Transcript 5.4 Asexual Reproduction

5.4 Asexual Reproduction
5.1 Cell Cycle
KEY CONCEPT
Cells have distinct phases of growth, reproduction,
and normal functions.
5.4 Asexual Reproduction
5.1 Cell Cycle
Cells divide at different rates.
• The rate of cell division varies with the types of cells.
5.3
Regulation
of the Cell Cycle
5.4 Asexual
Reproduction
KEY CONCEPT
Cell cycle regulation is necessary for healthy
growth.
5.3
Regulation
of the Cell Cycle
5.4 Asexual
Reproduction
• External factors include physical and chemical signals.
• Growth factors are proteins that stimulate cell division.
5.4 Asexual Reproduction
5.1 Cell Cycle
Cell size is limited.
• If volume increases faster than surface area then cell
divides
5.3
Regulation
of the Cell Cycle
5.4 Asexual
Reproduction
• Apoptosis is programmed cell death.
– a normal feature of healthy organisms
– occurs in development of infants
webbed fingers
5.4 Asexual Reproduction
KEY CONCEPT
Many organisms reproduce by cell division.
5.4 Asexual Reproduction
Asexual reproduction is the creation of offspring from a
single parent.
– Binary fission produces two daughter cells genetically
identical to the parent cell.
– occurs in prokaryotes (bacteria)
parent cell
DNA
duplicates
cell begins
to divide
daughter
cells
5.4 Asexual Reproduction
• Budding forms a new organism from a small projection
growing on the surface of the parent.
Hydra
bud
Yeast
5.4 Asexual Reproduction
• Vegetative reproduction
forms a new plant from the
modification of a stem or
underground structure on
the parent plant.
5.4 Asexual Reproduction
5.1 Cell Cycle
The cell cycle has four main stages.
5.4 Asexual Reproduction
5.1 Cell Cycle
Interphase
– Gap 1 (G1): cell growth and
normal functions
– Synthesis (S): copies DNA
– Gap 2 (G2): additional
growth
– Mitosis (M): includes
division of the cell nucleus
– cytokinesis - division of the
cell cytoplasm
• Some cells (G0) – exit the cell cycle
•
- fully developed cells in the CNS
5.2
Mitosis Reproduction
and Cytokinesis
5.4 Asexual
Mitosis produces two genetically identical daughter cells.
Parent cell
centrioles
spindle fibers
centrosome
nucleus with
DNA
5.2
Mitosis Reproduction
and Cytokinesis
5.4 Asexual
• Mitosis divides the cell’s nucleus in four phases.
• First phase
– During prophase, chromosomes condense and
spindle fibers form.
• Nucleolus and the nuclear membrane break down &
disappear
• Centrioles (centrosomes) appear
• Centrioles move toward opposite poles of the cell
5.4 Asexual Reproduction
5.2
Mitosis Reproduction
and Cytokinesis
5.4 Asexual
• Second phase
– During metaphase, chromosomes line up in the
middle of the cell.
– Chromosomes are easier to identify
5.4 Asexual Reproduction
5.2
Mitosis Reproduction
and Cytokinesis
5.4 Asexual
• Third phase
– During anaphase, sister chromatids separate to
opposite sides of the cell.
5.4 Asexual Reproduction
5.2
Mitosis Reproduction
and Cytokinesis
5.4 Asexual
• Fourth phase
During telophase, the new nuclei form and chromosomes
begin to uncoil.
Spindle fibers disassemble
5.4 Asexual Reproduction
5.2
Mitosis Reproduction
and Cytokinesis
5.4 Asexual
• Cytokinesis differs in animal and plant cells.
In animal cells, the
membrane pinches
closed
– cleavage furrow
In plant cells, a cell
wall forms
– cell plate
5.2
Mitosis Reproduction
and Cytokinesis
5.4 Asexual
Results of Mitosis
•
•
•
•
2 new cells genetically identical to the parent cell
2 identical diploid cells.
Single celled eukaryote – asexual reproduction
Multi-celled eukaryote – growth
5.4 Asexual
Reproduction
6.1
Chromosomes
and Meiosis
• Meiosis makes haploid cells from diploid cells.
– Meiosis occurs in sex cells - gametes
– Meiosis produces genetically different gametes.
5.4
Reproduction
6.2Asexual
Process
of Meiosis
KEY CONCEPT
During meiosis, diploid cells undergo two cell
divisions that result in 4 different haploid cells.
5.4
Reproduction
6.2Asexual
Process
of Meiosis
Stages of Meiosis
Interphase – G1, S, G2
Meiosis I
1.
Prophase I
•
DNA coils tightly into chromosomes
•
Spindle fibers appear
•
Nucleus & nucleolus disappear
•
Every chromosome lines up next to its homologue – synapsis
- each pair of homologous chromosome is called a tetrad –
4 chromatids
XX
- during synapsis the chromatids within a homolgous pair twist around
each other – portions of chromatids may break off & attach to adjacent
chromatids – crossing over
* permits the exchange of genetic material between maternal &
paternal chromosomes = genetic recombination
6.6
Meiosis and
Genetic Variation
5.4 Asexual
Reproduction
6.6
Meiosis and
Genetic Variation
5.4 Asexual
Reproduction
Metaphase I
• Tetrads line up randomly along the middle of the cell
6.6
Meiosis and
Genetic Variation
5.4 Asexual
Reproduction
Anaphase I
• Tetrads separate
• Each homologous chromosome moves to an opposite
pole
• Independent Assortment – random separation of the
homologous = genetic recombination
6.6
Meiosis and
Genetic Variation
5.4 Asexual
Reproduction
Telophase I
• Chromosome reach the opposite pole
• Cytokinesis begins
• Each new cells contain a haploid # of chromosomes (half
the original #)
5.4
Reproduction
6.2Asexual
Process
of Meiosis
• DNA is not replicated between meiosis I and
meiosis II (No Interphase)
5.4
Reproduction
6.2Asexual
Process
of Meiosis
Meiosis II
1.
Prophase II
•
Spindle fibers and centrioles form
2.
Metaphase II
•
Chromosomes move to the middle of the cells
3.
Anaphase II
•
Chromatids separate & move toward opposite poles
4.
Telophase II
•
Nuclear membrane forms around the chromosomes
Cytokinesis II – results in 4 new cells each with half the # of chromosomes
5.4
Reproduction
6.2Asexual
Process
of Meiosis
– Meiosis has two cell divisions while mitosis has one.
– Meiosis results in haploid cells; mitosis results in diploid
cells.
5.4
Reproduction
6.2Asexual
Process
of Meiosis
Haploid cells develop into mature gametes.
• Gametogenesis is the production
of gametes.
• Gametogenesis differs between
females and males.
5.4
Reproduction
6.2Asexual
Process
of Meiosis
Spermatogenesis – production of sperm cells
• Diploid reproductive cell divides to form four haploid cells
– spermatids
• Each spermatid then develops into a mature sperm cell
• sperm cells – spermatozoa
5.4
Reproduction
6.2Asexual
Process
of Meiosis
Oogenesis – production of mature egg cells - ova
• Diploid reproductive cell divides to produce one mature
egg cell (ovum)
• During cytokinesis I & II the cytoplasm of the cell is
divided unequally
• One cell receives most of the cytoplasm and develops
into a mature egg cell
• Other 3 products = polar bodies = degenerate (break
down)