Genetics: Punnett Squares and Independent Assortment (hard difficulty)

Punnett Squares

• Punnett squares are used to show the possible genotypes of offspring by combining the alleles of gametes.

Mendel's Second Law of Independent Assortment

• Two genes on different chromosomes segregate their alleles independently.
• The inheritance of an allele of one gene does not influence which allele is inherited at a second gene.
• In a dihybrid cross, the alleles of each gene assort independently.
• The segregation of different allele pairs is independent.
• Independent alignment of different homologous chromosome pairs during metaphase I leads to the independent segregation of different allele pairs.

Independent Assortment of Two Traits

• In a dihybrid cross, parents with two differing traits are crossed.
• The alleles of each gene are independent, and the segregation of different allele pairs is independent.
• The F2 generation shows all four possible phenotypes in a set ratio of 9:3:3:1.
• The ratio of phenotypes can be explained by the independent assortment of two traits.

Modern Genetics

• A defective copy of a gene is a mutation.
• Pedigree analysis is used to determine the inheritance pattern of a trait.
• Symbols are used in pedigree analysis to represent different individuals and their relationships.

Interpreting the Data

• The F1 generation showed only one of the two parental traits.
• The F2 generation showed an approximately 3:1 ratio of the two parental traits.
• The results refuted a blending mechanism of heredity and suggested a particulate theory of inheritance.
• Mendel postulated that a pea plant contains two discrete hereditary factors for a given character, one from each parent.

Mendel's Experiments

• Mendel studied seven characters that bred true.
• The morphological characteristics of an organism are termed characters.
• A variety that produces the same trait over several generations is termed a true-breeder.
• Mendel did not have a hypothesis to explain the formation of hybrids, but rather believed that a quantitative analysis of crosses may provide mathematical relationships that govern hereditary traits.
• Mendel's experiments involved crossing two variants of the same characteristic, and he also performed dihybrid crosses, crossing individual plants that differ in two characters.

Learn about Punnett squares and Mendel's Second Law of Independent Assortment, understanding how alleles combine and segregate independently in genetics.