Minggu, 02 Februari 2014

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The Correlation Between Modern Genetics and Mendelian Low I

Modern genetics identifies the heredity unit which is called Gene. The term of gene is what Mendel called as X factor at His time.

Hybridization technique in pea plant by mendel

Figure Hybridization technique in pea plant by mendel interprets Mendel's experiment in Tall stem trait inheritance of pea plant. Each trait in pea plant Is controlled by two alleles. An allele is an alternative form Of gene whose function is to control stem height. Dominant Allele of stem height is written by capital letter (T), while Recessive allele is written by lowercase letter (t). The alleles Line in homologous chromosome pairs at particular site called locus.

Homologous  chromosome  hastwo atlete  for every  trait (characteristic).

The result of chromosome observation shows that there are similarities Between Mendel's Law 1 and meiosis in modern genetics. The similarities Are show in the following matters.

  1. Meiosis occurs during gamete formation, and Mendel's law is also related to the process of gamete formation.
  2. In meiosis there occurs homologous chromosome conjugation, which is the same with the presence of a gene pair controlling one trait in plant. 
  3. Homologous chromosome will segregate and migrate to opposite poles, which is similar to segregation law.

In Mendel hybridization, parental (P generation) was the real breeding; The tall plant had two alleles for tall trait (TT), while the short plant had Two alleles for short trait (tt). A plant having identical allele is called Homozygous. Since the parental is homozygous, all gametes produced by Tall plant carry allele I while all gametes produced by short plant carry Allele. Both TT and, tt pairs are pure-breeding.

After the cross breeding is done, all the organisms of F, generations Have one allele for tall trait and one allele for short trait (Tt). When a plant Has two different alleles in one locus, we call it Heterozygous. Even though F1 generation has only one of each allele type, the plant resulted from the hybridization is tall. The allele expressed in heterozygous organism is called dominant allele. The one that is not expressed in heterozygous organism is called recessive allele. It is different from the case of homozygous since the heterozygous pair (Tt) is not pure-breeding.

In modern genetics, there are known the terms of genotype and phenotype. Genotype is the set of allele (gene) controlling an organism's appearance. For example, Genotypes for tall plant are TT, Tt, and tt. Genotype TT is called Dominant heterozygous, while genotype tt is called recessive Homozygous, and genotypeTt is called heterozygous.

Phenotype is the observable physical traits of an organism. For example, traits of tall and short (stem height), round or Wrinkle (seed shape), and purple or white (flower color).

Source:Biology. Concepts and connections, 2006

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