Chapter 4

Heredity and Evolution

Epigenetics• http://video.pbs.org/video/15251074

73/• LA Times Article

Gregor MendelA monk living in

what is now the Czech Republic

Living in an abbey he crossed different strains of purebred plants and studied their progeny.

His work illustrates the basic rules of inheritance.

Traits Mendel Studied in Peas

Dominance• Dominant traits are governed by an

allele that can be expressed in the presence of another, different allele. – Dominant alleles prevent the expression

of recessive alleles in heterozygotes.

Recessiveness• Recessive traits are not expressed in

heterozygotes.– For a recessive allele to be expressed,

there must be two copies of the allele.