Molecular Biology Online Tutorials

Gregor Mendel is the Father of Transmission Genetics

Mendel describes what he called the conttribution of "particulates" from each parent to the child. Today we call these particulates - genes. In addition, through careful observation of each pea plant's offspring, Mendel was able to describe them based on physical characteristics. These characteristics are called the phenotype.

The phenotype can also be applied to more than one characteristic at a time, thus it is used to describe the organism as a whole, and not just one notable characteristic - such as eye color.

Mendel observed that a gene can exist in different forms called alleles. The pea plant can have either green or yellow seeds. One allele codes for green seeds and one allele codes for yellow seeds. In addition, he also observed that one allele can be dominant or recessive.

Dominant alleles will code over recessive alleles and mask certain phenotypes. Mendel demonstrated that the yellow seed was dominat over the green seed by crossing a plant that produced yellow seeds with a plant that produced green seeds. The first generation of plants (F1 generation) all produced yellow seeds.

He took it one step further and allowed those F1 plants to self fertilize and reproduce (F2 generation), then he noted that even though both parents produced yellow seeds, some green seeds reappeared in the second generation (F2). This led to a very important conclusion: That the gene for the green seed was not wiped out, it was only masked by the gene for the yellow seed. The green seed gene had been preserved!

He further concluded that each parent plant must have contained two copies of the gene - the parents were diploid. If both copies were the same (both yellow producers or both green producers) - that was termed homozygous. If the parent contained one copy of each, (one gene that coded yellow and one gene that coded green) then that was termed heterozygous.

Additionally, Mendel determined that sex cells, or germ cells, only contain ONE copy of the gene. That is called haploid. Sex cells that are homozygous can only produce one phenotype, but sex cells that contain one copy of each, or are heterozygous, are able to produce both possible phenotypes under the right circumstances. Go watch this video to learn the complete story of Mendellian Genetics

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