 He discovered different laws and rules that explain factors affecting heredity.

 The two alleles for a trait must separate when gametes are formed  A parent randomly passes only one allele for each trait to each offspring

 The genes for different traits are inherited independently of each other.

 Each organism has two alleles for each trait Alleles - different forms of the same gene Genes - located on chromosomes, they control how an organism develops Need to Know!

 The trait that is observed in the offspring is the dominant trait (uppercase- DD)  The trait that disappears in the offspring is the recessive trait (lowercase dd)

 Phenotype - the way an organism looks red hair or brown hair  Genotype - the gene combination of an organism AA or Aa or aa Need to Know!

 Heterozygous - if the two alleles for a trait are different (Aa)  Homozygous - if the two alleles for a trait are the same (AA or aa) Need to Know!

 A Punnett square is a chart which shows/predicts all possible gene combinations in a cross of parents (whose genes are known).  Punnett squares are named for an English geneticist, Reginald Punnett. He discovered some basic principles of genetics, including sex linkage and sex determination. Need to Know!

 Setting up and using a Punnett square is quite simple once you understand how it works. You begin by drawing a grid of perpendicular lines:

 Next, you put the genotype of one parent across the top and that of the other parent down the left side. For example, if parent pea plant genotypes were YY and GG respectively, the setup would be: Note that only one letter goes in each box for the parents. It does not matter which parent is on the side or the top of the Punnett square.

 Next, all you have to do is fill in the boxes by copying the row and column-head letters across or down into the empty squares. This gives us the predicted frequency of all of the potential genotypes among the offspring each time reproduction occurs.

 What is the phenotype?  What is the genotype?  What is homozygous?  What is heterozygous?  What do we call the trait that is observed?  What case (upper or lower) is it written in?  What about the one that disappears?  What case is it written in?

1. In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a cross of two plants that are heterozygous for the seed shape trait, what percentage of the offspring should have spherical seeds? Need to Know!

75%