Genetic Disorders

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Genetic Disorders
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Review

• Parents pass traits to their offspring through
  their genes.
• Genes are located on bigger structures called
  chromosomes each person has 46 of these, which
  are joined into 23 pairs.
• Each parent contributes one-half of each pair.
• It's how those genes work together that makes you
  unique!

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Diseases

• Scientists have discovered that some medical
  disorders are genetic.
• Problems arise when the disease gene is dominant
  or when the same recessive disease gene is
  present on both chromosomes in a pair. 

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• If a person carries the dominant gene for a
  disease, he or she will usually have the disease
• Diseases caused by a dominant gene include
• Marfan syndrome (a connective tissue disorder).
  People with Marfan have an increased risk that
  their aorta will enlarge and eventually rupture.
• Huntington disease (a degenerative disease of
  the nervous system).

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Carriers

• People who have one recessive gene for a disease
  are called carriers, and they don't usually have
  the disease because they have one normal,
  dominant gene. In other words, their genotype
  for this trait is heterozygous.
• However, when two carriers have a child together
  the child has a 1 in 4 (25) chance of getting
  the disease gene from both parents, which results
  in the child having the disease.

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Examples of Recessive Disorders

• Disorders that occur when recessive disease genes
  from both parents come together in a child.
  (homozygous recessive)
• Cystic fibrosis (a lung disease)
• Sickle cell anemia (a blood disease)
• Tay-Sachs disease (which causes nervous system
  problems)

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If both parents are carriers (heterozygous) what
is the probability that they will pass this
recessive gene to their child? Complete a
Punnett Square to model the probabilities. N
normal red blood cell n sickle cell.
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X-linked Genetic Disorders

• You have 23 pairs of genes and one of the pairs
  determines what gender you are male or female
• Boys XY Girls XX
• Some recessive genes are carried only on the X
  chromosome, which means that usually only males
  can develop the disease because they have only
  one X chromosome.
• Females have two X chromosomes, so they would
  need to inherit two copies of the recessive gene
  to get the disease.

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X-linked disorders

• X-linked disorders include color blindness and
  the bleeding disorder hemophilia.
• Hemophilia is a genetic disorder in which a
  person's blood does not clot properly.
• A person who has hemophilia has a tendency to
  bleed excessively. 
• The Royal Courts of Europe provide an interesting
  case study of hemophilia in a family tree.

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The Royal Disease

• Normally, hemophilia is quite rare.
• But because royal families usually married people
  from other royal families, there was more of a
  chance that children would inherit the gene for
  this trait.
• Queen Victoria of England (1837-1901) was a
  carrier of the hemophilia gene and subsequently
  passed the disease on to several royal families.

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• Two of Queen Victoria's daughters, Alice and
  Beatrice, were carriers of hemophilia.
• They passed the disease on to the Spanish, German
  and Russian royal families, ensuring that the
  disease would be present in future generations.

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Genetic Mutation

• Some genetic disorders are caused by mutations in
  genes.
• Brainpop! Genetic Mutation