Lecture Notes: Genetic Diagrams and Punnett Squares

Introduction

• Genetic diagrams or Punnett squares are tools to demonstrate monohybrid inheritance.
• Monohybrid inheritance involves characteristics controlled by a single gene.

Drawing a Punnett Square

1. Identify Parent's Genome
   • Use any letter for the gene; dominant genes are capital letters, recessive genes are lowercase.
2. Create the Table
   • Split the alleles from each parent.
   • Each parent's alleles are placed into boxes representing gametes.
3. Filling the Punnett Square
   • Combine alleles from each parent to predict offspring.
   • Dominant alleles are listed first.

Example: Cystic Fibrosis

• Cystic Fibrosis is an inherited disorder caused by a recessive allele.
• Problem: Determine the probability that a child will have cystic fibrosis.
  • Recessive allele: lowercase 'f'.
  • Punnett Square Layout:
    • Box 1: FF
    • Box 2: FF
    • Box 3: Ff
    • Box 4: Ff
  • Result: 0% chance for a child to have cystic fibrosis in this example.

Using Family Pedigrees

• Pedigrees help trace genetic disorders in families.
• Example with Sue's Family:
  • Sue's mother (Steph) has cystic fibrosis (ff).
  • Sue's father (Larry) is a carrier (Ff), as Sue’s sister Paula has the disease.
  • Punnett Square Analysis:
    • Shows a 50% chance of offspring having cystic fibrosis.

Gender Probability Prediction

• Gender determination can also be predicted using genetic diagrams.
  • Male: XY chromosomes
  • Female: XX chromosomes
• Probability: 50% chance of being born male or female when considering the sex chromosomes.

Additional Information

• Instructor: Mr. Science (Saleem)
• Reminder to like, subscribe, and visit www.mrscience.com for more resources.

These notes cover the key concepts and examples discussed in the lecture on genetic diagrams and Punnett squares, offering insights into how to predict genetic outcomes for certain traits and conditions.