Warm-Up Questions
1. What are the stages of mitosis in order?
2. The diagram represents a cell process.
Which statement regarding this process is true?
A. Cell B contains the same genetic information that cells A and C
contain
B. Cell C has DNA that is only 50% identical to cell B
C. Cell A has DNA that is only 75% identical to cell C
D. Cells A, B, and C contain completely different genetic information
3. How many chromosomes do most human cells have?
Warm-Up Questions: Check your answers
1.
What are the stages of mitosis in order?
Prophase, Metaphase, Anaphase, and Telophase
2. The diagram represents a cell process.
Which statement regarding this process is true?
A. Cell B contains the same genetic information that cells A and C contain
B. Cell C has DNA that is only 50% identical to cell B
C. Cell A has DNA that is only 75% identical to cell C
D. Cells A, B, and C contain completely different genetic information
A
3. How many chromosomes do most human cells have?
46 total chromosomes
FYI:
1. The Cell Division test is on
Monday!
2. We’ll have an open note quiz
tomorrow, but you only get one try!
3.The midterm is next Wednesday!
What to do:
1. Complete the guided notes using the PDF
at
http://shimkoscience.weebly.com/biology.
html
2. Fill out the review questions using the
information you learned
3. Go to the online textbook (through
Canvas) and complete the “Cellular
Reproduction” Chapter in LearnSmart
Meiosis &
Sexual Reproduction
2006-2007
Cell division / Asexual reproduction
• Mitosis (asexual reproduction)
– produces cells with same information
• identical daughter cells
– exact copies
• clones
– same number of chromosomes
• same genetic information
-used by single cell organisms and somatic
(body) cells
• like bacteria or skin cells
Aaaargh!
I’m seeing
double!
How about more complex organisms?
1. Mitosis is good for simple organisms, but what if
a complex multicellular organism (like us) wants to
reproduce?
– joining of egg + sperm (fertilization)
2. Do we make egg & sperm by mitosis?
No!
What if we did, then….
46
egg
+
46
92
sperm
zygote
Doesn’t work!
3. Meiosis makes sperm & eggs
4. In humans: 46 homologous chromosomes to 23 single
chromosomes (half the number of chromosomes)
23
46
meiosis
46
diploid
egg
23
sperm
haploid
5. What are Paired/ Homologous chromosomes?
• Homologous chromosomes
– both chromosomes of a pair carry “matching” genes
• control same inherited characters
• 6. homologous = same information
diploid
2n
2n = 4
eye color
(brown?)
eye color
(blue?)
homologous
chromosomes
double stranded
homologous chromosomes
7. Egg cells and sperm cells are
called “haploid” because they
only have a single set of
chromosomes.
8. Diploid vs. Haploid Cell
Diploid
• full set of chromosomes (2n)
• mitosis
• all cells but gametes (sex cells)
Haploid
• half set of chromosomes (n)
• meiosis
• gametes only
9. How do we create haploid cells?
Meiosis = reduction division
10. Meiosis
A. special cell division in sexually
reproducing organisms
B. reduce number of chromosomes
• 2n  1n
• diploid  haploid
– half
C. makes gametes
• sperm, eggs
What actually happens during
meiosis?
11. How do we make sperm & eggs?
• Must reduce 46 chromosomes  23
– must half the number of chromosomes
– haploid
23
46
meiosis
zygote
23
46
egg
23
46
23
sperm
gametes
fertilization
12. Meiosis I (very similar to mitosis)
Copy DNA
and
crossing
over
occurs
Chromosomes
Line Up
Cell Divides
12. Meiosis II (2): Kind of like meiosis I,
except the DNA doesn’t replicate before
Chromosomes
Line Up
Cell Divides
12. It looks like this when it’s
combined
13. Meiosis Summary:
Interphase: Before meiosis begins, genetic
material is duplicated.
First division of meiosis (Meiosis I)
– Prophase 1: DNA condenses into
chromosomes. Crossing-over can occur
during the latter part of this stage.
– Metaphase 1: Homologous
chromosomes align in the middle
(Meta=middle)
– Anaphase 1: Homologous pairs separate
and move towards the poles.
– Telophase 1: Two daughter cells are
formed with each daughter containing
only one chromosome of the
homologous pair.
Second division of meiosis: Gamete formation
(Meiosis II)
– Prophase 2: DNA does not replicate.
– Metaphase 2: Chromosomes align at
the equatorial plate (in the middle).
– Anaphase 2: Sister chromatids migrate
separately to each pole.
– Telophase 2: Cell division is complete.
Four haploid daughter cells are
obtained.
How does meiosis lead to a new
organism?
14. How does meiosis lead to a new organism?
meiosis  fertilization  mitosis + development
gametes
46
meiosis
23
23
egg
23
46
23
zygote
fertilization
sperm
46
46 46
46 46 46
46
46
46
mitosis
&
mitosis
development
15. Cycle of Life: (when do the different
types of cell division happen during our lives?)
Fertilization
What do these 46 human chromosomes
look like in real life?
16. “Karyotypes” are used to see the number and
appearance of the chromosomes an organism has
Random Fact:
• The sperm cell (male sex cell) determines the sex of
the offspring. The 23rd chromosomes (X or Y) is the
genetic difference between men and women.
Karyotype: Human Female (Female because it
has two X chromosomes, no Y)
Notice:
There are
23 pairs of
chromosomes
23x2=46
total
Karyotype: Human Male (Male because it
has X and Y chromosomes)
Notice:
There are
23 pairs of
chromosomes
23x2=46
total
17. How
does
meiosis
increase
genetic
variation?
1.
2.
3.
How does meiosis create genetic variation?
18. Advantages of Meiosis- it
increases genetic variation
No two offspring (except identical
twins) are the same, giving the
species a better chance of
surviving.
19. Disadvantage of Meiosisorganisms cannot reproduce by
themselves, and it takes more time
and energy to reproduce/ find a
partner to reproduce with.
Congrats! You finished with the notes!
Now, please flip your note paper to the
back:
1) get a textbook and answer the guided
reading questions.
2) Use these last two slides to help you
answer the other review questions on
the paper.
Meiosis & mitosis
• Meiosis to make
gametes
– sperm & egg
• Mitosis to make
copies of cells
– growth
– repair
– development
Reproduction Review:
Sexual Reproduction
· 2 parents - male and
female
· involves gametes - sperm
and egg
· offspring genetically
different
· can be internal or
external fertilization
· MEIOSIS
Asexual Reproduction
· 1 parent
· offspring produced by a
“part” or “division” of the
parent
· CLONES - offspring
genetically identical
· MITOSIS
What to do next:
1. Go to the online textbook (through
Canvas) and complete the “Cellular
Reproduction” Chapter in LearnSmart