Why We Inherit Diseases

• What are inherited disorders?

  Conditions passed on through certain alleles
• What is polydactyly?

  Condition with extra fingers or toes
• How is polydactyly inherited?

  It is caused by a dominant allele
• What happens if one allele is for polydactyly?

  The disorder will still be present
• What is the genotype of a heterozygous individual with polydactyly?

  One dominant and one normal allele
• What is the outcome of crossing a heterozygous individual with a homozygous normal individual for polydactyly?

  • Possible offspring:
  • 2 heterozygous (polydactyly)
  • 2 homozygous normal
  • Phenotype ratio: 1:1
  • 50% chance of polydactyly
• How is cystic fibrosis inherited?

  It is caused by a recessive allele
• What does cystic fibrosis affect?

  Cell membranes, causing thick mucus
• What is the genotype needed to have cystic fibrosis?

  Two recessive alleles
• What is the frequency of carriers for cystic fibrosis in the population?

  1 in 25 people
• What are the results of crossing two carriers for cystic fibrosis?

  • Parent phenotypes: both normal
  • Parent genotypes: both heterozygous
  • Offspring outcomes:
  • 1 homozygous dominant
  • 2 heterozygous (carriers)
  • 1 homozygous recessive (cystic fibrosis)
  • Phenotype ratio: 3 normal : 1 cystic fibrosis
• What is embryo screening?

  Testing embryos for genetic disorders
• What happens if a genetic disorder is found during embryo screening?

  Parents may discard that embryo
• What are the advantages and concerns of embryo screening?

  Advantages:

  • Reduces suffering from genetic disorders
  • Saves money on treatments

  
  

  Concerns:

  • Implies genetic problems are undesirable
  • Potential for screening non-health traits
• What is a potential future concern regarding embryo screening?

  Screening for traits like eye color
• What are inherited disorders?

  Conditions passed on through certain alleles
• What are the two examples of inherited disorders discussed?

  Polydactyly and cystic fibrosis
• What laws exist in the UK regarding embryo screening?

  Many laws prevent unethical screening
• What is polydactyly?

  Condition with extra fingers or toes
• What type of allele causes polydactyly?

  It is caused by a dominant allele
• If one allele is polydactyly, what is the outcome?

  The disorder will still be present
• What happens when a heterozygous individual with polydactyly is crossed with a homozygous normal individual?

  Produces two heterozygous and two homozygous normal offspring
• What is the probability of having an offspring with polydactyly in this scenario?

  50% chance of having polydactyly
• What type of allele causes cystic fibrosis?

  It is caused by a recessive allele
• What is cystic fibrosis a disorder of?

  It is a disorder of cell membranes
• What does cystic fibrosis result in?

  Thick sticky mucus in the body
• What allele represents cystic fibrosis?

  Lowercase f represents the recessive allele
• How many recessive alleles are needed to have cystic fibrosis?

  Two recessive alleles are needed
• What do we call individuals with one copy of the cystic fibrosis allele?

  They are called carriers
• What is the outcome when two carriers of cystic fibrosis are crossed?

  Produces one homozygous dominant, two heterozygous, and one homozygous recessive
• What is the phenotype ratio of offspring from two cystic fibrosis carriers?

  Three normal phenotypes to one cystic fibrosis
• What is embryo screening?

  Checking embryo genes for genetic disorders
• What happens if a genetic disorder is found during embryo screening?

  Parents may discard that embryo
• What are the advantages of embryonic screening?

  • Reduces overall suffering from health problems
  • Saves money on treating genetic disorders
• What are the concerns regarding embryonic screening?

  • Implies genetic problems are less desirable
  • Potential for screening other traits in the future
• What is the current legal status of screening for traits like eye color in the UK?

  There are laws preventing such practices