Chapter 4: Cell Division and Genetic Material
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GENETICS: is the field of biology that involves the study of how genetic information is passed from one
generation of organisms or cells to the next generation.
Understanding genetics begins with understanding cellular processes. The CELL THEORY states that:
o All living things are composed of one or more cells
o Cells are the smallest units of living organisms
o New cells come only from pre-existing cells by cell division
Traits must be passed from 1 cell, the parent cell, to new cells, the daughter cells.
Genetic information is passed on through DNA (Deoxyribonucleic acid). When a cell divides, each new cell
receives genetic information from the parent cell.
THE CELL CYCLE:
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Cells reproduce through controlled growth and division in a process called the cell cycle.
All SOMATIC CELLS which are the body cells of plants and animals that form the body of the organism,
and go through cell cycles. Somatic cells exclude the reproductive cells. Each time a cell undergoes one
complete cycle, it becomes two cells.
In multicellular organisms, there are 3 functions of cell division:
o Growth of an organism
o Repair of tissues and organs that have been damaged
o Maintenance to replace dying or dead cells
In most healthy, actively dividing animal cells, the cell cycle takes about 12-24 hours.
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Stages of the Cell Cycle:
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There are 3 main stages of the cell cycle: Interphase, Mitosis, and Cytokinesis.
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Interphase:
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Interphase is the stage during which a cell carries out its normal functions, grows, and makes copies of its
genetic material in preparation for the next stage of the cell cycle.
As the cell copies its DNA, it is preparing for division.
Interphase is divided into 3 phases: GI (Growth 1: is the phase of the major period of growth for a cell, the
cell is synthesizing new molecules in preparation for the next phase in the cell cycle); S (Synthesis: this is
when cellular DNA is copied, or replicated. During this phase, the DNA exists as uncondensed fibres called
chromatin); G2 (Growth 2: the cell synthesizes more molecules prior to mitosis and cell division).
Mitosis:
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Mitosis is the stage during which a cell’s nucleus and genetic material divides.
The cell’s copied genetic material separates and the cell prepares to split into two cells.
STAGE OF
MITOSIS
Prophase
WHAT OCCURS DURING THIS STAGE
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Metaphase
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Anaphase
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DIAGRAM
During prophase, the cell’s chromatin condenses into
CHROMOSOMES (a structure in the nucleus that contains
DNA). Because the DNA was copied during interphase, each
chromosome in prophase exists as two copies of one
chromosome.
The two chromosome arms are called SISTER CHROMATIDS
(two chromosomes that are genetically identical and are held
together at the CENTROMERE)
The nuclear membrane breaks down, and the nucleolus
disappears.
SPINDLE FIBRES (microtubule structures that facilitates the
movement of chromosomes within a cell) are formed from the
CENTROSOMES (a structure that helps to form the spindle
fibres) as they move apart to opposite poles of the cell.
Together, the fibres and centrosomes are called the spindle
apparatus, which moves and organizes the chromosomes
during mitosis.
The spindle fibres guide the chromosomes to the equator
(centre line) of the cell.
The spindle fibres from opposite poles attach to the
centromere of each chromosome.
Biologists consider each pair of sister chromatids to be a
single chromosome as long as the chromatids remain joined at
the centromere.
Each centromere splits apart, and the sister chromatids (now
chromosomes) separate from each other.
The spindle fibres shorten, pulling the chromosomes to
opposite poles of the cell.
At the end of anaphase, one complete set of chromosomes has
been gathered at each pole of the cell.
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Telophase
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Begins when the chromosomes have reached the opposite
poles of the cell.
The chromosomes start to unwind into stands of less-visible
chromatin.
The spindle fibres break down, and a nuclear membrane
forms around the new set of chromosomes.
A nucleolus forms within each new nucleus.
The Process of Mitosis
Cytokinesis:
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Mitosis is the process of nuclear division. It is followed by cytokinesis, which is the division of the
cytoplasm to complete the creation of two new daughter cells.
During cytokinesis in animal cells, an indentation forms in the cell membrane along the equator of the cell.
The indentation continues to deepen until the cell is pinched into two.
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In animal cells, cytokinesis is accomplished by means of microfilaments that constrict, or pinch, the
cytoplasm. Cytokinesis ends with the separation of the two genetically identical daughter cells. The
daughter cells are now in G1 of interphase.
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In plant cells, a new structure called a cell plate forms between the two daughter nuclei. Cell walls then
form on either side of the cell plate. Once the new cell wall is complete, two genetically identical plant cells
have formed.
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Prokaryotic cells do not have a nucleus. They complete cell division through binary fission. The DNA is
duplicated, both copies attach to the cell membrane, and the DNA molecules are pulled apart.
The Structure of Genetic Material
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DNA is made up of 2 long strands that forms a spiral shape called a double helix.
During most of the cell cycle, DNA exists as strands of chromatin fibre.
Once mitosis begins, the chromatin condenses into distinct chromosomes.
Nucleotides are the individual units of each strand of DNA. They are composed of a phosphate group, a
sugar group, and a base.
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The sugar and phosphate groups form the backbones of the two nucleotide strands. The bases protrude
inward at regular intervals.
The 4 bases in DNA are adenine (A), guanine (G), thymine (T), and cytosine (C).
Nucleotides are often identified by their bases. Each base is paired in a particular manner.
Adenine is paired with Thymine; Guanine is paired with Cytosine. These are called complimentary base
pairs.
A DNA mutation, or genetic mutation, is a change in the nucleotide sequence of DNA.
The complete DNA sequence in every cell of an organism is called the organism’s GENOME.
Making Exact Copies of DNA
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When DNA is replicated during interphase, the double helix unwinds and each strand of DNA serves as a
template for a new strand.
When DNA is copied, each of the new double-stranded DNA molecules contain one original strand of DNA
and one new strand of DNA. This is called semi-conservative since each new DNA molecule conserves half
of the original DNA.
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Chromosomes Are Paired
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Human somatic cells have 46 chromosomes. They are organized into 23 pairs of chromosomes.
For each pair, one chromosome is from the father, and the other chromosome is from the mother.
One chromosome pair is the sex chromosomes.
SEX CHROMOSOMES are an X or Y chromosome, which determines the genetic sex of an organism.
o A human female has two X chromosomes
o A human male has one Y chromosome and one X chromosome.
o The sex chromosomes are always counted as a pair.
The remaining 22 pairs of chromosomes are called autosomes.
AUTOSOMES are a chromosome that is not involved in determining the sex of an organism.
Chromosomes are paired based on sharing similar characteristics.
o Homologous Chromosomes Contain Alleles
o HOMOLOGOUS CHROMOSOMES are pairs of chromosomes that appear similar, in terms of
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their length, centromere location, and banding pattern when stained with certain dyes. However,
they are not identical to one another.
GENES are sections of DNA that contain genetic information for the inheritance of specific traits.
Homologous chromosomes carry genes for the same traits (such as hair colour). However, they can
carry different forms of the same gene, called ALLELES.
o Examining Chromosomes: The Karyotype
o The particular set of chromosomes that an individual has is called the person’s KARYOTYPE.
o To prepare a karyotype, a cell sample is collected and stained, which produces a banding pattern on
the chromosomes. Then, the chromosomes are sorted and paired. The autosomes are numbered 122 and the sex chromosomes are labeled as X or Y. The Y chromosome is much smaller than the X
chromosome.
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SEXUAL REPRODUCTION
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ASEXUAL REPRODUCTION is reproduction that requires only 1 parent and lead to the production of
genetically identical offspring. If mitosis were the only stage for reproducing cells, we would produce exact
clones of ourselves during reproduction.
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SEXUAL REPRODUCTION is reproduction that involves 2 parents and leads to the production of
genetically distinct offspring.
Haploid and Diploid Cells in Sexual Reproduction
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Sexual reproduction involves the fusion of a male reproductive cell (sperm) with a female reproductive cell
(egg). These reproductive cells are called GAMETES, and the cell that results from this fusion is called a
ZYGOTE. The process of combining gametes to form a zygote is called FERTILIZATION.
When gamete cells fuse during fertilization, the resulting zygote has the same number of chromosomes as
the somatic cells for that organism. This means that the gametes must therefore only have half the number
of chromosomes as the parent cells.
Gametes, which contain single, unpaired chromosomes, are called a haploid. A HAPLOID is a cell that
contains half the number of chromosomes as the parent cell. The haploid number of chromosomes is
designated as n. Each human gamete is haploid, with n = 23.
Cells that contain pairs of chromosomes, which include all somatic cells, are said to be diploid. A DIPLOID
is a cell that contains pairs of homologous chromosomes.
After fertilization, the zygote cell is diploid, with a total of 2n chromosomes. This means that n
chromosomes are from the female parent, plus n chromosomes are from the male parent. Therefore, the
diploid number in humans is 46.
Remember, the n also describes the number of pairs of chromosomes in an organism. When 2 human
gametes combine, 23 pairs of homologous chromosomes are formed.
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Meiosis – Producing Haploid Gametes
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MEIOSIS is the cellular process that produces cells containing half the number of chromosomes as the
parent cell. Meiosis produces gametes with a haploid number of chromosomes.
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Meiosis has 2 key outcomes:
o Genetic Reduction: Meiosis is a form of cell division that produces daughter cells with half the
number of chromosomes of the parent cell.
o Genetic Recombination: The products of meiosis have different combinations of alleles. This gives
rise to offspring that are genetically different from one another and their parents. This greatly
increases the genetic variation in a population.
o Interphase:
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Cells that divide by meiosis proceed through the growth and synthesis phase of interphase before
dividing.
This includes the replication of chromosomes. So, at the start of meiosis, a cell contains duplicated
chromosomes. Each chromosome is made up of a pair of identical sister chromatids held together
at the centromere.
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o Phases of Meiosis:
Meiosis I
STAGE OF MEIOSIS I
Prophase I
WHAT OCCURS DURING THIS STAGE
- Each pair of homologous chromosomes (1 chromosome from each
parent) lines up side by side.
-This aligning of homologous chromosomes is called SYNAPYSIS and the
chromosomes are held together along their lengths.
-While they are lined up, segments of the chromosomes may be exchanged.
This is when genetic diversity occurs.
-The centrosomes move to the poles of the cell and the spindle apparatus
forms.
Metaphase I
-The pairs of homologous chromosomes line up along the equator of the
cell.
-The spindle fibres attach to the centromere of each homologous
chromosome.
Anaphase I
-The homologous chromosomes separate and move to opposite poles of the
cell.
-Since the sister chromatids are still held together, the centromeres do no
split as they do during mitosis. Therefore, a single chromosome (made up
of 2 chromatids) from each homologous pair moves to each pole of the cell.
-The chromosome number is reduced from 2n (diploid) to n (haploid).
Telophase I
-The homologous chromosomes begin to uncoil and the spindle fibres
disappear.
-Cytokinesis occurs. This involves a nuclear membrane forming around
each group of homologous chromosomes, and two cells form.
-Each of these new cells is now haploid.
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*** Chiasmata: The point where two homologous non-sister chromatids exchange genetic material during chromosomal
crossover during meiosis.
*** Tetrad: Is made up of four chromatids or two pairs of sister chromatids.
*** Kinetochore: A protein structure on chromatids where the spindle fibres attach during cell division to pull sister chromatids
apart.
Meiosis II
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The phases of meiosis II are similar to the phases of mitosis.
The key difference is that the cell that undergoes division during meiosis II is haploid instead of diploid.
A haploid number of chromosomes line up at the equator during metaphase II.
During anaphase II, the sister chromatids are pulled apart at the centromere by the spindle fibres. The
chromosomes move toward the opposite poles of the cell.
The chromosomes reach the poles during telophase II, and the nuclear membrane and nuclei reform.
At the end of meiosis II, cytokinesis occurs, resulting in 4 haploid cells, each with n number of chromosomes.
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A Comparison of Mitosis and Meiosis
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Mitosis consists of only one set of division phases and produces two diploid daughter cells that are
identical.
Meiosis consists of two sets of divisions and produces four haploid daughter cells that are not identical.
Meiosis is important for organisms, such as humans, because it results in genetic variation.
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Gamete Formation in Animals
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The products of meiosis are haploid gametes.
In humans, the gametes are sperm and eggs.
The process of producing male gametes (sperm) is called SPERMATOGENESIS. In spermatogenesis, four
haploid sperm cells form from one diploid cell.
o In most male animals, meiosis occurs in the testes.
o The process of spermatogenesis starts with a diploid cell called a spermatogonium.
o Beginning at puberty, spermatogonia reproduce by mitosis, and the resulting cells undergo meiosis
to form 4 haploid cells.
o Following meiosis II, the cells undergo a final set of developmental stages to develop into mature
sperm.
o The nucleus and certain molecules required by the cell are organized into a “head” region.
o The mid-section holds many mitochondria, which are an energy resource for the cell.
o Finally, a long tail-like flagellum develops for locomotion.
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The process of producing female gametes (eggs) is called OOGENESIS.
o In most female animals, meiosis takes place in the ovaries.
o Oogenesis starts with a diploid cell called an oogonium.
o Before birth, the oogonia reproduce by mitosis, and they begin meiosis, but stop at prophase I.
o Meiosis I will continue for one cell each month, beginning at puberty.
o Oogenesis involves the unequal division of cytoplasm. The cell that receives the most of the
cytoplasm after the first division continues through meiosis I and II to form a viable egg.
o This cell contains a large amount of nutrients that will support the zygote after fertilization.
o The other, smaller cell formed, is called a polar body. The polar body will degenerate.
o The final stages of meiosis II are not completed unless fertilization by a sperm cell occurs.
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Multiple Births
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A woman can give birth to more than one baby at once.
This occurs when more than 1 egg is released. If 2 eggs are released and both are fertilized, fraternal (nonidentical) twins are born.
However, if a single zygote divides into two separate bodies in the first few days of development, identical
twins will be born.
The Importance of Meiosis for Genetic Variation
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The outcome of meiosis is the formation of genetically distinct haploid gametes.
Remember that each diploid cell has two copies of each chromosome. One copy of this homologous pair
was contributed by the female gamete (egg), so it is of maternal origin. The other chromosome was
contributed by the male gamete (sperm), so it is of paternal origin.
During meiosis, genetic variation is ensured in two ways:
A) the creation of gametes that carry different combinations of maternal and paternal
chromosomes, in a process called INDEPENDENT ASSORTMENT. During metaphase I,
chromosomes are arranged in homologous pairs along the equator of the cell. In each pair, the
chromosome of maternal origin is oriented toward one pole of the cell, and the chromosome of
paternal origin is oriented toward the other pole. This orientation of each pair of chromosomes is
independent of the orientation of the other pairs. The number of genetically distinct gametes that
can be produced from a diploid cell is 2n, where n is the number of chromosome pairs in the diploid
cell. Each human, with 23 pairs of chromosomes, can therefore produce 223, or 8 388 608
genetically distinct gametes.
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By the exchange of genetic material between maternal and paternal chromosomes, in a process
called CROSSING OVER. Crossing over is the exchange of chromosomal segments between a pair
of homologous chromosomes. While homologous chromosomes are lined up during prophase I,
non-sister chromatids of homologous chromosomes may exchange pieces of chromosome. Crossing
over can occur at several points along non-sister chromatids. A section of chromosome that is
crossed over may contain hundreds, or thousands, of genes. As a result of crossing over, individual
chromosomes contain some genes of maternal origin and some genes of paternal origin.
Errors During Meiosis
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Many errors that occur during meiosis produce gametes that cannot survive.
However, some gametes do survive. Since every cell in an offspring is produced from the one zygote cell, all
of the cells in the offspring will contain the error.
There are two types of chromosomal errors that can occur during meiosis: changes in chromosome
structure, and changes to chromosome number
A) Errors Caused by Changes in Chromosome Structure
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During crossing over, the chemical bonds that hold the DNA together in the chromosome are broken
and reformed. Sometimes, the chromosomes do not reform correctly.
Also, non-homologous pairs may cross over, producing chromosomes that contain genes not
normally on that chromosome.
Errors to chromosome structure include:
o Deletion:
A piece of a chromosome is deleted.
o Duplication:
A section of a chromosome appears two or more times in a row.
o Inversion:
A section of a chromosome is inverted.
o Translocation:
A segment of one chromosome becomes attached to a different
chromosome.
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Error in Chromosome
Structure
Deletion
Example of Genetic Disorder
Cri du Chat
-A syndrome is caused by a deletion in chromosome 5.
-Children with this syndrome cry with a high-pitched, catlike sound.
-Other symptoms include: low birth weight, widely spaced eyes, recessed
chin, and developmental and cognitive delays.
Duplication
Charcot-Marie-Tooth Disease
-Most cases are caused by a duplication of a gene on chromosome 17.
-Common symptoms include: muscle weakness and loss of sensation in
the lower legs, feet, and hands.
-A high foot arch with constantly flexed toes.
Inversion
FG Syndrome
-It is caused by the inversion of a section of the X chromosome.
-It is almost always in males.
-Symptoms include: intellectual disabilities, delayed motor development,
low muscle tone, and broad toes and thumbs.
Translocation
Chronic Myelogenous Leukemia (CML)
-It is a cancer of the white blood cells, and is caused by a translocation
between chromosome 9 and 22. This results in the formation of an
abnormal gene.
-Treatment includes using a drug that stops the increased production of
white blood cells.
Errors Caused by Changes in Chromosome Number
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Sometimes homologous chromosome pairs or sister chromatids do not separate as they should during
meiosis. This is called NON-DISJUNCTION. It can occur in anaphase I or II of meiosis.
In anaphase I, non-disjunction occurs when homologous chromosome pairs do not separate to opposite
poles. Instead, one entire pair is pulled toward the same pole.
In anaphase II, non-disjunction occurs when sister chromatids do not separate to opposite poles. Both
sister chromatids are pulled toward the same pole.
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As a result, non-disjunction produces gametes that have too few or too many chromosomes.
Genetic Disorders Associated with Chromosome Number
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Many genetic disorders are due to an individual having an incorrect number of chromosomes.
For example) Down syndrome. Individuals are born with an extra chromosome or an extra-piece of
chromosome 21.
The incident of non-disjunction leading to Down syndrome increases with maternal age. At the age of 49, a
woman has a 1 in 11 chance of having a child with Down syndrome; but only a 1 in 1490 chance at the age
of 20.
Trisomies and Monosomies
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MONOSOMY is a condition in which one chromosome is lost due to non-disjunction. A gamete is missing
one chromosome of a homologous pair. For example) Turner Syndrome involves missing an X
chromosome. Individuals with this disorder have female sexual characteristics that are underdeveloped.
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TRISOMY is a condition in which there is a gain of an extra chromosome due to non-disjunction. The most
common trisomies are found in chromosomes 21, 18, and 13, and in abnormalities in the number of sex
chromosomes.
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Conditions
Chromosomal Abnormalities in Humans
Number of Live
Syndrome
Characteristics
Births
Autosome
Trisomy 21
1 in 800
Down
Trisomy 18
1 in 18 000
Edward
Trisomy 13
1 in 15 000
Patau
XXY
1 in 1000 males
Klinefelter
XYY
1 in 1000 males
Jacobs
XXX
1 in 1500 females
Triple X
XO
(1 X chromosome, only)
1 in 5000 females
Turner
Intellectual disabilities, abnormal
pattern of palm creases, almondshaped eyes, flattened face, short
stature.
Intellectual and physical disablitites,
facial abnormalities, extreme muscle
tone, early death.
Intellectual and physical disabilities,
wide variety of defects in organs,
large triangular nose, early death.
Sex Chromosome
Sexual immaturity (inability to
produce sperm), breast swelling.
Typically no unusual symptoms; some
individuals may be taller than
average.
Tall and thin, menstrual irregularity.
Short stature, webbed neck, sexually
underdeveloped.
Prenatal Genetic Testing
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Prenatal genetic testing refers to tests performed on a fetus that are based on testing for genetic-based
abnormalities. In Canada, genetic testing is covered by OHIP and all pregnant women are permitted to
have these tests done.
Some ethical issued related to prenatal genetic testing includes pregnancy termination and potential
discrimination against persons with disabilities.
Prenatal Testing Procedures
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Typically, prenatal testing initially involves the expectant mother having blood tests and an ultrasound.
These tests can provide information about potential physical and chromosomal abnormalities, and indicate
whether there is a high risk for genetic problems.
Invasive tests involve collecting a DNA sample of the fetus.
o Amniocentesis: A sample of amniotic fluid, which contains fetal cells, is taken after the 14th week of
pregnancy. It is taken using a needle that is inserted through the stomach into the amniotic fluid.
o Chorionic Villus Sampling (CVS): A sample of cells from the chorion (part of the placenta) is taken
after the 9th week of pregnancy. A catheter is inserted through the cervix, into the amniotic fluid.
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REPRODUCTIVE STRATEGIES AND TECHNOLOGIES
Reproductive Strategies in Agriculture
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SELECTIVE BREEDING is the process of breeding plants and animals for desirable traits.
ARTIFICIAL INSEMINATION is the artificial transfer of semen into a female’s reproductive tract.
A benefit of artificial insemination is that semen from high-quality males is widely available,
through breeders and on-line sources.
o It allows farmers and pet owners to choose desirable traits.
EMBRYO TRANSFER is the process by which an egg that has been fertilized artificially is transferred into
a recipient female’s uterus.
o Embryos can be shipped very easily, so farmers do not need to physically ship the animal. This is a
benefit since studies show that animals born and raised in their native environment do better than
those that are imported.
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Reproductive Technologies for Humans
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A technique that is used to help couples conceive a child is referred to as Assisted Reproductive
Technology (ART).
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Artificial insemination is also used in humans. The sperm is collected and concentrated, then introduced
into the women’s vagina. The donor sperm can be from the woman’s male partner, or from an unknown
source, such as a sperm bank.
IN VITRO FERTILIZATION (IVF) is a technique used to fertilize egg cells outside the female’s body.
o It is often used for women who have blocked fallopian tubes.
o Immature eggs are retrieved from the woman. The eggs are combined with sperm in laboratory
glassware. After fertilization, the developing embryo is placed in the uterus.
o Since fertilization occurs in a laboratory, babies conceived using this method are referred to as
“test-tube babies”.
o Since 1978, over 1.5 million babies have been conceived using this method.
Pre-implantation Genetic Diagnosis
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Parents with a history of genetic disorders in their family may choose to use a process that allows for the
diagnosis of genetic disorders soon after fertilization. IVF is used in this case.
Since the genetic testing is done before the embryo is implanted in the uterus, the process is called preimplantation genetic diagnosis (PGD).
Parents of a sick child have also used PGD to genetically match another sibling. A genetic match means that
the newborn sibling is able to donate umbilical cord blood, which contains stem cells that can be used to
treat a number of diseases.
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Cloning: Reproduction of Exact Copies
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CLONING is the process that produces identical copies of genes, cells, or organisms.
o Gene Cloning:
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GENE CLONING is the use of DNA manipulation techniques to produce multiple copies of a single
gene or segment of DNA in a foreign cell.
For example) Insulin (a hormone that enables the body to use sugar) is absent in people with type I
diabetes. Before gene cloning, people with diabetes used purified insulin from animal sources. It
was a labour-intensive and expensive process. However, since the 1980’s, human insulin has been
produced in bacteria through cloning of the insulin gene.
o Therapeutic Cloning and Reproductive Cloning:
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THERAPEUTIC CLONING involves producing identical cells that are used to treat various
diseases. It is the process of replacing an egg cell’s nucleus with the nucleus from a somatic donor
cell to produce a cell line of genetically identical cells. This includes using the cloned cells to grow
new tissues and organs.
REPRODUCTIVE CLONING involves production of cell clones, but with the aim of producing a
genetically identical organism.
Unlike gene cloning, therapeutic cloning and reproductive cloning are surrounded by controversy
because there are ethical questions about how they are used.
Both use a process called somatic cell nuclear transfer (SCNT) to generate the cloned cells. In this
technique, an egg cell’s nucleus is removed and replaced with the nucleus of a somatic cell of a
donor.
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o Reproductive Cloning in Animals:
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Reproductive cloning in animals is not very successful. The birth rate ranges from only 0.5 to 6%.
As well, cloned offspring tend to have high mortality rates, as well as high incidences of disease and
premature ageing.
Regardless, research into animal cloning continues because of the potential benefit. Animal cloning
could be used to repopulate an endangered species.
Therapeutic Cloning and Stem Cells
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STEM CELLS are undifferentiated (unspecialized) cells that can develop and become specialized into
different cell types of the body. Under the right conditions, stem cells can develop into any one of more
than over 200 types of somatic cells.
Controversy is due to the initial use of embryos as a source of stem cells.
Over the years, scientists have used 3 different sources for stem cells:
o Embryonic stem cells: They are obtained from embryos
o Adult stem cells: They are somatic cells that have retained the ability to differentiate into some
other cell types.
o Induced pluripotent stem cells: They are specialized adult stem cells that have been induced to
return to a stem-cell like state. This choice has decreased the reliance on using embryonic stem
cells.
Successes in stem cell research includes:
o Improving heart function and formation of blood vessels by injecting stem cells into the circulatory
systems of animals.
o Starting with stem cells, scientists have “grown” blood vessels, heart valves, skin, and urinary
bladders.
o Stem cell research holds great promise for regenerative medicine – the creation of tissues and
organs to replace those damaged or lost due to age, disease, trauma, or genetic defects. Since the
stem cells are generated from a patient’s own somatic cells, they are a genetic match to the patient.
This means that they are unlikely to be rejected by the immune system.
Transgenic Organisms
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Transgenic organisms are organisms whose genetic material includes DNA from a different species.
In general, transgenic organisms have had a sequence of their genome altered for a specific purpose.
Transgenic crop plants account for over half the corn and canola grown in North America. Many have been
modified to increase their resistance to herbicides, insects, pests, and viruses.
A great promise of plant genetic engineering is the production of plants with increased nutritional value. In
developing countries where rice is a staple food, symptoms of iron and vitamin A deficiencies affect many
people. Therefore, genetically modified strains of rice now contain both iron and vitamin A. It is called
golden rice.
Transgenic plants can also be used for medical purposes. The human insulin gene has been inserted into a
safflower plant. Insulin can grow in the plant, making insulin much less expensive.
Transgenic animals can serve as organ donors for humans. However, it is still very difficult.
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