Download Meiosis - Juanita Biology

Meiosis
How sex cells are made!
Asexual vs. Sexual Reproduction
A.
Asexual reproduction - quick and efficient.
1. Don’t need a partner.
2. But your offspring are all
clones— no variation!
Sex is not for everyone:
• Because the environment is always changing, some offspring
may not be as well adapted as the parents.
• Sex can be dangerous - spreading disease, risk of predation
• Sex requires energy to find a mate
Why sex?
B. Sexual reproduction- takes more energy!
1.You and your mate must find each other
2. Must exchange genetic material.
3. It is energetically expensive to construct and use mateattracting body parts.
Bottom Line: Why is sexual reproduction so AWESOME
for you?
Because you and your mate BOTH pass characteristics to all
your offspring, there will be natural VARIATION
(differences) introduced by sex. These variations give your
offspring selective advantages for survival in changing
environments.
This will be
important when
we study
EVOLUTION!
Hint hint!
Variation thanks to sexual reproductionall these puppies are slightly different
genetically even though they had the
same parents
Intro to Genetics
What will we study in the next few days?
1. Meiosis- the process that makes sex cells which
carry YOUR genetic info into your offspring
2. Karyotypes- what your chromosomes look like
3. Understanding how your genes get passed on
4. Linking genetics to evolution (next chapter)
Genetics- “to generate”
• Genetics is the branch of biology that deals
with the study that explains how organisms
inherit characteristics- inheritance may
come from sexual or asexual reproduction.
• Asexual reproduction- mitotic division
• Sexual reproduction- meiotic divisions
Two things are required in order for
genetics to work:
1. You must inherit a single
copy of every gene from both
your parents. Since you have
two biological parents, you
will have TWO complete sets
of genes.
2. When YOU make your own
gametes (sex cells), your two
sets of genes must be
separated from each other.
Each of your gametes will
have only one set of genes.
http://www.web-books.com/eLibrary/Medicine/Neonatal/Images/CF_Inheritance.gif
Chromosome Number
• Diploid (2N) – 2
copies of each
chromosome
• Haploid (1N) – 1
copy of each
chromosome
• Homologous
chromosomes –
chromosomes that
have same size, shape
& gene sequence
Chromosome NumberSomatic cell (human)
• Diploid (2N) – 46
• Haploid (1N) – 23
• Homologous
chromosomes – 23
pairs of
homologues
• Is this a karyotype
of a somatic cell or
gamete?
Diploid vs. Haploid
1. Diploid- 2 sets of
info; 1 set of
chromosomes from
mom, other set from
dad; ONLY
SOMATIC CELLS
2. Haploid- 1 set of
genetic info; 1 set of
chromosomes; ONLY
GAMETES!
http://www.web-books.com/eLibrary/Medicine/Neonatal/Images/CF_Inheritance.gif
How do organisms make gametes (1N) from
germ cells (2N)?
Meiosis- a process that:
• produces gametes
• is a “reduction division”- reduces the chromosome
number in half (2N  1N)
• A diploid cell results in 4 UNIQUE and VARIED
haploid cell
• 2 divisions
Overview of
Meiosis
You and your siblings all have:
50% genetic info from mom
50% genetic info from dad
Why don’t all of you look the
same?
•
http://www.diffen.com/difference/
Meiosis_vs_Mitosis
CROSSING OVER*genetic “shuffling” of info
*nonsister chromatids cross parts
of themselves during Prophase I
of the first meiotic division
(Meiosis I)
*genetic recombination occursyou end up with gametes that are
all a little different but still 50%
mom and 50% dad info
Lab- “Meiosis Phases Activity”
•
•
•
Grab your lab books. Title activity as above.
Name, date, period.
You will work individually.
A.
B.
C.
D.
E.
F.
Cut out each phase of meiosis.
Paste/tape the phases in order (book pg. 276-7)
Name each phase
Describe what is occurring at each phase.
Label “Meiosis I” and “Meiosis II”
Answer the following questions:
1. What is the importance of meiosis.
2. List 3 ways meiosis is DIFFERENT from mitosis.
3. List 2 ways meiosis is SIMILAR to mitosis.
Links to check out – useful info
and animations
• http://www-bcf.usc.edu/~forsburg/meiosis.html
• http://www.youtube.com/watch?v=Z0ujlwWQXzM
• http://meiosistheprocess.wikispaces.com/Meiosis+Video
(this site has lots of great options for learning meiosis!)
• http://www.hhmi.org/bulletin/nov2008/features/ (a very
good reading that gets into the details)
• http://mercury.bio.uaf.edu/~kevin_mccracken/genetics/labs
/lab1/lab-1b.pdf (helpful notes on all the phases)
Interphase I
• DNA Replication
occurs (exact copy of
DNA made)
Prophase I
• Chromosomes pair
with their homologous
chromosomes
• Crossing-over:
exchange of alleles
between homologous
chromosomes
Metaphase I
• Homologous
chromosomes line up
on equator
• Spindle fibers attach
to centromeres
Anaphase I
• Homologous
chromosomes separate
Telophase I & Cytokinesis
• Nuclear membrane
reforms
• Cell separates into 2
cells
• Daughter cells are
haploid
• Chromosome sets and
alleles unique in each
cell
Prophase II
• 2 haploid cells
• No chromosome
replication
• Each chromosome has
2 chromatids
Metaphase II
• Chromosomes line up
on equator
• Spindle fibers attach at
the centromere
Anaphase II
• Sister chromatids
separate
• Chromatids pulled to
opposite poles
Telophase II & Cytokinesis
• New nuclear
envelopes reform
• 4 daughter cells
• All are haploid, 1N
(one set of
chromosomes)
• Non-identical
(different alleles)
Gamete formation
In males, meiosis
produces 4 sperm
In females, meiosis
produces 1 egg and 3
polar bodies
Comparing Mitosis & Meiosis
Mitosis
Meiosis
Creates 2 diploid cells
Creates 4 haploid cells
2 daughter cells with identical sets
of chromosomes and alleles
4 daughter cells with different
alleles on each chromosome
Allows organism to grow and
replace cells
Allows organisms to produce
How organisms reproduce asexually gametes for sexual reproduction
Animation
http://kvhs.nbed.nb.ca/gallant/biology/mitosis_meiosis.html