The Cellular Basis of Inheritance

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Unit 5 The Cellular Basis of Inheritance
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I. All Cells come from Cells A. Repair and
Growth 1. Underneath the surface layer are
living cells that are engaged in a vital
activity reproducing. The new cells
gradually move outward toward the skins
surface, replacing dead cells that have rubbed
off.
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2. Another important role that cell reproduction
plays in is growth - simply increasing in size
from a baby to a child to an adult. All of the
trillions of cells in your body result from cell
reproduction, a series of cell divisions that
began with a single fertilized egg.
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Figure 9-1Cell reproduction enables your body to
produce new skin cells that replace dead cells at
your skin's surface.
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B. Reproduction 1. Asexual Reproduction-
process in which a single cell or set of cells
produces offspring that inherit all their
genetic material from one parent make a copy
of themselves a) Example Single-celled
organisms (Paramecium)
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2. Sexual Reproduction-process in which genetic
material from two parents (egg and sperm)
combines and produces offspring that differ
genetically from either parent
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II. The cell cycle multiplies cells A.
Chromosomes and Cell Division 1.
Chromatin-combination of DNA and protein
molecules, in the form of long, thin fibers,
making up the genetic material in the
nucleus of a eukaryotic cell
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2. Chromosomes- condensed threads of genetic
material formed from chromatin as a cell prepares
to divide a) The human body contains 46
chromosomes in each body or somatic cell.
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b) Before cell division begins, a cell duplicates
or copies all of its chromosomes. Each
chromosome now consists of two identical joined
copies called sister chromatids. The region
where the two chromatids are joined tightly
together is called the centromere.
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B. The Cell Cycle 1. The sequence of events from
production of a eukaryotic cell to the time the
cell itself reproduces. 2. Stages a)
Interphase- the stage of the cell cycle during
which a cell carries out is metabolic processes
and performs its functions
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1) During the G1 phase of Interphase, the cell
grows. 2) One key event in Interphase is the
duplication of the DNA in the cells
chromosomes. This period is called the S
phase. 3) During the G2 phase, the cell
prepares to divide.
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b) Mitotic phase- the stage of the cell cycle
when the cell is actually dividing 1) During
mitosis, the nucleus and the duplicated
chromosomes divide and are evenly distributed,
forming two daughter nuclei.
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2) Cytokinesis is the process by which the
cytoplasm is divided in two. This stage
usually begins when mitosis is completed. 3)
The combination of mitosis and cytokinesis
produces two genetically identical daughter
cells since the chromosomes were duplicated.
Each daughter cell has a single nucleus, some
surrounding cytoplasm, and a cell membrane.
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III. Cells divide during the Mitotic phase A.
The Mitosis Dance 1. During mitosis, the
chromosomes movements are guided by a
framework of microtubules called the spindle.
These microtubules grow from two centrosomes
(centrioles).
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2. Stages of Mitosis a) Prophase 1) In the
first stage, the chromosomes have condensed
and are thick enough to be seen. 2) The
nucleolus disappears and the cell stops making
ribosomes. 3) The nuclear envelope breaks
down. 4) In the cytoplasm, the spindles
forms. The chromosomes attach to the
spindle.
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Spindles forming
Centrosomes
Nuclear Envelope disappears
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b) Metaphase 1) The chromosomes line up across
the middle of the cell. The chromosomes are
attached to the spindles.
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c) Anaphase 1) The sister chromatids separate
from their partners. 2) Proteins at the
centromeres help move the chromosomes toward the
poles.
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d) Telophase and Cytokinesis 1) The spindle
disappears, two nuclear envelopes reform (one
around each set of daughter chromosomes), the
chromosomes uncoil and lengthen, and the
nucleoli reappear. 2) Cytokinesis completes
cell division by dividing the cytoplasm into 2
daughter cells, each with a nucleus.
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Nucleolus returns
Chromosomes uncoiling
Nuclear envelope forming
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B. Cytokinesis in Animals and Plants 1. In
animal cells, the first sign of cytokinesis is
an indentation around the middle of the
cell. a) This indentation is caused by a
ring of microfilaments in the cytoplasm just
under the cell membrane.
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b) The ring contracts, deepening the
indentation and pinching the parent cell in
two. 2. In plant cells, a disk containing a cell
plate forms inside the cell and grows outward.
Eventually this new piece of cell wall divides
into two.
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IV. Cancer cells grow and divide out of
control A. Tumors and Cancer 1. Out-of-control
cell reproduction can produce a mass of cells
called a tumor. 2. Benign tumor- an
abnormal mass of normal cells may cause health
problems can be removed by surgery stay in
one spot
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3. Malignant tumor- masses of cells that result
from the reproduction of cancer cells 4. Cancer
is a disease caused by the severe disruption of
the mechanism that normally control the cell
cycle a) The most dangerous characteristic
of cancer cells is their ability to
spread b) Metastasis- the spread of cancer
beyond their original site
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Figure 9-11Cells in a cancerous tumor reproduce
at an abnormally fast rate and become irregular
in appearance. When individual cells metastasize
(travel from the original tumor), the cancer can
spread.
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B. Cancer Treatment 1. Malignant tumors are
removed by surgery. However, it is difficult to
successfully remove all traces of cancer with
surgery, so doctors will use radiation therapy
or chemotherapy. a) In radiation therapy, the
parts of the body with cancerous tumors are
exposed to radiation, which disrupts cell
division.
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b) Chemotherapy involves treating the patient
with drugs that disrupt cell division. c) Both
radiation and chemotherapy have side effects
sterility, nausea, and hair loss.
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V. Meiosis functions in Sexual reproduction A.
Homologous Chromosomes 1. Meiosis- type of
cell division that produces four cells, each
with half as many chromosomes as the parent
cell a) Occurs in the cells of the sex
organs (sperm and eggs).
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2. Karyotype- a display of a persons 46
chromosomes a) Homologous chromosomes- one of a
matching pair of chromosomes, one inherited
from each parent
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1) Each homologous chromosome in a pair carries
the same sequence of genes controlling the same
characteristics. 2) Humans have 23 homologous
pairs of chromosomes. a) The 23rd pair of
chromosomes in a karyotype are the sex
chromosomes. Female sex chromosomes are 2 X
chromosomes (they look alike). Male sex
chromosomes are X and Y (they do not look
alike).
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B. Diploid and Haploid Cells 1. Almost all
human cells are diploid that is, they contain
two homologous sets of chromosomes (humans have
46 or 2n). 2. The exceptions are egg and sperm
cells, known as sex cells or gametes. Each
gamete has a single set of chromosomes and is
called haploid (gametes have 23 or n).
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3. Fertilization- the fusion of the nuclei and
cytoplasm of a sperm and egg cell forming a
diploid zygote a) zygote- a diploid cell formed
when the nucleus of a sperm fuses with the
nucleus of an egg
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C. The Process of Meiosis 1.
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2. Stages of Meiosis I (Homologous chromosomes
are separated) a) Prophase I 1) Proteins
cause homologous chromosomes to stick
together. a) The paired chromosomes, now
consisting of 4 chromosomes, are called
tetrads. They attach to the spindle.
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2) The sister chromatids in the tetrads may
exchange some genetic material in a process
called crossing over.
Centrosomes
Spindles
Crossing over
Tetrad
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b) Metaphase I 1) The tetrads move to the middle
of the cell and line up across the spindle.
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c) Anaphase I 1) Homologous chromosomes separate
as they move to opposite poles.
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d) Telophase I and Cytokinesis 1) The
chromosomes arrive at the poles. a) Each pole
now has a haploid daughter nucleus because it
has only one set of chromosomes. 2)
Cytokinesis creates two haploid daughter cells.
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Nuclear envelope reforms
Cell dividing
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3. Stages of Meiosis II (sister chromatids are
separated) a) Prophase II 1) In each haploid
daughter cell, a spindle forms, attaches to the
centromeres, and moves the individual
chromosomes to the middle of the cell.
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b) Metaphase II 1) The chromosomes line up in
the middle of the cell with spindles attached
to each sister chromatid.
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c) Anaphase II 1) The sister chromatids separate
and move to opposite poles.
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d) Telophase II and Cytokinesis 1) The
chromatids arrive at the poles. 2) Cytokinesis
splits the cells one more time. 3) Four
haploid daughter cells are produced.
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Nucleolus returns
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VI. Meiosis increases genetic variation among
offspring A. Assortments of Chromosomes 1.
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2. For a human, n23, so there are 223, or about
8 million possible chromosome combinations.
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B. Crossing Over 1. Crossing over is the
exchange of genetic material between homologous
chromosomes. 2. Genetic recombination- new
combination of genetic information in a gamete
as a result of crossing over during prophase I
of meiosis
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C. Review Comparison of Mitosis and Meiosis 1.
In both mitosis and meiosis, the chromosomes
duplicate only once. a) Mitosis involves one
division of the genetic material in the nucleus
and produces two diploid cells. b) Meiosis
involves two nuclear divisions producing 4
haploid cells.
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Overview of Mitosis
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Overview of Meiosis