Since homozygous dominant and heterozygous display the same phenotype, 75 percent of the F2 generation will express the dominant – or wild type – trait, and 25 percent will express the recessive trait the ratio is 3:1. If two of those heterozygous individuals are mated, 25 percent of the resulting F2 generation will be homozygous dominant, 50 percent will be heterozygous, and 25 percent will be homozygous recessive the ratio is 1:2:1. In a simple cross between a homozygous dominant parent and a homozygous recessive parent, all the F1 offspring will be heterozygous – each will have one dominant and one recessive copy of the gene – and the phenotype will be the dominant trait.
It is able to express itself even in the presence of its recessive allele. The first generation of offspring is called F1, and the next generation is F2, etc. Differences between Dominant and Recessive Genes in Inheritance 1. Punnet squares are graphs representing the genotypes that would hypothetically result from a cross of parents of known genotype. On the other hand, a recessive trait only affects an individual if he has two identical – homozygous – copies of that gene. A dominant trait is expressed (phenotype) whenever that allele is present, whether homozygous or heterozygous (genotype). The combination of genes results in the phenotype, the actual observable trait. Homozygous and heterozygous describe the genotype. Let us understand this by a simple example. However, recessive traits are those that are expressed only when two copies of an allele are present in the gene. An individual is homozygous for a particular gene if he has two identical versions of that gene whereas, he is heterozygous if he has two different versions of that gene. Dominant traits are those traits which are expressed even in the presence of one copy of an allele for a particular trait in the gene. Mendelian traits – the characteristics studied by Gregor Mendel – are determined by a single gene.
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