Units of Heredity

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Chapter 12

• Units of Heredity

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Sex Determination

• Thomas Hunt Morgan early 1900s
• Studied bred fruit flies
• Discovered the X and Y chromosomes
• Males XY Females XX
• Sex Linkage
• X-linked genes genes found on X
• Y-linked genes genes found on Y
• Studied eye color on fruit flies and found that
  eye color is carried on X chromosome

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Linkage Groups

• Linked 2 or more genes found on same chromosome
• Morgan studied body color and wing length
• Genes are on same chromosome

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Chromosome Mapping

• The farther apart genes are on a chromosome means
  that more likely to separated by crossing-over
• Chromosome map diagram that shows the linear
  sequence of genes on a chromosome
• Alfred Sturtevant used crossing over to
  construct a chromosome map of fruit flies
• Compared the frequency of crossing-over for
  several genes
• Genes separated by crossing-over 1 of the time
  are 1 map unit away from each other

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Mutations

• Mutations can involve an entire chromosome or a
  single DNA nucleotide
• Germ-cell mutations occurs in sex cells
• Somatic-cell mutations occurs in body cells
• Lethal mutations cause death

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Chromosome Mutations

• Deletion loss of a piece of DNA
• Inversion segment breaks off and then
  reattaches in reverse order
• Translocation segment breaks off and then
  attaches to another chromosome
• Nondisjunction failure of a chromosome to
  separate from its homologue during meiosis

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Gene Mutations

• Point mutations
• Substitution when 1 nucleotide in a codon is
  replaced with a different nucleotide
• Addition (insertion)
• Deletion
• Frame shift shifts codons down due to point
  mutation causing new amino acids (proteins)
• Sickle cell anemia defective form of hemoglobin
  which is found in RBCs and causes loss of RBCs
  and circulatory problems

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Pedigree

• Pedigree family record that shows how a trait
  is inherited over several generations
• Traits are inherited by studying phenotypes among
  members of the same species
• Patterns of inheritance phenotypes in repeated
  predictable pattern
• Carriers individuals who have one copy of an
  autosomal allele but do not express it

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Genetic Traits Disorders

• Traits controlled by a single allele
• Huntingtons Disease (HD)
• Cystic Fibrosis
• Sickle Cell Anemia
• Traits controlled by multiple alleles
• Blood type
• Polygenic traits controlled by 2 or more genes
• Skin color
• Eye color

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• X-linked traits
• Color blindness
• Hemophilia
• Duchenne muscular dystrophy
• Sex influenced traits
• Pattern baldness

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• Disorders due to nondisjunction
• Monosomy
• Trisomy
• Down syndrome
• Klinefelters syndrome
• Turners syndrome

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Y-linked Disorders

• Feather development in poultry
• Horn development in Dorset sheep
• Hairy ears in humans

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Diagnosing Trisomy 21
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Detecting Human Genetic Disorders

• Genetic screening examination of a persons
  genetic makeup
• Genetic counseling form of medical guidance
  that informs about problems that could affect
  offspring

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• Preventing fetal disorders
• Amniocentesis test to reveal fetal
  abnormalities
• Chronic villi sampling produces a karyotype
• Phenylketonuria (PKU) disorder in which the
  body cannot metabolize the amino acid phenylaline
• Can cause brain damage

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Much genetic information can be derived from
pedigrees (family genetic histories). Such
information is especially helpful in connection
with humans because
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• humans cannot be crossed experimentally
• other animals have long life spans
• we know relatively little about human genetics
• humans have so many chromosomes
• humans are too complicated

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Sickle-cell anemia patients have a different form
of _____, which leads to _____.
12.02

• hemoglobin, increased muscle activity
• a sex chromosome, sterility
• pigment, color blindness
• skin cell, nevi
• hemoglobin, decreased oxygen transport

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Individuals most protected against malaria are
those who
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• are heterozygous for sickle-cell anemia (one
  hemoglobin A, one hemoglobin S)
• are homozygous for sickle-cell anemia (two
  hemoglobin S)
• are hemophiliacs
• are homozygous for hemoglobin A
• both a and c

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Inheritance of a dominant autosomal disorder
differs from inheritance of an autosomal
recessive disorder in that
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• A dominant disorder may be passed on only if both
  parents are affected.
• A dominant disorder is evident only if the
  offspring is homozygous for the allele.
• A dominant disorder is more often seen in
  females.
• A dominant disorder may be passed on even if only
  one parent is affected.
• both b and d

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An individual having 44 autosomes and one X
chromosome would be classified as
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• polyploid
• aneuploid
• having Klinefelter syndrome
• having Turner syndrome
• both b and d

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A human embryo with 69 chromosomes would
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• die in the womb or shortly after birth
• be considered polyploid
• have fewer problems than a plant with the same
  condition
• both a and b
• all of the above

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Which of the following statements is not true
regarding Down syndrome?
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• Affected individuals usually have three copies of
  chromosome 21.
• The condition is usually caused by nondisjunction
  in egg formation.
• A woman over 35 increases her chance of having a
  Down syndrome child to 1 out of every 40 births.
• Approximately 0.1 percent of all live births are
  children with Down syndrome.
• The physical characteristics associated with the
  disorder include mental retardation, male
  infertility, short stature, and reduced life span.

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Nondisjunction can occur in
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• meiosis I or mitosis
• mitosis or meiosis II
• only meiosis II
• only meiosis I
• either meiosis I or II

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A carrier is a person who
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• suffers from a recessive disorder
• is heterozygous for a recessive disorder
• is homozygous for a recessive disorder
• does not suffer from a recessive disorder but
  possesses an allele for it
• b and d

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What do all human males inherit from their mother?
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• an X chromosome
• genes for red-green color vision
• two X chromosomes
• all of the above
• a and b only