Regents Biology - Valhalla High School
Download
Report
Transcript Regents Biology - Valhalla High School
Meiosis &
Sexual Reproduction
Regents Biology
2006-2007
Cell division / Asexual reproduction
Mitosis
produce cells with same information
identical daughter cells
exact copies
clones
same number of chromosomes
same genetic information
Regents Biology
Asexual reproduction
Single-celled eukaryotes
yeast
Paramecium
Amoeba
Simple multicellular
eukaryotes
Hydra
budding
What are the
disadvantages of
asexual reproduction?
Regents Biology
What are the
advantages?
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? No!
What if we did, then….
46
egg
Regents Biology
+
46
92
sperm
zygote
Doesn’t work!
diploid = 2 copies 2n
Human female karyotype
46 chromosomes
23 pairs
XX
Regents Biology
diploid = 2 copies 2n
Human male karyotype
46 chromosomes
23 pairs
XY
Regents Biology
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
Regents Biology
23
sperm
gametes
fertilization
Meiosis makes sperm & eggs
46 chromosomes to 23 chromosomes
half the number of chromosomes
23
46
meiosis
46
diploid
Regents Biology
egg
23
sperm
haploid
Paired chromosomes
Homologous chromosomes
both chromosomes of a pair carry “matching” genes
control same inherited characters
homologous = same information
diploid
2n
2n = 4
Regents Biology
eye color
(brown?)
eye color
(blue?)
homologous
chromosomes
double stranded
homologous chromosomes
double
stranded
Meiosis 1 overview
1st division of meiosis
Copy DNA
Line Up 1
prophase 1
metaphase 1
4 chromosomes
diploid
2n
Regents Biology
Divide 1
gamete
telophase 1
2 chromosomes
haploid
1n
Meiosis 2 overview
telophase 2
telophase 1
2nd division of meiosis
looks like mitosis
2 chromosomes
haploid
Regents Biology
1n
metaphase 2
gametes
4
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
2 copies
diploid
2n
1 copy
haploid
1n
fertilization
meiosis
We’re mixing
things up here!
A good thing?
Regents Biology
1 copy
haploid
1n
Putting it all together…
meiosis fertilization mitosis + development
gametes
46
meiosis
23
23
egg
23
46
23
zygote
fertilization
sperm
Regents Biology
46
46 46
46 46 46
46
46
46
mitosis
&
mitosis
development
The value of meiosis 1
Consistency over time
meiosis keeps chromosome number same
from generation to generation
from Mom
Mom
Dad
offspring
from Dad
Regents Biology
The value of meiosis 2
Change over time
We’re
mixing things
up here!
meiosis introduces genetic variation
gametes of offspring do not have
same genes as gametes from parents
new combinations of traits
from Dad
variation
from Mom
offspring
Regents Biology
new gametes made by offspring
What are the
advantages of
asexual reproduction?
What are the
DISadvantages of
asexual reproduction?
Any Questions??
What are the
advantages of
sexual reproduction?
Regents Biology
What are the
DISadvantages of
sexual reproduction?
2006-2007