mitosis
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Mitosis. How Cells Reproduce. Types of Cells. The body contains two different types of cells Somatic cells Reproduce by mitosis (asexual reproduction) They are diploid, that is they contain two complete sets of genetic information, (one from each parent) Gametes - PowerPoint PPT PresentationTRANSCRIPT
Mitosis
How Cells Reproduce
Types of Cells• The body contains two different types of
cells– Somatic cells
• Reproduce by mitosis (asexual reproduction)• They are diploid, that is they contain two complete
sets of genetic information, (one from each parent)
– Gametes• Reproduce by meiosis (sexual reproduction)• They are haploid. Contain only on set of genetic
information.
Mitosis
• Aged cell transforms itself into twin youthfu cells
• Happens millions of times every second in the human body.
• It gradually replaces every cell in your body except muscle and nerve cells
• In the body, what cells do you think replace themselves the fastest?
Fig. 9.3, p. 151
The Cell Cycle• The life of a cell can
be divided into recurring different time periods called the cell cycle.
• Two main parts to the cell cycle.– Interphase – mitosis
Fig. 9.3, p. 151
Interphase• The first part of
interphase is devided into 4 different parts
1. G12. S3. G24. Cytokinesis or the
division of the cytoplasm
Most cells spend most their time (90%) in interphase
Fig. 9.3, p. 151
in-text, p. 163
centromere
one chromosome(in duplicated state)
one chromatid
its sister chromatid
Mitosis
• The division of the nucleus is divided into four distinct phases
• Prophase• Metaphase• Anaphase• Telephase
Prophase
• Chromosomes start condensing• The spindle starts forming
– Centroles start to move to opposite ends of the cells– Microtubules extend out from the centrioles to the kinetochores
on each sister chromotid• Nuclear envelope begins to break apart
pair of centrioles microtubules
kinetochores
nucleus
plasmamembrane
pair of centrioles
cell chromosomes
nuclear envelope
microtubules
CELL AT INTERPHASE EARLY PROPHASE LATE PROPHASE PROMETAPHASE
Fig. 9.5a, p. 152
Metaphase
• Spindle fibers interact to orient chromatids and aligne them at the cell’s equator, halfway between the poles.
Anaphase
• The microtubules that are attached to the kinetochores begin to shorten and pull the sister chromotids apart.
• One half of each sister chromotide goes to each side of the cell
Telophase
• Telophase is the opposite of prophase– Nuclear envelope is
reformed– Microtubules are
wound up in the centrioles
– Chromosomes unwind into chromotine
Cytokinesis (The division of the cytoplasm)
• Contractile microfilaments at the cleavage furrow pull the plasma membrane inward.
• The membranes come together and pinch off to form new daughter cells
Questions
• How many DNA molecules are present in a duplicated chromosome?
• What is being separated in anaphase?
• What type of cells undergo mitosis?
• What is the chromosome number at G1? What is the chromosome number after cytokinesis?
METAPHASE ANAPHASE TELOPHASE INTERPHASE
Fig. 9.5b, p. 153
Meiosis
The Making of gametes
Meiosis
• Meiosis can be broken up into two different parts: Meiosis I and Meiosis II
• In meiosis the nucleus devides 2 times, once in meiosis I and again in meiosis II
• Meiosis I is broken up into four parts– Prophase I, Metaphase I, Anaphase I and telophase I
• Meiosis II also has four different stages.– Prophase I, Metaphase I, Anaphase I and telophase I
Prophase I
• The exact same steps that occur in prophase of mitosis occur here.
• There are additional steps– Synapsis: Homologous chromosomes come
together.– Crossing over takes place
Homologous chromosomes
• Homologous chromosomes are chromosomes that code for the same genes
• We inherit one homolog from each parent• There are 23 pairs of homologous
chromosomes in human somatic cells.
Fig. 10.4a p. 164
newly forming microtubules in the cytoplasm
PROPHASE IMEIOSIS I
Homologous Chomosomes come together in a process called synapsis
Crossing over
• During synapsis homologous chromosomes exchange segments of DNA in a process called Crossing over
Meiosis I
• In Meiosis I the cell is separating homologous chromosomes.
• In Meiosis II the cell is like mitosis in that the cell is separating sister chromotids
Fig. 10.4a p. 164
plasma membrane
newly forming microtubules in the cytoplasm
spindle equator (midway between the two poles)
one pair of homologous chromosomes
PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I
MEIOSIS I is separating homologous chromosomes
Fig. 10.4b p. 165
PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II
MEIOSIS II