Download MEIOSIS LIVING ORGANISMS 2 types of cells: CHROMOSOME

3/25/2013
LIVING ORGANISMS

2 types of cells:

Autosomal (body) cells have 2 copies of every gene

Gametes (sex) cells have 1 copy of every gene
MEIOSIS
Genetics Unit
CHROMOSOME NUMBER

Autosomal (body) cells

Gametes (sex) cells

Humans 46
Sperm & Egg cells
Female XX
 Male XY


Willie Shoemaker, Wilt Chamberlain
~taken by Annie Liebowitz
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SEXUAL REPRODUCTION
WHAT IS INHERITED?

Sexual reproduction provides variation due to the
shuffling and recombination of alleles during
meiosis and fertilization
 99.99% of our DNA is the same
 MEIOSIS is what makes us different!

WHY MEIOSIS?
3/20/13

Cell division to make gametes, or sex cells
Sperm in males
 Eggs in females


Why would it be
different than Mitosis?
Diploid (2n) – contains a
pair of each chromosome;
mitosis
 Haploid (n) – contains only
1 of each chromosome;
meiosis

Genes – sequence of DNA, that codes for a protein,
that determines a trait
 Genes are located on chromosomes (supercoiled
DNA)
 Humans have 46, or 23 “homologous” pairs
 Half from mom,
Half from Dad
Objective
 Illustrate the steps to meiosis
Warm-Up
1. Multiply (x + 5)(x – 5)
2. How many copies of a gene do body (autosomal)
cells have? How many do sex (gamete) cells
have?
EX. 2N = 4
MEIOSIS I




Prophase I
Tetrads form – homologous
chromosomes pair
Cross-Over occurs –
homologous chromosomes
exchange part of their
chromatin
 Produces new gene
combinations!
All other events same as
mitosis
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GENETIC VARIATION: CROSSING OVER

Homologous chromosomes group together
and exchange pieces.
Meiosis I
Crossing
over

MEIOSIS I




Metaphase I
Tetrads line up randomly
on the metaphase plate
 Increases variation!
Anaphase I
Homologous chromosomes
are pulled apart
http://www.youtube.com/watch?v=D1_mQS_FZ0&feature=related
MEIOSIS I



Telophase I
Same events as in mitosis
EXCEPT… now the
daughter cells are Haploid
Meiosis I
Interphase I
Prophase I
Metaphase I
Anaphase I
Telophase I
and
Cytokinesis
MEIOSIS II

Exactly like Mitosis; sister chromatids separate
Telophase I and
Cytokinesis I
Meiosis II
Prophase II
Metaphase II
Anaphase II Telophase II
and
Cytokinesis
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MEIOSIS

Four haploid cells (n) each have one chromosome.
Each cell has a different combination of
alleles.
GENETIC VARIATION: PRINCIPLE
OF
INDEPENDENT ASSORTMENT
GENETIC VARIATION: RANDOM
FERTILIZATION

HUMANS

There is a 50% chance that a particular gamete
will receive a maternal chromosome and a 50%
chance it will receive a paternal chromosome.
There are 23 pairs of chromosomes in human games
cells.
 Number of possible combinations of maternal
and paternal chromosomes= 223

Many possible combinations of male and female
gametes.
HUMANS

One human ovum (egg) represents approximately
8 million possible chromsome combinations.
Same is true for sperm. Thus, one sperm
fertilizing one egg results in 8 million x 8 million
recombination possibilities
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MEIOSIS SQUARE DANCE

MEIOSIS FOLDABLE
http://teachersites.schoolworld.com/webpages/DC
urry/life.cfm?subpage=1151190
MALES VS. FEMALES


3/22/13
Males produce 4 haploid gametes (sperm)
Females produce 1 haploid gamete (egg) + 3
“polar bodies”
3/25/13
Objective
 Illustrate meiosis
Warm-Up
 Subtract (5p2 – 3) – (2p3 – 3p2)
 What happens during prophase I that allows for
genetic variation?
AIMS is just
around the
corner!
Objectives
 Differentiate between mitosis and meiosis
Warm-Up
1. Simplify (2m2)(2m3)
2. What is the goal of meiosis I?
3. What is the goal of meiosis II?
MITOSIS VS. MEIOSIS
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EX. 2N = 4
MITOSIS VS. MEIOSIS
Mitosis
Meiosis
Type of cell
Body Cell
Sex cell
Beginning cell
Diploid (2n)
Diploid (2n)
Ending cell
Diploid (2n)
Haploid (n)
# of cells produced
2
4
# of chromosomes
Same as parent cell
Half as parent cell
Haploid
Diploid
Purpose
To make more body
cells
To make egg and
sperm
*Cross-Over
*Random
Orientation
Haploid
Identical
Different
MITOSIS VS. MEIOSIS

Meiosis:







MEIOSIS LAB
Random orientation of chromosomes
Crossing over
Random fertilization
Independent assortment
Occurs in 2 phases
Creates 4 different cells (haploid)
Mitosis:

Creates 2 genetically identical cells (diploid)
PRACTICE
A human has 23 pairs of chromosomes.
1. What is the diploid number?
2. What is the haploid number?
3. How many chromosomes are in an egg cell?
4. How many chromosomes are in a brain cell?
5. How many chromosomes are in a skin cell?
6. How many pairs of homologous chromosomes?
7. How many chromosomes in a cell produced by
mitosis?
8. How many chromosomes in a cell produced by
meiosis?
MEIOSIS
OREO COOKIE LAB PICTURES
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COOKIES
Blue: 1 Pair of Homologous Chromosomes
Pink: 1 Pair of Homologous Chromosomes
 Red: Nuclear Envelope
 Green: Meiotic Spindles
 Brown: Centrioles


PROPHASE I
METAPHASE I
COMPLETED
Blue: 1 Pair
of
Homologous
Chromosomes
 Pink: 1 Pair of
Homologous
Chromosomes
 Red: Nuclear
Envelope
 Green:
Meiotic
Spindles
 Brown:
Centrioles
OREO COOKIE LAB

ANAPHASE I
TELOPHASE I
ANAPHASE II
TELOPHASE II
Random orientation
Crossover
PROPHASE II
METAPHASE II
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PROBLEMS WITH
MEIOSIS
THIS IS WHAT YOUR CHROMOSOMES
LIKE DURING MITOSIS.
Scientists take a
picture of the
chromosomes, like
this one, and cut
then them out…
Nondisjunction
…AND THEN GROUP THEM TOGETHER BY
SIZE.
KARYOTYPES
Karyotype –
picture of
chromosomes
grouped as pairs
CALLED AN AMNIOCENTESIS.
Humans-46
chromosomes;
23 pairs
PROBLEMS SHOW UP WHEN THE BABY
HAS THE WRONG NUMBER OF
CHROMOSOMES.
LOOK
ARE MADE MOST OFTEN
DURING PREGNANCY IN A PROCEDURE
 Amniocentesis
–
The baby’s amniotic
fluid cells are taken
from the womb
through a needle,
and a karyotype is
made to look for
disorders.
THIS KARYOTYPE SHOWS THAT THE
21.
THIS CAUSES THE BIRTH DEFECT DOWN
SYNDROME.
PERSON HAS THREE OF CHROMOSOME
What
is
wrong with
this
karyotype?
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DOWN SYNDROME – “TRISOMY 21”

Children with Down
Syndrome have a variety of
problems, including mild
mental retardation, heart
problems, and many other
unusual physical
characteristics.
Nondisjunction – When chromosomes
fail to separate during meiosis.
Down Syndrome occurs when two sister
chromatids fail to separate during
anaphase of meiosis II. As a result,
some of the eggs or sperm produced
have too many chromosomes.
When a cell ends up with three copies of a
chromosome instead of two, this is called
trisomy. If a cell has only one copy, this is
called monosomy.
OTHER NONDISJUNCTION DISORDERS:
Triple
X Syndrome
Turner’s
Syndrome (XXX)
(X__)

Edward
Syndrome
(trisomy
 
Klinefelter’s
Syndrome
(XXY)

18)
 Males
w/an
X
 Girls
w/3
X extra
chromosomes







Girls
w/1 X
Only
5-10%
of live
births fertility
survive the
 Small
testicles,
reduced
Tall,
but
normal
physical
and
st year
stature,
swelling,
sterility
1Short
of life
sexual
characteristics
Many abnormalities in internal
organs
and external
Increased
risk of structures
learning
disabilities
Slow speech and motor
development
NONDISJUNCTION IS MOST LIKELY TO HAPPEN
IN OLDER MOTHERS, BECAUSE THEIR EGGS
HAVE BEEN IN THEIR BODIES SINCE BEFORE
BIRTH, AND ARE MORE LIKELY TO HAVE
PROBLEMS DIVIDING.
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KARYOTYPING ACTIVITY
Map each karyotype and
determine if it is male or
female?
 What is its genetic disorder?

Options:
Klinfelter’s syndrome (XXY)
 Edward’s syndrome (trisomy 18)
 Down syndrome (trisomy 21)
 Trisomy 13


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