Examples of genetic crosses

• Genetic inheritance controls the characteristics of all living things
• Our genes are inherited from our parents, and the different combinations of these genes make us unique
• Examples of genetic crosses:

  • Aa x AA where Aa = female alleles and AA = male alleles
  • Ee x Ee where Ee = female alleles and Ee = male alleles
• Half of the possible offspring have the same allele combination; AA homozygous dominant and the other half have the Aa heterozygous combination
• Probability calculations for Aa x AA:

  • Two out of four possible combinations create 50% chance for AA, and 50% chance for Aa alleles
  • Ratio of 1:1
• Probability calculations for Ee x Ee:

  • One out of four possible combinations create 25% chance for EE, two offspring create a 50% chance for the Ee alleles, and finally 25% chance for the ee alleles
  • Ratio of 1:2:1
• Coat type in dogs is determined by a single gene with two alleles:

  • Straight coat allele (D) is dominant
  • Curly coat allele (d) is recessive
• Punnett square for Dd x Dd:

  • D d
  • D DD Dd
  • d Dd dd
  • Ratio of 3 straight : 1 curly
• Probability of offspring having the combination DD is 25%
• Estimate for how many offspring will have pink flowers when a homozygous recessive plant is bred with a heterozygous plant:

  • Offspring that are Aa are pink so there is a 50% probability of a plant being pink
  • Calculation: 48 × (50 ÷ 100) = 24 plants