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what is a monohybrid cross illustrate with an example
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Monohybrid Cross Definition. A monohybrid cross is a genetic mix between two individuals who have homozygous genotypes, or genotypes that have completely dominant or completely recessive alleles, which result in opposite phenotypes for a certain genetic trait.
Flower color: Violet/white
Flower position: Axial/terminal
Pod color: Green/yellow
Pod shape: Inflated/constricted
Seed color: Yellow/green
Seed shape: Round/wrinkled
Stem height: Tall/dwarf
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.
Refer fig1
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.
Refer Fig2.
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.
Examples:
1.Example: The Fishbaums. Let's look at an example of a monohybrid cross, demonstrated by Fred and Rita Fishbaum (any similarity to living or dead fish is purely coincidental). They are monohybrids, so they each have one dominant allele and one recessive allele.
Refer Fig3.
2.example
Refer fig4.
