4.6 : Mendel's Law of Segregation

Mendel’s Law of Segregation

Gregor Mendel, through his pioneering experiments with pea plants, formulated the Law of Segregation. This law states that during the formation of gametes (sperm and egg cells), the two alleles for a trait separate, so each gamete carries only one allele for each gene. This law explains how offspring inherit one genetic allele from each parent, maintaining genetic variation and allowing for predictable patterns of inheritance.

Science and Engineering Practices (SEP): Analyzing and Interpreting Data

Understanding genetic inheritance requires analyzing patterns and interpreting data to predict how traits are passed from one generation to the next. By examining inheritance through Punnett squares, simulations, and real-world examples, scientists and students can explore how dominant and recessive traits are distributed in populations.

Activity Ideas:

• Predict Genetic Outcomes: Use Punnett squares to determine the probability of dominant and recessive traits appearing in offspring.
• Examine Family Traits: Analyze inherited traits in your own family, such as eye color, hair type, or dimples, to observe how segregation contributes to genetic variation. Compare patterns across generations to identify dominant and recessive traits.
• Genotypic and Phenotypic Ratios: Conduct a simulated cross for traits such as pea plant height or flower color. Calculate and compare the expected vs. observed ratios in that simulated cross.

By analyzing genetic data, you can better understand how traits are inherited and why individuals within a family can look different from one another.

Crosscutting Concept (CCC): Cause and Effect

Mendel’s Law of Segregation demonstrates clear cause-and-effect relationships in genetics. When alleles separate during meiosis, they directly influence the traits seen in offspring.

• Cause: Parents contribute one allele each to offspring.
  Effect: Each offspring inherits a unique combination of genetic traits.
• Cause: Recessive alleles are masked when paired with dominant alleles.
  Effect: Some traits only appear if both inherited alleles are recessive.
• Cause: Random segregation of alleles during gamete formation.
  Effect: Genetic variation occurs, allowing for diversity within populations.

For example, if both parents have brown eyes but carry a recessive allele for blue eyes, their child may inherit two recessive alleles and have blue eyes. Understanding these patterns helps scientists predict inherited traits and study genetic disorders.