Transcript meiosis notes

Chapter 11
Chapter 11
 Some eukaryotes reproduce through mitosis.
 Binary fission is similar in function to mitosis.
 Asexual reproduction is the creation of offspring from a single
parent.
 Binary fission produces two daughter cells genetically identical to the
parent cell.
 Binary fission occurs in
prokaryotes.
parent cell
DNA
duplicates
cell begins
to divide
daughter
cells
 Budding forms a new organism from a small projection
growing on the surface of the parent.
Hydra
bud
Yeast
 Fragmentation is the
splitting of the parent into
pieces that each grow into a
new organism.
Sea Stars
• Vegetative reproduction forms a new
plant from the modification of a stem
or underground structure on the
parent plant.
 Parthenogenesis - female makes fertile egg (lizard,
snake, cricket)
(Biology Letters, DOI: 10.1098/rsbl.2010.0793).
Benefits of Asexual Reproduction
• No energy wasted on
making gametes.
• No energy wasted on
finding a mate.
• Faster, more efficient.
 All offspring are identical and have identical
weaknesses. If environment changes, all may die.
http://www.diveasia.com/images/097ss.jpg
 Two parents give DNA to
offspring
 Zygote = union of 2 gametes
(sex cells) by fertilization
 Most eukaryotes reproduce
sexually
http://zakstar.files.wordpress.com/2008/05/zygote.jpg
 Increases variation through:
 Crossing over: exchange of genetic
material between homologous
chromosomes
 Independent assortment: random
distribution of homologous
chromosomes during meiosis.
 Random fertilization: egg and
sperm meet randomly
http://www.virtuallaboratory.net/Biofundamentals/lectureNotes/AllGraphics/Snail%20Shell%20Variation.gif
Why is variety good?
If the environment
changes, some of the
offspring might survive if
they have different traits
that are useful.
http://www.physorg.com/newman/gfx/news/extentofinbr.jpg
 Spend energy
making gametes
 Spend energy
finding a mate
 Takes more time to
do these things
http://image09.webshots.com/9/1/46/73/117414673tdPQED_fs.jpg
 Environment determines what form of reproduction is
most advantageous.
– Asexual reproduction is
an advantage in
consistently favorable
conditions.
– Sexual reproduction is an
advantage in changing
conditions.
Let’s Compare Sexual and Asexual Reproduction:
Sexual
Reproduction
Benefits
Costs
Asexual
Reproduction
If a new human is created from the union of two cells (one
from the father and mother)…
How do you avoid doubling the chromosome number each
time?
egg
sperm
(father)
(mother)
46
92
zygote
(cell)
 Human - 23 pair (23 from each parent)
 Fruit fly - 8 pair
 Garden pea - 14 pair
Recall that each chromosome contains thousands of genes
that determine different traits.
http://www.ncbi.nlm.nih.gov/mapview/map_search.cgi?taxid=
9606
•The Genetic material (chromosomes) come in pairs.
HOMOLOGOUS
•
chromosomes are
chromosomes that carry the same information on them
•Example: hair color
•One of the homologous chromosomes may carry
the information for blonde hair and another for
brown hair.
• Your cells have autosomes and sex
chromosomes.
• Your body cells have 23 pairs of
chromosomes.
– Homologous pairs of chromosomes
have the same structure.
– For each homologous pair, one
chromosome comes from each parent.
• Chromosome pairs 1-22 are autosomes.
• Sex chromosomes, X and Y, determine
gender in mammals.
An arrangement of
photographs of
chromosomes in order
from largest to smallest
using a stained
chromosome spread.
 Body cells are diploid; gametes are haploid.
 Fertilization between egg and sperm occurs in sexual
reproduction.
 Diploid (2n) cells have two copies of every chromosome.
 Body cells are diploid.
 Half the chromosomes come from each parent.
How can you avoid doubling your chromosome
number each time?
Each sperm & egg contain half (n) the number of
chromosomes of all other cells!
sperm
(father)
23
egg
(mother)
46
zygote
(cell)
So, when 2 gametes join, the zygote has the correct number
(2n) of chromosomes.
• Haploid (n) cells have one copy of every chromosome.
– Gametes are haploid.
– Gametes have 22 autosomes and 1 sex chromosome.
Diploid cells are cells that have two of each
chromosome. Most of the cells that make
up your body are diploid.
Haploid cells are cells
that have only one of
each chromosome .
Female egg cells and
male sperm cells are
haploid cells
– When one haploid gamete combines with another haploid
gamete its called fertilization.
Chapter 11
KEY CONCEPT
Gametes have half the number of chromosomes that body cells have.
 You have body cells and gametes.
 Body cells are also called somatic cells.
 Germ cells develop into gametes.
 Germ cells are located in the ovaries and testes.
 Gametes are sex cells: egg and sperm.
 Gametes have DNA that can be passed to offspring.
body cells
sex cells (sperm)
sex cells (egg)
• Chromosome number must be maintained in animals.
• Many plants have more than two copies of each
chromosome.
• Mitosis and meiosis are types of nuclear division that
make different types of cells.
• Mitosis makes more diploid cells.
• Meiosis makes haploid cells from diploid cells.
– Meiosis occurs in sex cells.
– Meiosis produces gametes.
KEY CONCEPT
During meiosis, diploid cells undergo two cell divisions that result in haploid cells.
 Meiosis reduces chromosome number and creates
genetic diversity.
 Meiosis I and meiosis II each have four phases, similar
to those in mitosis.
– Pairs of homologous chromosomes separate in
meiosis I.
– Homologous chromosomes are similar but not identical.
– Sister chromatids divide in meiosis II.
– Sister chromatids are copies of the same chromosome.
homologous chromosomes
sister
chromatids
sister
chromatids
• Meiosis I occurs after DNA has been replicated.
• Meiosis I divides homologous chromosomes in four phases.
 Homologous chromosomes
exchange sections of DNA
in a process is called
crossing over during
Prophase I
• Meiosis II divides sister chromatids in four phases.
• DNA is not replicated between meiosis I and
meiosis II.
• Meiosis differs from mitosis in significant ways.
– Meiosis has two cell divisions while mitosis has one.
– In mitosis, homologous chromosomes never pair up.
– Meiosis results in haploid cells; mitosis results in diploid
cells.
Why don’t you and your siblings look exactly the
same?
Because not all of the gametes that a person
makes are identical.
1. Random Fertilization
Egg and sperm meet randomly!
 Chromosomes from mom and dad don’t always end up
on the same side during metaphase II, they have
independent assortment
 homologous
chromosomes exchange
sections of DNA in a
process is called crossing
over during Prophase I
Type of cell
# of chromosomes
(n)
Come from
# of cells from one
parent cell
Process
Purpose
# of divisions
Genetic info
Gametes
(sex cells)
Somatic cells
(all other cells)
Type of cell
Gametes
(Sex Cells)
Somatic cells
(all other cells)
# of chromosomes
n
haploid
Germ cells
2n
diploid
Somatic cells
2
Process
4 sperm or
1 egg
meiosis
mitosis
Purpose
Reproduction
All other
# of divisions
2
1
Genetic info
Shuffled around
identical
Come from
# of cells from
parent cell
Meiosis vs. Mitosis
Meiosis
Occurs in two phases:
 Meiosis I
 Meiosis II
Genetic information
is shuffled around.
Results in four
different haploid
daughter cells
Occurs in sex cells
Mitosis
Occurs in one phase.
Genetic information
remains the same.
Results in two
identical diploid
daughter cells.
Occurs in somatic
cells
Chapter 11
 All the events in the growth and development to
maturity of an organism
 Diploid Life cycle: multicellular organism is diploid,
haploid stage is single cell gamete. (animals)
 Haploid Life cycle: multicellular organism is haploid,
diploid stage is single cell. (fungi, some protists)
http://faculty.irsc.edu/FACULTY/TFischer/bio%201%20files/human%20life%20cycle.jpg
http://www.baileybio.com/plogger/images/ap_biology/powerpoint_-_introduction_to_plants/fern_-_life_cycle.jpg
http://microbewiki.kenyon.edu/images/3/3f/31-07-ZygomyceteLifeCyc-L.jpg