Basic Principles of Mendelian Genetics

Mendelian genetics is a way to understand how traits pass from parents to their offspring. This idea was started by a scientist named Gregor Mendel in the 1800s. There are two main ideas, or laws, that help explain this process:

1. Law of Segregation:

   • This law says that each person has two versions of a gene, one from each parent.
   • When parents produce eggs or sperm, these gene versions split up so that each egg or sperm only has one version of the gene.
   • For example, when you cross tall plants with short plants, you often see a ratio of 3 tall plants to 1 short plant in the next generation. This shows that the tall version of the gene hides the short version.

2. Law of Independent Assortment:

   • This law explains that different traits are inherited separately.
   • When looking at two or more traits at the same time, they mix together in new ways.
   • For instance, if you cross plants with different seed shapes and colors, you can see a mix of traits that results in a ratio of 9:3:3:1 in the next generation.

Key Terms:

• Genes: Parts of DNA that determine traits.
• Alleles: Different forms of a gene (like tall or short for a plant).
• Genotype: The actual genetic makeup of an individual (like TT, Tt, or tt).
• Phenotype: What you can see, or the traits that show up (like whether a plant is tall or short).

Using Probability in Mendelian Genetics:

• You can use a tool called a Punnett square to predict the chances of getting certain traits.
• If two plants that carry one of each gene version (Tt) are crossed, the genetic makeup possibilities are 1 TT, 2 Tt, and 1 tt. This means, when you look at what you can see, there’s a 3:1 chance of getting tall versus short plants.

In summary, Mendelian genetics helps us understand how traits like dominant and recessive traits are passed down from parents to their children. It also shows the variety of genes that can appear in different plants and animals.