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15BT101-BIOLOGY FOR ENGINEERS

UNIT I
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Introduction

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Cell structure and function

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Genetic information, protein synthesis, and protein structure

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Cell metabolism

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Homoeostasis

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Cell growth, reproduction, and differentiation

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Introduction
A living organism is primarily physicochemical material that demonstrates a high degree of
complexity, is capable of self-regulation, possesses a metabolism, and perpetuates itself through time
...

Living substance is composed of a highly structured array of macromolecules, such as proteins, lipids,
nucleic acids, and polysaccharides, as well as smaller organic and inorganic molecules
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All reactions occurring within an individual living unit are called its metabolism
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FIVE KINGDOM CLASSIFICATION:
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Taxonomists utilize evolutionary
relationships in creating their groupings
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 All organisms belong to one of five major kingdoms
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 The five kingdoms are Monera, Protista, Fungi, Plantae, and Animalia
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Cell structure
Robert Hooke was the first scientist to describe cellular structure
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In 1673, Anton van Leeuwenhoek refined the grinding process to produce lenses that could be
used effectively in simple microscopes and was the first to view organism (living things)
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2

In 1839, Theodore Schwann concluded that all animals were made of cells
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CELL THEORY
The cell Theory was proposed by Theodore Schwann and Matthias Schleiden
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The cell is the unit of life
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All are arise from preexisting cells
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Prokaryotes
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In the nineteenth century, the cell was described merely as having a limiting outer
membrane, an interior nucleus, and a large mass of cytoplasm surrounding the nucleus
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These include ribosomes,
microtubules and microfilaments, flagella, cilia, and centrioles
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They lack cilia, centrioles, microfilaments, and microtubules
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In both prokaryotic and eukaryotic cells, a cell membrane (plasma membrane) is always
present
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It controls the passage of
materials into and out of the cell
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This sandwich structure
was indicated by electron microscope studies of many membranes
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Prokaryotes

3

Eukaryotes
Eukaryotic cells occur in all animals and plants, but there are a number of significant differences
between the cells of organisms in these two kingdoms
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Animal cells do not generally possess a cell wall
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Plastids are a
feature of most plant cells but are not found in the cells of animals
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While animal cells invariably demonstrate
a pair of centrioles lying just outside the nucleus, centrioles are not usually found in plants
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It controls the passage of materials into
and out of the cell
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This sandwich structure was indicated by electron microscope
studies of many membranes
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J
...
L
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 The fluid mosaic model better explains the dynamic nature of the membrane proteins
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According to this model, some lateral circulation of phospholipid and protein is
possible
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It is surrounded by a double
membrane, the nuclear membrane or envelope
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Since the outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum,
the pores may actually permit passage from the interior of the nucleus to the channels of the
endoplasmic reticulum
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These are dense bodies containing the
subunits for the ribosomes, the cytoplasmic organelles involved in the synthesis of protein
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It is usually attached to a specific chromosome in the nucleus
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The gene material of the cell is found in
the chromosomes
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These are dense bodies containing the
subunits for the ribosomes, the cytoplasmic organelles involved in the synthesis of protein
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It is usually attached to a
specific chromosome in the nucleus
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They lie just above the nuclear envelope (membrane),
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
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The microtubular structure of the centriole is the same as that of the basal body and may have
arisen from primitive basal bodies during cellular evolution
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CENTRIOLES

MITOCHONDRIA
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Mitochondria are rounded or cigar-shaped organelles that are particularly prominent in cells with
high metabolic activity
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Mitochondria have a double wall: an outer smooth membrane which forms the outer boundary
and an inner membrane which is extensively folded
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These enzymes are involved in the systematic degradation of organic molecules to yield energy
for the cell
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MITOCHONDRIA

6

ENDOPLASMIC RETICULUM
The endoplasmic reticulum (ER) is a series of membranous channels that traverse the cytoplasm of most
eukaryotic cells
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The endoplasmic reticulum serves many general functions, including the facilitation of protein folding
and the transport of synthesized proteins in sacs called cisternae
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In many parts of the cell, the endoplasmic reticulum is associated with small dense granules lying
along the outer border of its membrane
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They impart a
rough appearance to the endoplasmic reticulum, so that the ER is called the rough endoplasmic
reticulum (RER) in these regions, which are usually associated with active protein synthesis
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The ribosomes in the rough endoplasmic
reticulum do their job and create proteins which are then sent in to the rough endoplasmic
reticulum for advanced processing
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They may also be sent to the Golgi bodies for further advanced
processing, through vesicles
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It consists of tubules and vesicles that branch forming a network
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

The network of smooth endoplasmic reticulum allows increased surface area for the action or
storage of key enzymes and the products of these enzymes
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Calcium pumps serve to move the calcium
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One of the central tenets of biology, often referred to as the "central dogma," is that DNA
is used to make RNA, which, in turn, is used to make protein
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Ribosomes then
read the information in this RNA and use it to create proteins
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e
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Ribosomes do this by binding to an mRNA and using it as a template for the
correct sequence of amino acids in a particular protein
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Ribosomes are divided into
two subunits, one larger than the other
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GOLGI BODIES
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They exist as stacks of flattened sacs, or vesicles that are continuous with the channels of
the SER
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The outer portion of the Golgi apparatus releases its secretory material within membraneenclosed globules (secretory vesicles) that migrate to the surface of the cell
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The Golgi apparatus may actually be part of a dynamic system of membranous channels
within the cell in which all elements such as the nuclear envelope, the ER, the Golgi
apparatus, and the cell membrane are connected to each other without sharp boundaries
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Rupture of this membrane
releases these enzymes
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They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to
their role in autolysis
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 The vacuole may act as a reservoir for fluids and salts that might otherwise interfere with
metabolic processes occurring in the cytoplasm
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 Vacuoles containing digestive enzymes may also be formed around ingested food particles in a
variety of cells
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8

VACUOLES

CHLOROPLASTS
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Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct
photosynthesis
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Chloroplasts are observable as flat discs usually 2 to 10 micrometers in diameter and 1
micrometer thick
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The thylakoids are arranged in stacks called grana (singular: granum)
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Inside it is an empty area called the thylakoid space or
lumen
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CHLOROPLAST

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Cell metabolism
ATP: ENERGY FOR CELLS
Metabolism, synthesis, and active transport
ATP is consumed in the cell by energy-requiring (endothermic) processes and can be generated
by energy-releasing (exothermic) processes
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ATP is the main energy source for the majority of cellular functions
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ATP also plays a critical role in
the transport of macromolecules across cell membranes, e
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exocytosis and endocytosis
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Two types of metabolic reactions
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

Anabolism
Catabolism

Anabolism is the set of constructive metabolic processes where the energy released by
catabolism is used to synthesize complex molecules
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Anabolism involves
three basic stages
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Catabolism is the set of metabolic processes that break down large molecules
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The purpose of the catabolic reactions is to provide the
energy and components needed by anabolic reactions
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Organic molecules being used as a source
of energy in organotrophs, while lithotrophs use inorganic substrates and phototrophs capture sunlight as
chemical energy
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10

HOMEOSTASIS

Definition: Maintenance of the relative stability of the physical and chemical aspects of the
internal environment within a range compatible with cellular function
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Homeostasis has been studied most intensively in multicellular animals, particularly vertebrates
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Those processes that maintain homeostasis are known as
homeostatic mechanisms
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Positive feedback: a control system that causes the value of a physiological measurement to
change in the same direction as the initial deviation from set point
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The blood carries a great deal of the body heat
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CELL GROWTH, REPRODUCTION, AND DIFFERENTIATION
Most eukaryotic cells reproduce at a regular rate to produce new daughter cells that contain the
distributed materials of the original cell
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The apportionment of cytoplasm is called cytokinesis
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After cell division, each of the daughter cells begins the interphase of a new cycle
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Interphase
Before a cell can enter cell division, it needs to take in nutrients
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Interphase proceeds in three stages, G1, S, and G2
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Therefore, interphase is preceded by the previous cycle of mitosis and cytokinesis
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It is also called the growth phase
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This phase is marked by synthesis of various enzymes that are required in S phase, mainly those
needed for DNA replication
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S phase:
The ensuing S phase starts when DNA synthesis commences; when it is complete, all of the
chromosomes have been replicated, i
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, each chromosome has two (sister) chromatids
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Rates of RNA transcription and protein synthesis are very low during this phase
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G2 phase:
The cell then enters the G2 phase, which lasts until the cell enters mitosis
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Inhibition of protein synthesis during G2 phase prevents the cell from undergoing
mitosis
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The M phase has been broken
down into several distinct phases, sequentially known as:
 prophase
 metaphase
 anaphase
 telophase
 cytokinesis (strictly speaking, cytokinesis is not part of mitosis but is an event that directly
follows mitosis in which cytoplasm is divided into two daughter cells)
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus
into two identical sets in two nuclei
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Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle
- the division of the mother cell into two daughter cells, genetically identical to each other and to their
parent cell
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
...
The sequence of events is
divided into phases, corresponding to the completion of one set of activities and the start
of the next
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Cell cycle

BACTERIAL REPRODUCTION
Bacteria are prokaryotic organisms that reproduce asexually
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Binary fission results in the formation of
two bacterial cells that are genetically identical
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Cell Wall - Outer covering of the cell that protects the bacterial cell and gives it shape
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

Cell Membrane or Plasma Membrane - Surrounds the cell's cytoplasm and regulates the flow
of substances in and out of the cell
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Ribosomes - Cell structures responsible for protein production
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Nucleiod Region - Area of the cytoplasm that contains the single bacterial DNA molecule
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During binary fission, the single DNA molecule
replicates and both copies attach to the cell membrane
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Once the bacterium just
about doubles its original size, the cell membrane begins to pinch inward
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 Binary fission is a method of asexual reproduction by most prokaryotes
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It begins when the DNA of
the cell is replicated
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The cell elongates,
causing the two chromosomes to separate
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 Binary fission theoretically results in two identical cells
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This rapid rate of genetic change is what makes
bacteria capable of developing resistance to antibiotics and helps them exploit invasion
into a wide range of environments
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During conjugation, one bacterium connects itself to another through a protein tube structure called
a pilus
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Transformation
Some bacteria are capable of taking up DNA from their environment
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During transformation, the bacterium binds the DNA and
transports it across the bacterial cell membrane
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Transduction
Transduction is a type of recombination that involves the exchanging of bacterial DNA through
bacteriophages
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There are two types of transduction:
generalized and specialized transduction

Mitosis
Mitosis is the process during which the chromosomes are distributed evenly to two new cells that
arise from the parent cell undergoing division
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The two chromosomal strands (chromatids) are identical in their genetic
material and are joined at a constricted region called the centromere
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The kinetochores
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will play a significant role in the attachment of the spindle fibers to the chromosomes and
in the subsequent migration of the chromosomes
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8
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 In prophase, the relatively long first stage of division, the nuclear membrane breaks down
and the spindle forms
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Metaphase is characterized by the precise lineup of the chromosomes along the
equatorial plane
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Guided by the mooring spindle fiber,
one chromatid of each pair is moved to one pole, while the other chromatid is moved to
the opposite pole
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The nucleolus, which tended to disappear during prophase, begins to re-form at specific
nucleolar organizing regions of certain chromosomes
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Telophase may be regarded as a prophase run backwards
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Mitosis

16

MEIOSIS
A union of gametes in sexual reproduction always yields a doubling of the chromosome number
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’’ Meiosis probably evolved as a modification of mitosis and incorporates many of its
features
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The most dramatic difference occurs early in the
prophase when the homologous chromosomes mysteriously start to come together in pairs
synapsis
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Exchange of chromosome parts between the chromatids of two homologous chromosomes is
known as crossing over and results in the formation of hybrid chromosomes with mixed genetic
material
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These structures continue to be identified as tetrads,
since the homologues are still closely apposed to one another
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The total number of tetrads at the equator will be equal to the haploid (1n)
number
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Instead, whole
chromosomes separate, with one homologue moving to one pole and the other to the opposite
pole
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This first
division of meiosis is consequently called the reduction division
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A short stage called interkinesis occurs between telophase I and
17

prophase II
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The Second Meiotic Division
In the second meiotic division, called the equational division, a haploid set of replicate
chromosomes in each new cell migrates to the equatorial plane and lines up in a single line of
centromeres
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Each of the two cell products of meiosis I will produce two new cells, a total of four
haploid cells during the full meiotic process
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However, in the
apportionment of cytoplasm to the resultant cells and their modification, differences often arise
between the sexes
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Differentiation occurs numerous times
during the development of a multicellular organism as the organism changes from a simple
zygote to a complex system of tissues and cell types
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Differentiation dramatically changes a cell's size, shape,
membrane potential, metabolic activity, and responsiveness to signals
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With a few exceptions, cellular
differentiation almost never involves a change in the DNA sequence itself
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A cell that is able to differentiate into all cell types of the adult organism is known as
pluripotent
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A cell that is able to differentiate into all cell types, including the placental tissue, is
known as totipotent
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In cytopathology, the level of cellular differentiation is used as a measure of cancer progression
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