Biology Tutorials > Genetics and Evolution > Crossing Over and Genetic Diversity

Crossing Over and Genetic Diversity

Crossing Over and Genetic Diversity

Laws on Mendelian inheritance were based on garden pea plant experiments of Gregor Mendel.

Gregor Mendel, an Austrian monk, is most famous in this field for his study of the phenotype of pea plants, including the shape of the peas on the pea plants.

Gregor Mendel’s Work

Mendel’s goal was to have a firm scientific basis on the relationship of genetic information passed on from parents to offspring. In light of this, he focused on how plant offspring acquired the phenotype of their seeds. In this example, there are two choices, round and wrinkled seeds.

The plants that were used in the experiment had to be true breeding, i.e. those plants with round seeds must have had parents with round seeds, who in turn had parents producing round seeds, etc. This is done to increase the accuracy of the results.

After successfully producing two generations from these true-breeding plants, the following was evident

  • The first generation of plants produced all had a round seed phenotype.
  • When these first-generation plants were crossed, a ratio of 3 round seeds averaged every 1 wrinkled seed.
  • The ratio of 3:1 was not exact, though this is because of the randomness of the processes that are executed to produce these plants. For example, the independent assortment is completely random, as are mutations, therefore variable results occur producing a sampling error.
  • Due to the scale of the experiment done by Gregor Mendel, the sampling error was smaller than that of a smaller scale experiment.

Mendel successfully hypothesized that the reason for this trend in phenotypes from generation to generation was down to the fact that genetic information was being passed on from their parents.

The fact that round seeds appeared more frequently than wrinkled seeds is due to round seeds being the dominant phenotype, which when present effectively ‘masks’ the phenotype of the recessive (wrinkled seed) gene.

Dominant and Recessive Alleles

  • All plant seeds produced in the first generation were round
  • 3 out of every 4 plant seeds produced in the second generation were round

The parents, one possessing wrinkled seeds the other possessing round were crossed together, for some reason in the first and second generation the presence of the round seed gene in offspring superseded the presence of the wrinkled seed. This is called dominance.

The next tutorial investigates this dominance, and how it can successfully be predicted. It also has examples of a monohybrid and dihybrid cross.

Fun activity: Simple Genetics Practice Problems

 

Biology Tutorials > Genetics and Evolution > Crossing Over and Genetic Diversity

You will also like...

Schematic diagram of bacterial lactose operon
Gene Action – Operon Hypothesis

This tutorial focuses on the way genes control and determine every aspect of the body. It describes lac operon as an exa..

kinesin motor proteins transporting molecules across microtubules
Movement of Molecules Across Cell Membranes

Molecules move within the cell or from one cell to another through different strategies. Transport may be in the form of..

Salmon jumping upstream in the river
Lotic Communities & Animals

A running water environment offers numerous microhabitats for many types of animals. Similar to plants, animals in lotic..

Genetics and Evolution
Genetics and Evolution

Tutorials in Genetics and Evolution immerse on the molecular aspects and the works of nature that led to what every livi..

Photosynthesis and respiration
Plant Metabolism

Plants are responsible for incredible feats of molecular transformation. Plant processes, such as photosynthesis, photop..

Growth Patterns
Growth Patterns

This tutorial describes the sigmoid curve, annual plant growth, tree growth, human growth, and insect growth as the grow..