Introduction

Gregor Mendel is considered to be the ‘Father’ of modern genetics.  It is important to realize that Mendel performed his research long before science had discovered DNA, chromosomes, or the process of Meiosis.  How did Mendel make his discoveries without the benefit of this knowledge? Let us review his experiments to understand how he arrived at his conclusions.

The following video explains how to set up a Punnett Square.

Summary

• In this section, we have learned the following:
• Inherited traits in the pea plants seemed to be controlled by a pair of ‘factors’, which are now called genes or alleles.
• Genes come in different versions called alleles. A dominant allele hides a recessive allele and determines the organism’s appearance.
• The genotype of a plant represents the combination of alleles/genes present (i.e. ‘Pp’)
• The phenotype of the plant is the physical/observable result from the plant’s genotype.
• A plant that is homozygous for a gene has two identical copies of the same allele present.
• A plant that is heterozygous for a gene has two different copies of the alleles for that particular trait. 
• When Mendel cross-pollinated two true-breeding plants that are different in one trait, he found that the resulting plants resembled only one of the parent plants. The trait found in this F1 generation is considered dominant.
• Mendel proposed that pairs of factors in a parental generation seemed to segregate into different gametes that when combined together form a new genotype for the offspring.  This is the basis of Mendel’s Law of Segregation
• Mendel also proposed that if you examined two traits in a pea plant, the alleles for the two traits are separated into gametes completely independently of each other during the process of Meiosis.  This principle provides the basis for Mendel’s Law of Independent Assortment.
• A Punnett square can be used to predict genotypes (allele combinations) and phenotypes (observable traits) of offspring from genetic crosses.

Sources:

“Learn Biology: How to Draw a Punnett Square.” Uploaded by MahaloBiology, Jan 14, 2011, Retrieved from https://youtu.be/Fr6pEgNnjdQ