Edexcel A (SNAB) A Level Biology:复习笔记2.4.5 Monohybrid Crosses

• Monohybrid inheritance looks at how the alleles for a single gene are passed on from one generation to the next
• Known information about the genotypes, phenotypes and the process of meiosis are used to make predictions about the phenotypes of offspring that would result from specific breeding pairs
• When two individuals sexually reproduce there is an equal chance of either allele from their homologous pair making it into their gametes and subsequently the nucleus of the zygote
  • This means there is an equal chance of the zygote inheriting either allele from their parent
• Genetic diagrams are often used to present this information in a clear and precise manner so that predictions can be made
  • These diagrams include a characteristic table called a Punnett square
• The predicted genotypes that genetic diagrams produce are all based on chance
  • There is no way to predict which gametes will fuse so sometimes the observed or real-life results can differ from the predictions

Genetic crosses can be shown by a Punnet square

Monohybrid Punnett square with Heterozygotes Table

• Predicted ratio of phenotypes in offspring – 3 black coat : 1 chestnut coat
• Predicted ratio of genotypes in offspring – 1 BB : 2 Bb : 1 bb