Genes and Medical Genetics

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Genes and Medical Genetics
Genotype and Phenotype Dominant and
Recessive Inheritance Patterns Sex-Linked Traits
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Genotype and Phenotype

• Genotype genetic makeup--genes
• Phenotype physical makeup--looks,
  characteristics
• Genes code for proteins
• Genes linked to Characteristics physical,
  behavioral, intellectual and many other traits
• Trait--characteristic
• Allele

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Allele

• Allele Alternate form of a gene at same
  position on pair of chromosomes that affect the
  same trait.
• Dominant Allele Capital Letter--O
• Recessive Allele lowercase letter--o
• Homozygous Dominant--OO
• Homozygous Recessive--oo
• Heterozygous--Oo

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Phenotype and Genotype

• Phenotype is determined by Genotype
• Punnet Square
• Determine Phenotype
• Predict Ratios among Offspring
• Figure odds of genetically determined
  characteristics

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Autosomal Recessive Disorders

• Tay-Sachs Disease
• Jewish people in USA (E. Euro descent)
• Not apparent at birth
• 4 to 8 months
• Neurological impairment evident
• Gradually becomes blind and helpless
• Develops uncontrollable seizures/paralyzed
• Allele is on Chromosome 15
• Lack of enzyme hexosaminidase A (Hex A)
• Lysosomes dont work, build up in brain

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Autosomal Recessive Disorders

• Cystic Fibrosis
• Most common in USA (Caucasian)
• 1 in 20 caucasians is a carrier
• Mucus in bronchial and pancreas thick/viscous
• Breathing and food digestion problems
• Allele is on chromosome 7
• Cl ions can not pass through plasma membrane
  channels
• Cl ions pass water goes with it. No water,
  thick mucus

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Autosomal Recessive Disorders

• Phenylketonuria (PKU)
• Affects in in 5,000 newborns
• Most common nervous system disorder
• Allele is on chromosome 12
• Lack the enzyme needed for the metabolism of the
  amino acid phenylalanine
• A build up of abnormal breakdown pathway
• Phenylketone
• Accumulates in urine. If diet is not checked,
  can lead to severe mental retardation

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Autosomal Dominant Disorders

• Neurofibromatosis
• Very common genetic disorder
• Tan spots on skin
• Later tumors develop
• some sufferers have large head and ear and eye
  tumors.
• Allele is on chromosome 17
• Gene controls the production of a protein called
  neurofibromin
• This naturally stops cell growth

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Autosomal Dominant Disorders

• Huntington Disease
• Leads to degeneration of brain cells
• Severe muscle spasms and personality disorders
• Attacks in middle age
• Allele is on chromosome 4
• Gene controls the production of a protein called
  huntington
• Too much AA glutamine. Changes size and shape of
  neurons

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Incomplete Dominant traits

• Sickle Cell Anemia
• Controlled by intermediate phenotypes at a ratio
  of 121
• Red blood cells are not concave
• Normal Hemoglobin (HbA). Sickle cell (HbS)
• HbA-HbA-normal Hbs-Hbs sickle cell
• HbA-Hbs- have the trait

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Sickle Cell Anemia
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Pedigree Charts

• Pedigree charts can help determine if disorders
  are dominant or recessive.
• Malessquares, Femalescircles.
• Carrier appear healthy but have one allele, one
  copy of mutated gene.
• Pattern I Autosomal recessive--both parents are
  carriers, child affected.
• Pattern II Autosomal dominant--one parent is
  affected, affected child can have healthy sibling.

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Sex-Linked Traits

• Characteristics from genes on sex chromosomes.
• Genes on Sex chromosomes encode sex-linked
  traits.
• Allele on X chromosomeX-linked trait
• Allele on Y chromosomeY-linked trait
• Ysmall, very few traits
• Xlarge, several traits

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X-Linked Traits

• Color Blindness
• Muscular Dystrophy
• Hemophilia

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Sex-Influenced Traits

• Traits such as baldness and finger length are sex
  influenced.
• Trait is determined by an autosomal gene, but
  these genes respond differently to hormones.
• For example, baldness is enhanced by
  testosterone.
• Baldness is also dominant in males and recessive
  in females.

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Genetic Profiling

• We have the technology.
• We could screen everyones DNA for mutations.
• How would this affect insurance?
• How would this affect health care?
• What about reproductive control?
• What do you think?