Regents Biology 2006-2007 Unit 6 : Meiosis & Sexual Reproduction
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Regents Biology 2006-2007
Unit 6 : Meiosis &
Sexual Reproduction
Regents Biology
Cell division / Asexual reproduction
Mitosis
produce cells with same information
identical daughter cells
exact copies
clones
same number of chromosomes
same genetic information
Aaaargh! I’m seeing double!
Regents Biology
Asexual reproduction
Single-celled eukaryotes
yeast
Paramecium
Amoeba
Simple multicellular eukaryotes
Hydra budding
What are the disadvantages of
asexual reproduction?
What are the advantages?
Regents Biology
Review : Mitosis aka identical
cells!
Regents Biology
How about the rest of us?
What if a complex multicellular organism
(like us) wants to reproduce?
joining of egg + sperm
Do we make egg & sperm by mitosis?
46 46 + 92
egg sperm zygote
What if we did, then….
Doesn’t work!
No!
Regents Biology
Human female karyotype
46 chromosomes
23 pairs
XX
diploid = 2 copies 2n
Regents Biology
46 chromosomes
23 pairs
XY
Human male karyotype diploid = 2 copies 2n
Regents Biology gametes
How do we make sperm & eggs?
Must reduce 46 chromosomes 23
must half the number of chromosomes
haploid
23
23 46
egg
sperm
46
meiosis 46
fertilization
23
23
zygote
Regents Biology
Meiosis makes sperm & eggs
46 chromosomes to 23 chromosomes
half the number of chromosomes
23
23 46
egg
sperm
46
meiosis
haploid diploid
Regents Biology
Practice:
Compared to human cells resulting from
mitotic cell division, human cells resulting
from meiotic cell division would have
•twice as many chromosomes
•the same number of chromosomes
•one-half the number of chromosomes
•one-quarter as many chromosomes
Regents Biology
Regents Biology
Paired chromosomes Homologous chromosomes
both chromosomes of a pair carry “matching” genes control same inherited characters
homologous = same information
diploid
2n
2n = 4
homologous
chromosomes
double stranded
homologous chromosomes
eye color
(brown?)
eye color
(blue?)
Regents Biology
Meiosis 1 overview
1st division of meiosis
4 chromosomes
diploid
2n 2 chromosomes
haploid
1n
double stranded
Copy DNA Line Up 1
Divide 1
gamete
prophase 1 metaphase 1
telophase 1
Regents Biology
2nd division of meiosis
looks like mitosis
Meiosis 2 overview
2 chromosomes haploid 1n
4
gametes
Line Up 2
Bye Bye 2
telophase 1
metaphase 2
telophase 2
Regents Biology
Meiosis = reduction division
Meiosis
special cell division in sexually
reproducing organisms
reduce number of chromosomes
2n 1n
diploid haploid
half
makes gametes
sperm, eggs
Regents Biology
Meiosis & mitosis
Meiosis to
make gametes
sperm & egg
Mitosis to make
copies of cells
growth
repair
development
Regents Biology
Sexual reproduction lifecycle
1 copy
haploid
1n
2 copies
diploid
2n
1 copy
haploid
1n
meiosis fertilization
We’re mixing things up here! A good thing?
Regents Biology
mitosis
zygote
Putting it all together…
23
23 46
egg
sperm
46
meiosis 46 23
23
fertilization mitosis & development
meiosis fertilization mitosis + development
46
46
46
46
46
46
46 46
gametes
Regents Biology
The value of meiosis 1
Consistency over time
meiosis keeps chromosome number same
from generation to generation
from Mom
from Dad
offspring Dad
Mom
Regents Biology
The value of meiosis 2
Change over time
meiosis introduces genetic variation
gametes of offspring do not have
same genes as gametes from parents
new combinations of traits
from Mom
from Dad
new gametes made by offspring
offspring
We’re mixing things
up here!
variation
Regents Biology
Practice:
The great variety of possible gene
combinations in a sexually reproducing
species is due in part to the
1. sorting of genes as a result of gene
replication
2. pairing of genes as a result of mitosis
3. pairing of genes as a result of
differentiation
4. sorting of genes as a result of meiosis
Regents Biology
Regents Biology
How does this explain:
family resemblance & differences! Why are the kids so similar to the parents but not exact?
Regents Biology 2006-2007
Any Questions??
What are the DISadvantages of
asexual reproduction?
What are the DISadvantages of
sexual reproduction?
What are the advantages of
sexual reproduction?
What are the advantages of
asexual reproduction?
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