Rules of probability

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Chapter 14 Highlights

• Rules of probability
• 1. Rule of multiplication
• a. how do we determine the chance that two
  or more independent events will occur
  together in a specific combination?
• b. compute probability for each event then
  multiply independent probabililities to
  obtain the overall probability
• 2. Rule of addition
• a. a. used to find the probabilility of an
  event that can occur in two or more
  different ways is the sum of the
  separate probabilities of those ways

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Example TtRr X TtRr

• The probability of getting a tall offspring is ¾.
• The probability of getting a red offspring is ¾.
• The probability of getting a tall red offspring
  is ¾ x ¾ 9/16

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Comment

• Use the Product Rule to calculate the results of
  complex crosses rather than work out the Punnett
  Squares.
• Ex TtrrGG X TtRrgg
• What is the probability that you would get a Tall
  plant with Wrinkled (dom) Green seeds?

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Solution

• What is the probability that you would get a Tall
  plant with Wrinkled (dom) Green seeds?
• Ts Tt X Tt
• Rs rr X Rr
• Gs GG x gg
• Product is

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3. Rules can be combined a. Trihybrid cross
PpYyRr x Ppyyrr What is the probability
that offspring will exhibit recessive
phenotypes for at least two of the 3 traits?
Possibilities ppyyRr, ppYyrr, Ppyyrr,
PPyyrr, ppyyrr,
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B. Extending Mendelian Genetics 1. Incomplete
Dominance 2. Codominance 3. Multiple
alleles 4. Pleiotropy pleion (Greek for
more) a. one gene affecting many
phenotypes 5. Epistasis (Greek for standing
upon) a. a gene at one locus alters
phenotype of a gene at a second locus b.
Mice coat color and pigment deposit (color) or
not (albino) 6. Polygenic Inheritance a. an
additive effect of 2 or more genes on a single
phenotypic trait (converse to
pleiotropy) b. skin pigmentation (3
separately inherited genes)
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Comment

• Rh blood factor is a separate factor from the ABO
  blood group.
• Rh dominant
• Rh- recessive
• A blood dihybrid trait

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Skin Pigmentation Polygenic Inheritance Quantitati
ve character
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Summary for chapter 14

• Know the Mendelian crosses and their patterns.
• Be able to work simple genetic problems
  (practice).
• Watch genetic vocabulary.
• Be able to read pedigree charts.
• Understand carriers and be able to work
  problems with these.
• Know Huntington disease and sickle cell

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Chapter 15 Highlights

• Sex linked traits
• Duchenne Muscular dystrophy
• Hemophilia
• Color blindness
• Seen more in maleswhy?

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X inactivation in Females

• One of the X chromosomes is inactivated in each
  cell of a female during embryonic development.
• Inactive X is condensed and called a Barr
  bodylies along the inside of the nuclear
  envelope.
• Occurs randomly and independently (females
  consist of a mosaic of 2 types of cells)
• Example Tortoiseshell cat and Calico cats
• How is the X chromosome inactivated
• Modification of the DNA (attachment of a methyl
  group to nucleotides) chapter 18
• XIST gene

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Mapping the distance btw genes using
recombination data

• Recombination frequencies depend on the distance
  between genes on a chromosome
• Can create a linkage map from this data
• Distances btw genes are map units
• A map unit is 1 of recombination frequency
• Genes are linked if they are on the same
  chromosome

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How you tell if genes are linked
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A Test Cross to determine linkage and if linkage,
what is the percentage of recombination so you
can map the genes.
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They dont look like the parents
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Mutations of Chromosomes
1. Abnormal of Chromosomes
Nondisjunction a. members of a chromosome pair
fail to separate b. Meiosis I c. Meiosis II d.
Monosomic vs. Trisomic e. Abnormal of sex
chromosomes (aneuploidy) f.
polyploidy (triploidy 3n or tetraploidy 4n)
2. Alterations in chromosome structure a.
Deletion b. Duplication
c. Inversion d. Translocation
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Nondisjunction
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Alterations in Chromosomes

• Know the following disorders and causes for the
  disorders
• down syndrome
• Klinefelter syndrome
• Turner syndrome
• cri du chat

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Genomic Imprinting

• The differential expression of genetic material
  depending on whether it is inherited from the
  male or female parent
• Occurs during meiosis and results in the
  silencing of one allele of certain genes.
• Example mouse gene Igf2only the paternal gene
  is expressed (it had methyl groups attached to
  cytosine nucleotides) exception to the rule that
  methylated DNA is silenced (not expressed)
• Most imprinted genes are critical for embryonic
  development. (mouse experiment)normal
  development requires embryonic cells have exactly
  one copy of certain genes.

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Organelle genes

• Cytoplasmic genes genes outside of the nucleus
• Mitochondria, chloroplasts, other plant plastids
• Contain small circular piece of DNA
• Distributed to offspring from the maternal parent
  (egg)
• Mitochondrial diseases (Myopathy, Lebers
  hereditary optic neuropathy)