explain the result of Mendel monohybrid cross
Answers
Monohybrid Cross
For monohybrid cross, Mendel began with a pair of pea plants with two contrasting traits i.e., one tall and another dwarf. The cross-pollination of tall and dwarf plants resulted in tall plants. All the hybrid plants were tall. He called this as a first hybrid generation (F1) and offspring were called Filial1 or F1 progeny. He conducted an experiment with all the seven contrasting pairs. He observed that the entire F1progeny showed one pattern in their behavior i.e., they resembled either one of the parents. Another parent character was completely absent.
Fig.1.
He continued his experiment with self-pollination of F1 progeny plants. Surprisingly, he observed that one out of four plants were dwarf while other three were tall. The tall and the short plants were in the ratio of 3:1. He also noted that no progeny was in intermediate height i.e., no blending. The result was same for other traits of plants too. And he called them second hybrid generation and offspring were called Filial2 or F2 progeny.
Fig.2
Mendel observed that traits were absent in F1 generation had reappeared in F2 generation. He called such suppressed traits as recessive traits and expressed traits as dominant traits. He also concluded that some ‘factors’ are inherited by offspring from their parent over successive generations.
Later, these ‘factors’ were called genes. Genes are responsible for the inheritance of traits from one generation to another. Genes consist of a pair of alleles which code for different traits. If a pair of alleles is same i.e., TT or tt, such alleles are called homozygous pair while those that are different or non-identical (e.g. Tt) are called heterozygous pair.
The cross between two monohybrid traits (TT and tt) is called monohybrid cross. Monohybrid cross is responsible for the inheritance of one gene. It can be easily shown through a Punnett Square.
Explanation:
Mendel carried out breeding experiments in his monastery’s garden to test inheritance patterns. He selectively cross-bred common pea plants (Pisum sativum) with selected traits over several generations. After crossing two plants which differed in a single trait (tall stems vs. short stems, round peas vs. wrinkled peas, purple flowers vs. white flowers, etc), Mendel discovered that the next generation, the “F1” (first filial generation), was comprised entirely of individuals exhibiting only one of the traits. However, when this generation was interbred, its offspring, the “F2” (second filial generation), showed a 3:1 ratio- three individuals had the same trait as one parent and one individual had the other parent’s trait.
Mendel then theorized that genes can be made up of three possible pairings of heredity units, which he called ‘factors’: AA, Aa, and aa. The big ‘A’ represents the dominant factor and the little ‘a’ represents the recessive factor. In Mendel’s crosses, the starting plants were homozygous AA or aa, the F1 generation were Aa, and the F2 generation were AA, Aa, or aa. The interaction between these two determines the physical trait that is visible to us.
Mendel’s Law of Dominance predicts this interaction; it states that when mating occurs between two organisms of different traits, each offspring exhibits the trait of one parent only. If the dominant factor is present in an individual, the dominant trait will result. The recessive trait will only result if both factors are recessive.
Mendel’s Laws of Inheritance
Mendel’s observations and conclusions are summarized in the following two principles, or laws.
Law of Segregation
The Law of Segregation states that for any trait, each parent’s pairing of genes (alleles) split and one gene passes from each parent to an offspring. Which particular gene in a pair gets passed on is completely up to chance.
Law of Independent Assortment
The Law of Independent Assortment states that different pairs of alleles are passed onto the offspring independently of each other. Therefore, inheritance of genes at one location in a genome does not influence the inheritance of genes at another location.