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Units of Heredity

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Approximately 0.1 percent of all live births are children with Down syndrome. ... statements is not true regarding Down syndrome? meiosis I or mitosis ... – PowerPoint PPT presentation

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Title: Units of Heredity


1
Chapter 12
  • Units of Heredity

2
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

7
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

8
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

9
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

13
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

22
Y-linked Disorders
  • Feather development in poultry
  • Horn development in Dorset sheep
  • Hairy ears in humans

23
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

30
Much genetic information can be derived from
pedigrees (family genetic histories). Such
information is especially helpful in connection
with humans because
12.01
  • 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

31
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

32
Individuals most protected against malaria are
those who
12.03
  • 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

33
Inheritance of a dominant autosomal disorder
differs from inheritance of an autosomal
recessive disorder in that
12.04
  • 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

34
An individual having 44 autosomes and one X
chromosome would be classified as
12.05
  • polyploid
  • aneuploid
  • having Klinefelter syndrome
  • having Turner syndrome
  • both b and d

35
A human embryo with 69 chromosomes would
12.06
  • 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

36
Which of the following statements is not true
regarding Down syndrome?
12.07
  • 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.

37
Nondisjunction can occur in
12.08
  • meiosis I or mitosis
  • mitosis or meiosis II
  • only meiosis II
  • only meiosis I
  • either meiosis I or II

38
A carrier is a person who
12.09
  • 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

39
What do all human males inherit from their mother?
12.10
  • an X chromosome
  • genes for red-green color vision
  • two X chromosomes
  • all of the above
  • a and b only
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