How Genes Effect Our Appearance
In 1865, an Augustinian monk named Gregor Mendel discovered that individual traits are determined by discrete "factors," later known as "genes," which are inherited by the parents. While researching his new discovery, he found that genes come in pairs, and each gene has a trait with two alternate forms, such as the pea plant with it's green or yellow seeds. By analyzing the results of various crosses, Mendel concluded that each alternative form of a trait is specified by alternative forms of a gene. To follow the inheritance from parent to child, Mendel first needed to be sure which genes each parent carried. Since pea plants are naturally self-fertilizing, "pure-bred" strains were available. Upon closer look, Mendel discovered that each strain contained only one form of the gene that determined a trait. From the results of further experiments, Mendel theorized that pure-bred plants must have two copies of the same gene for each trait. In general, offspring appear to be a mixture of parental characteristics. However, Mendel found that this is not true for the pea plant traits that he chose to study. Pure-bred pea plants when crossed did not produce offspring with blended traits. For ex
ample, one might expect that when a pure-bred green-seeded and a pure-bred yellow-seeded pea plant were crossed their offspring would produce seeds with a green-yellow color. That, however, was not true for everytime only one color was produced: yellow. There were no blends present, and the green color disappeared. Mendel proposed that although both gene alternates are present, there is no blending of color because the gene alternate for yellow is dominant over the gene alternate for green. The dominant trait is seen only when a single copy of it's gene is inherited. When he crossed the hybrid offspring, green seeds reappeared in the next generation. Mendel theorized that the recessive green trait is shown only when a copy of the recessive green form is inherited from each parent. When Mendel proposed that each trait is determined by a pair of genes, it presented a potential problem. If parents pass on both copies of a gene pair, then offspring would end up with 4 genes for each trait. Mendel deduced that sex cells - sperm and egg - contain only one parental gene of each pair. The half-set of genes contributed by sperm and egg restore a whole set of genes in the offspring. Mendel found that different gene combinations in the parents resulted in specific ratios of dominant-to-recessive traits. The result of a cross between two hybrid parents
Some common words found in the essay are:
Gregor Mendel, Plant Hybridization, Effect Appearance, sex cells, homologous chromosomes, sperm egg, pea plant, reduction division, mendel theorized, dominant recessive, chromosomes determine, copies gene, gene trait,
Approximate Word count = 911
Approximate Pages = 4 (250 words per page double spaced)
|
