Beginnings Chapter 3

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BeginningsChapter 3

• The Biological Basis of Development
• Slides by Jessica Mooneyham

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The Biological Basis of Development

• Chapter objectives
• How does fertilization, both natural and
  external, occur?
• What are the mechanisms of heredity and what
  could go wrong?
• What are the major features and anticipated uses
  of the Human Genome Project?

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The Fertilization Process

• The Beginnings
• In Vito fertilization occurs in the dish an
  external fertilization technique.

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The Fertilization Process

• The Sperm sperm(containing 23 chromosomes) are
  so tiny that estimates are the number of sperm
  equal to the worlds population could fit in a
  thimble. The major purpose of a males
  reproductive organs is to manufacture, store, and
  deliver sperm. The sperm has as its sole
  objective the delivery of its DNA to the egg.

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The Fertilization Process

• The Ovum(Egg)
• The egg is larger than the sperm, about the size
  of the period at the end of this sentence. The
  egg is round and its surface is about the
  consistency of stiff jelly. Eggs are usually
  fertilized about 12 hours after they are
  discharged form the surface of the ovary, or they
  die within 12 to 24 hours.

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The Fertilization Process

• The Menstrual Cycle
• The pituitary gland secretes a hormone that
  simulates the ripening of eggs, and after two
  weeks one egg, which has ripened more than the
  others, is discharged from the ovarys surface.
  The process called ovulation, triggers a chemical
  reaction that inhibits the ripening of further
  eggs.

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The Fertilization Process

• Implantation
• When the egg is discharged from the ovarys
  surface( a process called ovulation), it is
  enveloped by one of the fallopian tubes. Fusion
  of the two cells is quickly followed by the first
  cell division. As the fertilized egg, now called
  a zygote, travels toward implantation within the
  uterus, cell division continues. The cells
  multiply rapidly and after about seven days reach
  the uterine wall. The fertilized egg is now
  called a blastocyst.

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The Fertilization Process

• Twins
• Most twins occur when a womans ovaries release
  two ripened eggs(rather than one) and both are
  fertilized by separate sperm. These twins are
  called nonidentical, or dizygotic. Identical, or
  monozygotic, are twins whose genes are
  identical.Monozygotic twins are born with
  remarkable consistency, about 3 to 4 per thousand
  births, regardless of race.

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The Fertilization Process

• Causes of Infertility
• One in six American couples meet the criteria for
  infertility. In males, the number and quality of
  sperm are often suspected. Sexually transmitted
  diseases (STDs), especially Chlamydia (otherwise
  unknown unless detected by testing), may prevent
  conception. STDs may lead to pelvic inflammatory
  disease (PID), which may cause infertility.

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The Fertilization Process

• Assisted Reproductive Technologies (ARTs)
• in vitro fertilization
• artificial insemination by donor (AID) is the
  most widely used procedure.

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The Fertilization ProcessForms of Assisted
Reproduction Technologies

• In vitro fertilization-fertilization of egg with
  sperm occurs in a dish.
• Gamete intrafallopian transfer(GIFT)-sperm and
  egg are placed in the fallopian tube with the
  intent of achieving fertilization in a more
  natural environment( also known as embryo
  transfer).
• Zygote intrafallopian transfer(ZIFT)-the
  fertilized egg is transferred to the fallopian
  tube.

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The Fertilization ProcessForms of Assisted
Reproduction Technologies

• Sperm and egg donationmales and females either
  donate or sell their sperm and eggs.
• Cryopreservation-refers to freezing embryos for
  future use.
• Surrogate motherhood-one woman carries another
  womans embryo for nine months.

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The Fertilization Process

• Today a child may have as many as five parents
• A sperm donor (father or other male)
• An egg donor (mother or other female)
• A surrogate mother
• The couple who raises the child.

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The Fertilization Process

• Steps of In Vito Fertilization(IVF)
• The woman is usually treated with hormones and
  observed closely to determine the timing of
  ovulation.
• The physician makes an incision in the abdomen
  and insets a laparscope to remove mature eggs.
• The egg is placed in a solution containing blood
  serum and nutrients.

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The Fertilization Process

• Capacitation --- this is a process in which a
  layer surrounding the sperm is removed so that it
  can penetrate the egg.
• Sperm are added to the solution fertilization
  occurs.
• The fertilized egg is transferred to a fresh
  supporting solution.
• Fertilized eggs (usually there) are inserted into
  the uterus.
• The fertilized egg is implanted in the uterine
  lining.

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The Fertilization Process

• Adoption
• Closed adoption- Natural parents know nothing
  about the adopting parents
• Open adoption- Natural parents has considerable
  input into the adoption process.

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Heredity at Work

• meiosis, sex cell division, yields 23 chromosomes
• Somatic cell division, mitosis, 46 chromosomes,
  develops into muscles, tissue, bones, etc.

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Heredity at Work

• Are males more fragile?
• 160 males100 females conceived
• 105 males100 females are born

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Heredity at Work

• Chromosomes and Genes
• Structurally and functionally, females resist
  disease better than males.
• The male is more subject to hereditary disease
  and defect.
• Environmental elements expose males to greater
  hazards.
• Females are born with and retain a biological
  superiority over males.

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Heredity at Work

• Phenotypeobservable characteristics.
• Genotype-- Genetic composition

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Heredity at Work

• DNAStructure and function
• The DNA double helix. (a)The overall structure
  that gave DNA its famous name.(b)A closer
  examination reveals that the sides of the spiral
  are connected by chemicals similar to the rungs
  of a ladder.

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Heredity at Work

• Examine figure 3.6 and note how the strands
  intertwine. The strands ,similar to the sides of
  a ladder, are connected by chemical rings
  adenine (A), guanine (G), cytosine(C) and thymine
  (T).The letters are not randomly connected. A
  joins with T, G with C. If a code is written as
  AGCTTGA, it must appear as AGGTTGA or TCGAACT.

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Heredity at Work

• A remarkable feature of DNA is its ability to
  reproduce itself and insure that each daughter
  cell receives identical information. During
  mitosis, the DNA splits as readily as a person
  unzips a jacket (Curtis Barnes, 1997). Each
  single strand grows a new mate, A to T and G to
  C, until the double-helix model is reproduced in
  each daughter cell.

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Heredity at Work

• How Traits Are Transmitted
• Genes that control a particular trait, say for a
  cleft chin, can have alternate forms called
  alleles. If two alleles are identical (either for
  cleft or noncleft), the person is homozygous for
  the trait(cleft). If the alleles are different,
  then the organism is heterozygous.
• DominantThe tendency of a gene to be expressed
  in a trait.

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Heredity at Work

• Recessive---A gene whose trait is not expressed
  unless paired with another recessive genefor
  example, both parents contribute genes for blue
  eyes.
• MutationsAbrupt hereditary changes
• Polygenic inheritanceWhen many genes interact to
  produce a particular trait.

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Heredity at WorkExamples of Chromosomal Disorders

• Cytogenetics The study of chromosomes.
• Down syndrome is created by having one extra
  chromosome the individual may have 47
  chromosomes. This disorders causes distinctive
  characteristics such as, oval shaped eyes, thick
  tongues, small hands, mental retardation, heart
  defects, and an added risk of leukemia.

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Heredity at WorkHereditary Disorders

• Occasionally a male will possess an XXY pattern
  rather than the normal XY. This is called
  Klinefelter syndrome, a disorder that may cause
  small testicles, reduced body hair, possible
  infertility, and language impairment. Another
  pattern that appears in males is XYY, which may
  cause larger size and increased aggressionabout
  1 in 1,000 males birth.

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Heredity at WorkHereditary Disorders

• Females occasionally possess an XO pattern (lack
  of a chromosome) rather than XX. This is called
  Turner syndrome and is characterized by short
  stature, poorly developed secondary sex features
  (such as breast size), and usually sterility
  (about 1 in 2,500 female births).

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Heredity at Work

• Examples of Genetic Disorders
• Sickle-cell anemia, which mainly afflicts those
  of African descent, appeared thousands of years
  ago in equatorial Africa and increased resistance
  to malaria. Cystic fibrosis(CF) is the most
  severe genetic disease of childhood, affecting
  about 1 in 1,200 children. The CF gene now has
  been identified, however, and new research offers
  hope.Phenylketonuria(PKU) is an chromosomal
  disorder resulting in a failure of the body to
  break down the amino acid phenylalanine..

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Heredity at Work

• Examples of Genetic Disorders
• Spina bifida- (failure of the spinal column to
  close completely) is an example of a genetic
  defect caused by the interaction of several genes
  with possible environmental involvement. During
  the formation of the nervous system, if the
  developing neural tube does not close, spina
  bifida results, which can cause mental
  retardation. Pregnant women who take Folic Acid
  decrease their odds of having a child with this
  disorder.

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Sex Linked Inheritance

• Sex linked inheritance are characteristics
  associated with genes on the sex chromosomes. The
  X chromosome is three times larger than the Y
  chromosome. For a recessive trait to appear two
  recessive genes must be present. However on the
  23rd chromosome nothing on the Y chromosome will
  offset the effects of a gene located on the X
  chromosome.

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Examples of Genetic Disorders Cont.

• Perhaps the most widely known of these sex linked
  inheritance characteristics is hemophilia, a
  condition in which the blood of hemophiliacs does
  not clot properly.

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More Genetic Disorders

• In 1970, a condition called fragile X syndrome
  was discovered. In this disorder the end of the X
  chromosome looks ready to fall off, causing
  mental retardation in 80 of the cases. 1991, the
  gene for Fragile X was discovered and it appears
  that no physical problems will occur from this
  disorder. However (over time) the child will
  suffer from learning disabilities or mental
  retardation. This disorders occurs in about 1 in
  2,000 births.

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The Human Genome Project

• The Human Genome Project has been nothing less
  than an attempt to identify and map the 32,000
  genes that constitute our genetic makeup. By
  mapping the genes, crippling diseases have been
  located and pharmaceutical companies are now
  creating medicines to target and treat these
  diseases.

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The Human Genome Project

• How the Human Genome Project Began
• Two gatherings of Americas top biologist in the
  1980s are credited as the forerunners of the
  project.

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The Human Genome Project

• Ethical, Legal, and Social Implications
• Fairness in the use of genetic information
• Privacy and confidentiality of genetic
  information.
• Psychological impact

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The Human Genome Project

• Genetic testing
• Reproductive issues
• Clinical issues
• Commercialization