Rabu, 27 November 2013 0 komentar
Firstly, Mendel studied the inheritance of seed shape. The hybridization involving only one distinct trait is called monohybrid cross. Parental is symbolized by P1, generation (first parental). The crossing (hybridization) result between parental is called hybrid and symbolized by generation (first filial). The seed of F1, is grown and becomes F1, plant. The characteristics of F1, generation can be looked at
THE OFFSPRING OF F1, GENERATION
Moreover, the F1, generation plants undergo self-pollination And produce seeds of F2, generation. The ratio of F2, generation. (Second filial or the ratio of F2 or the crossing result between F1, generation) is 3 : 1. The characteristics of F, can be looked at Table.
THE OFFSPRING OF F2, GENERATION
When pure-breeding tail stem plants crossed with short stem plant, all of the offspring produced are tall stem plants. The tall stem trait that appears is considered as dominant, while short stem trait is recessive. This principal is known as (dominancy law.)
Dominant trait is a trait that covers up another trait. Recessive trait is a trait that is suppressed by dominant trait. The trait wiII appear if there is no dominant trait. Mendel used capital letter to symbolize dominant trait and lowercase letter to symbolize recessive trait. The plants in Mendel's experiment showed full dominancy because therewas no intermediate trait appearing in the offspring. It means, there will be no rather tall (intermediate trait between tall and short traits) in the offsprings.
Based on the experiment, Mendel composed some hypotheses, which are as follows.
- There are dominant-recessive correlation between factors of trait determiner (dominancy law).
- Heredity factors are segregated during gamete formation and each gamete only carries one copy of each factor.
- Gamete conjugation occurs randomly.
Based on the above hypotheses, Mendel's Law I, which is Know as segregation law, was discovered. Segregation law
Monohybrid cross by observing
Monohybrid cross and segregation
State that during gamete formation there occurs the process Of segregation or segregation of heredity factors randomly. Therefore, each gamete only carries one factor for each trait.
To test the hypothesis on allele segregation (modern understanding) which stated that F1 was heterozygous, Mendel crossed F, generation with homozygous recessive plant (short). Reason was that half of the offspring (F2) was supposed to be Tall and the other half was short so that it would create phenotype Ratio of 1 : 1. And actually the test result supported Mendelian Segregation law. The cross between an unknown organism with Recessive homozygous organism is known as testcross.
One exampte of testcross
In the early 1900, R.C. Punnet introduced a method to describe Generation probabilities resulted from genetic hybridization. In this case, Punned used a square diagram (chess board). The diagram is later known As Punnet square.
Punnet diagram, a method to describe genetic hybridization
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