Mendel’s Theory

Section 2

Explaining Mendel’s Results

• Mendelian theory of heredity explains simple patterns of inheritance. In these patterns, two of several versions of a gene combine and result in one of several possible traits.

Alternate versions of genes

• Allele- a version of a gene

Dominant and recessive alleles

• Dominant- An allele that is fully expressed whenever the allele is present in an individual.

• Recessive- An allele that is expressed only when no dominant allele is present for an individual.

Random segregation of Alleles

• In modern terms, the law of segregation holds that when an organism produces gametes, each pair of alleles is separated and each gamete has an equal chance of receiving either one of the alleles.

Genotype and Phenotype

• Genotype- the set of alleles that an individual has for a character

• Phenotype- the trait that results from a set of alleles

• Genotype results from phenotype

Homozygous and Heterozygous

• Homozygous- Describes an individual that has identical alleles for a trait on both homologous chromosomes.

• Heterozygous-Describes an individual that carries two different alleles of a gene.

Mendel’s second experiments

• Dihybrid cross- involves to characters, such as seed color and seed shape

Independent Assortment

• In modern terms, the law of independent assortment holds that during gamete formation, the alleles of each gene segregate independently.