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Chapter 11
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.
bud
Hydra
Yeast
Fragmentation is the splitting of the parent into pieces that each grow into a new organism.
• Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.
Sea Stars
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.
Sexual
Reproduction
Asexual
Reproduction
Benefits
Costs
Let’s Compare Sexual and 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?
46 92
sperm(father)
egg(mother)
zygote(cell)
Human - 23 pair (23 from each parent)Fruit fly - 8 pairGarden pea - 14 pair
Recall that each chromosome contains thousands of genesthat 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!
23egg
(mother) 46
zygote(cell)
sperm(father)
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
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)
KEY CONCEPT Gametes have half the number of chromosomes that body cells have.
• 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.
Meiosis reduces chromosome number and creates genetic diversity.
KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells.
Meiosis I and meiosis II each have four phases, similar to those in mitosis.
homologous chromosomes
sisterchromatids
sisterchromatids
– Pairs of homologous chromosomes separate inmeiosis I.
– Homologous chromosomes are similar but not identical.
– Sister chromatids divide in meiosis II.
– Sister chromatids are copies of the same chromosome.
• 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 andmeiosis 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!
223 X 223 or 70 trillion different combinations!!!
That’s a lot of variety!
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 Gametes
(sex cells)
Somatic cells
(all other cells)
# of chromosomes (n)
Come from
# of cells from one parent cell
Process
Purpose
# of divisions
Genetic info
Type of cell Gametes
(Sex Cells)
Somatic cells
(all other cells)
# of chromosomes n
haploid
2n
diploid
Come from Germ cells Somatic cells
# of cells from parent cell
4 sperm or
1 egg
2
Process meiosis mitosis
Purpose Reproduction All other
# of divisions 2 1
Genetic info Shuffled around identical
MeiosisOccurs in two phases:
Meiosis I
Meiosis II
Genetic information is shuffled around.
Results in four different haploiddaughter cells
Occurs in sex cells
MitosisOccurs in one phase.
Genetic information remains the same.
Results in two identical diploid daughter cells.
Occurs in somatic cells
Meiosis vs. Mitosis
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
