Human Heredity Sections 14-1 and 14-2

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Human HereditySections 14-1 and 14-2

• Objectives
• 7.2 Interpreting inheritance patterns shown in
  graphs and charts
• 8.5 Relating genetic disorders and disease to
  patterns of genetic inheritanceExamples
  hemophilia, sickle cell anemia, Down's syndrome,
  Tay-Sachs disease, cystic fibrosis, color
  blindness, phenylketonuria (PKU)

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Human Chromosomes

• How many chromosomes do we have?
• Answer 46
• How many of those are sex chromosomes?
• Answer 2
• What are the possible combinations of sex
  chromosomes?
• Answer XX or XY
• What are the other chromosomes called?
• Answer autosomes

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Karyotype
Source http//www.dnalc.org/view/16243-Gallery-8-
Human-female-karyotype.html

• Def a picture of chromosomes, taken in mitosis
  metaphase, and paired up.
• Why would the picture be taken at this point?

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Pedigree Charts
Source http//www.citruscollege.edu/lc/archive/bi
ology/Pages/Chapter10-Rabitoy.aspx
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Pedigree Charts Activities

• Class Activity Figure 14-3, p.342
• Individual Assignment Problem Solving, p.343.
  Add the following questions
• Identify the genotype of each individual.
• Is albinism a dominant or recessive trait?
• What is the probability of the second-generation
  couple having another albino child?

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Sex-Linked Genes

• The X chromosome is much larger than the Y
  chromosome, carrying many more genes. (See Figure
  14-12, p.350)
• More than 100 sex-linked genetic disorders have
  been mapped to the X chromosome.

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Sex-Linked Genes

• Since males have only one X chromosome, if an
  allele for a disorder is present on that
  chromosome, the trait will be expressed.
• Common sex-linked disorders
• Colorblindness
• Color vision is controlled by three genes on the
  X chromosome.
• 1 in 10 males in the U.S. have some form of
  colorblindness.
• Hemophilia 2 genes on the X chromosome help
  control blood clotting (1/10,0000)
• Duchenne Muscular Dystrophy (1/3000)

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X-Chromosome Inactivation

• Females have two X chromosomes.
• One of those chromosomes is switched off,
  becoming a Barr body --- a dense (but inactive)
  region in the nucleus.
• Males cannot switch off their X chromosome.

Source http//www.123rf.com/photo_2531003_spotted
-cat-with-no-tail-stands-attentive-and-alert.html
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Chromosomal Disorders

• Nondisjunction of homologous chromosomes during
  _____________, would give gametes abnormal
  numbers of chromosomes.
• When these gametes become diploid again, the
  number of chromosomes is abnormal.
• Some of these zygotes cannot survive others
  produce offspring with genetic disorders.

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Chromosomal Nondisjunction
Source http//drugline.org/img/term/meiotic-nondi
sjunction-9351_3.JPG
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Some Nondisjunction Disorders

• Down syndrome
• Autosomal nondisjunction
• 3 copies of chromosome 21 (trisomy 21)

Source http//www.buzzle.com/articles/teaching-ch
ildren-with-down-syndrome.html
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Some Nondisjunction Disorders

• Sex chromosome disorders
• Turners syndrome females with only one X
  chromosome
• Fertile
• Sex organs do not develop at puberty
• Klinefelters syndrome males with too many X
  chromosomes
• Interferes with meiosis, usually not permitting
  reproduction
• No known cases of babies born without an X
  chromosome, so it must contain genes important
  for survival.

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Some Nondisjunction Disorders

• Sex chromosome disorders
• Y chromosome contains a sex-determining region
  necessary to produce male sexual development
• Can develop even in the presence of multiple X
  chromosomes
• Will not develop if this region of the Y
  chromosome is absent.

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DISORDER DETECTIVES ACTIVITY

• http//www.youtube.com/watch?vth6Njr-qkq0