase I, which is when the chromosome pairs
are evenly separate.
•
If this does not properly occur, _________________________ occurs. This results in one sex cell having the
Anaphase II
Nondisjunction in Meiosis II
_____________ amount of chromosomes.
•
An example of a disorder caused by nondisjunction is _______________________. Each body cell will have
an extra chromosome
hird picture you
w the lower red
osome only has
indle fiber
ed
ourth picture it
d one gamete to
n extra chromatid
e other gamete to
sing one.
isjunction causes
metes to have the
amount of
osomes