Mendel’s Laws

What we already know…

• “Inheritable factors” or genes are responsible for all heritable characteristics

• Phenotype is based on Genotype

• Each trait is based on two genes, one from the mother and the other from the father

• True-breeding individuals are homozygous (both alleles are the same)

Mendel’s Laws: Unit Factors

• The appearance of each plant was determined by two “inheritance factors”

• Each organism has two alleles for each trait

Mendel’s Laws: Rule of Dominance

• “Inheritance factors” can be either dominant or recessive

• Observed traits are dominant, traits that disappear are recessive

– Homozygous Dominant (TT): two dominant alleles, shows dominant trait

– Homozygous Recessive (tt): two recessive alleles, shows recessive trait

– Heterozygous (Tt): has one dominant allele and one recessive allele, shows dominant trait

Mendel’s Laws: Law of Segregation

• “Inheritance factors” separate randomly when sex cells are formed

• This means each parent can only pass on ONE copy of their two genes to each offspring

• This is RANDOM, like the flip of a coin

Mendel’s Laws: Law of Independent Assortment

• “Inheritance factors” for different traits are passed from parents to their offspring independently of one another

• Genes for different traits are inherited independently of each other…– Genes for different traits are often on

different chromosomes, which separate according to the law of segregation when gametes are formed