The Human Genome

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The Human Genome

• Biology
• Chapter 14

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14-1 Human Heredity
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Human Chromosomes

• Karyotype a picture of chromosomes arranged in
  pairs

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Human Chromosomes

• 2 types of chromosomes
• Sex chromosomes X and Y
• Because they determine the sex of the individual
• Sex determination
• XX female
• XY male
• Autosomes 1-22
• All human egg cells carry a single X chromosome
  but ½ of all human sperm have a X and the other ½
  contain a Y

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Making a Pedigree

• Pedigree
• A graphic representation of genetic inheritance
• Shows the relationships within a family
• Made up of a set of symbols that identify
• males and females
• Individuals affected by that trait being studied
• Family relationships
• squares male circles female

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Making a Pedigree

• Pedigree (cont.)
• Shaded circles and squares individuals showing
  the trait
• Un-shaded circles and squares individuals not
  showing the trait
• Half shaded circles and squares individuals who
  are heterozygous (carrier) for the trait
• Carrier - is someone who is heterozygous for a
  trait

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Analyzing a Pedigree
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Multiple Alleles in Humans

• Blood type
• In humans, there are four blood types
  (phenotypes) A, B, AB, and O
• Blood type is controlled by three alleles.
• A, B, O
• O is recessive
• A and B are codominant.
• Crosses involving blood type often use an I to
  denote the alleles - see chart.

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Simple Recessive Heredity

• Most genetic disorders are caused by recessive
  alleles
• Cystic fibrosis
• Common among white Americans
• 120 whites carry the recessive allele
• Affects the lungs and digestive tract

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Simple Recessive Heredity

• Tay-Sachs disease
• Common among Jews in the US
• Affects central nervous system
• Phenylketonuria (PKU)
• Affects people whose ancestors came from Norway
  or Sweden
• Inability to break down phenylalanine

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Simple Dominant Heredity

• Tongue rolling
• Freely hanging earlobes
• Hitchhikers thumb
• Thick lips
• Huntingtons disease
• Lethal genetic disorder
• Breakdown in areas of the brain
• Onset between 30-50 years old

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Codominance in Humans

• Sickle-cell anemia
• Affects
• black Americans with African decent
• white Americans who are descendants of families
  in the Mediterranean Sea
• Homozygous for the allele produce the abnormal
  RBCs
• Heterozygous for the allele produce both normal
  and abnormal RBCs

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14-2 Human Chromosomes
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Complex Patterns of Inheritance

• Sex-linked inheritance
• Traits that are only located on sex chromosomes
• i.e. they will be on X or Y but not both
• Most all known sex-linked disorders are on the X
  chromosomes
• Red-green color blindness
• Males have just one X chromosomes. Thus, all
  X-linked alleles are experssed n males, even if
  they are recessive
• X linked
• Hemophilia
• X linked
• Queen Victorias family

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Chromosomal Disorders

• Nondisjunction failure of homologous
  chromosomes to separate during meiosis resulting
  in an abnormal number of chromosomes in the
  fertilized egg
• Down Syndrome Trisomy 21
• Occurs when the a zygote receives one 21
  chromosome from one parent and two from the other
  parent

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Chromosomal Disorders

• Nondisjunction Sex Chromosome Disorders
• Turner Syndrome
• Occurs when the zygote receives one X chromosome
  from one parent and none from the other parent
• Klinefelters Syndrome
• Occurs when the zygote recieves two X and one Y
  resulting in three sex chromosome (XXY)

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14-3 Human Molecular Genetics
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Mapping and Sequencing the Human Genome

• Human Genome
• Map of the (80,000) genes on 46 human
  chromosomes that when mapped and sequenced, may
  provide information on the treatment or cure of
  genetic disorders
• Linkage map
• The genetic map that shows the location of genes
  on a chromosome

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Human DNA Analysis

• Diagnosis of genetic disorders
• If the location of a specific gene is known then
  the child could be diagnosed before birth
• Gene therapy
• The insertion of normal genes into humans cells
  to correct genetic disorders
• DNA fingerprinting
• Can be used by law-enforcement to determine a
  persons presence at a crime scene