Beyond Mendel Genetic changes and Human heredity

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Beyond Mendel Genetic changes and Human heredity

• Last part of Chapter 11 and Chapter 12 for gifted
  book

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• 1905 E.B. Wilson and Nettie Stevens Americans
  studying insect chromosomes
• Saw that male insects always showed a
• chromosome that did not seem to have a match
  (females always had a perfect matching set of
  chromosomes.) Thus, they referred to the
  non-matching chromosomes as Sex Chromosomes.
• In females the sex chromosomes do match
• XX
• In males, one of the chromosomes looked as if it
  were missing a part, so called it a Y
• XY
• Punnett square for sex determination

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Gene 1909

• 1909 Wilhelm Johannsen Danish biologist who
  coined the term gene to define the physical
  units of heredity
• GENE segment of DNA molecules that carries the
  instructions for producing a specific trait

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Fruit Flies genetics guinea pig

• 1912 Thomas Hunt Morgan Showed evidence that
  the presence of white eye color in fruit flies
  was associated with a particular gene on a
  particular chromosome.

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• Normally, fruit flies always have RED eyes, but
  Morgan saw a white eyed one show up, and it was
  MALE!! Thought that this was strange, so he
  conducted an experiment
• P1 red eyed X
  red eyed
• F1 ¾ red eyed ¼ white
  eyed
• AND ALL OF THE WHITE EYED ONES WERE MALE!!!
• Determined that this was a sex-linked trait the
  trait for eye color in fruit flies is carried on
  the sex chromosome.
• Examples of other sex-linked traits
  hemophilia
• Color blindness
• C normal vision, c colorblindness
• X c Y crossed with XC Xc

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• Besides straight dominant and recessive genes,
  two other possibilities for combinations were
  proven
• Codominance when 2 alleles work together and
  BOTH are expressed without one masking the other
• Multiple Alleles when more than two
  possibilities for a trait are present.
• Example Blood type
• There are 3 alleles for blood type -- A, B, O
• Possible combinations
• AA, AO -- Type A blood
• BB, BO -- Type B blood
• AB -- Type AB blood
• OO -- Type O blood
• Here, A and B are dominant over O, but if A and
  B are present together, neither dominates!!!
  This is codominance they share the power of
  expression.

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Humans are difficult to study

• Why?
• of human genes is extremely large (each cell
  has 30,000 different genes)
• Humans cannot be easily controlled by an
  investigator
• Time span between generations is long
• Only a small of offspring are produced by each
  set of parents
• Environment has a HUGE effect on a persons
  development

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Have developed ways to approach the difficulties

• Pedigree analysis family history for a
  particular trait
• See page 315-316 for example
• Study of Genetic diseases
• Twin studies Nature vs. nurture
• Population Sampling
• Genetic Technology

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Figure 14.14 Pedigree analysis
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Figure 14.16 Large families provide excellent
case studies of human genetics
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Errors in chromosomes

• 1. Mistakes in numbers of chromosomes
• nondisjunction -- members of a pair of
  homologous chromos do not move apart properly
• ?result in offspring that have
• Aneuploidy abnormal chromo number
• Trisomy or Monosomy or Polyploidy

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Chromosome changes lead to new allele expression
problems

• 2. Mistakes in shape of chromos
• a. deletion part of chromo is broken off and
  lost completely
• b. duplication broken fragment of chromo
  attaches to sister chromatid so section is
  repeated on that chromatid
• c. inversion when fragment reattaches to
  original chromo but in reverse order
• d. translocation broken fragment attaches to
  a nonhomologous chromo
• (can exist as reciprocal or nonreciprocal)

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Figure 15.13 Alterations of chromosome structure
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Genetic Technology

• Carrier recognition with genetic screening and
  Fetal testing
• -ultrasound and sonograms
• -amniocentesis
• -fetoscopy
• -blood/urine tests of newborns

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Figure 14.17 Testing a fetus for genetic
disorders
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Figure 13.x3 Human female karyotype shown by
bright field G-banding of chromosomes
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Gene Therapy, Cloning, Pharmaceuticals

• Gene Therapy Inserting virus with DNA for
  allele into body Virus inserts (infects)
  patients DNA desired allele. Allele is read by
  bodys machinery and that trait is made can
  cure disease, repair body, etc
• Cloning creating an individual by skipping the
  step of mating Ind. Nucleus from somatic cell ?
  egg cell nucleus of another ? genetically
  identical ind.
• Pharmaceuticals Insulin Ex.