Genetic Inheritance

• A gamete is a sex cell
• Chromosomes are long threads of DNA contained inside the cell's nucleus
• Alleles are different versions of the same gene
• A dominant allele is always expressed even if one copy is present
• A recessive allele is only expressed if two copies are present (therefore no dominant allele present)
• Homozygous alleles are both identical for the same characteristic, e.g. AA or aa
• Heterozygous alleles are both different for the same characteristic, e.g. Aa
• Most characteristics are a result of multiple genes interacting, rather than a single gene
• The alleles present, or genotype, operate at a molecular level to develop characteristics that can be expressed as a phenotype
• Polydactyly (having extra fingers or toes) is caused by a dominant allele
• Cystic fibrosis (a disorder of cell membranes) is caused by a recessive allele
• Embryos can be screened for genetic disorders
• Arguments for embryonic screening

  • Stop people from suffering
  • Less money spent by government on treating genetic disorders
  • There are laws to stop it from going to far
• Arguments against embryonic screening

  • Could cause prejudice
  • Designer babies
  • Screening is very expensive
• In females the sex chromosomes are the same (XX)
• In males the chromosomes are different (XY)