Genetic inheritance

• Human body cells


  22 control each pair, have 23 pairs or chromosomes
• Characteristics and the chromosomes

  • Look very similar
  • The 23rd pair carries sex determining genes and the other chromosomes can look different to each other
  • X chromosomes are much larger than Y chromosomes
• The two possible chromosomes in the 23rd pair


  X and Y chromosomes
• When gamete cells undergo meiosis to form, one sex Chromosome goes into each gamete
• Females


  Have two X chromosomes in their eggs
• Males


  Have one X and one Y chromosomes in their sperm
• Punnett Squares


  Can be used to show sex inheritance
• There is a 50% chance of the child being female and a 50% chance of the child being male
• Genes are passed on from the parent in sex cells
• Identical twins have the same genotype
• Gene


  A section of DNA that codes for a particular protein
• Allele


  Different forms of the same gene
• Dominant allele


  Only one copy is needed to be expressed
• Recessive allele


  Two copies are needed to be expressed
• Genotype


  Combination of alleles an individual has
• Phenotype


  Physical characteristics that are observed
• Inherited disorders


  • Polydactyly (extra fingers/toes)
  • Cystic fibrosis
• Polydactyly is caused by a dominant allele
• Cystic fibrosis is caused by a recessive allele, requiring both parents to be carriers or one to have it and the other to be a carrier