Explain monohybrid inheritance including co-dominance - Assignment Example

Monohybrid inheritance and co-dominance Monohybrid inheritance is an inheritance pattern in which two animals or two plants being crossed in an experiment are identical genetically except for one single heterozygous gene. That is to say, inheritance is passing parental characteristics to offspring, while monohybrid inheritance is that inheritance for one characteristic. Monohybrid inheritance entails a cross between two parents possessing different forms of a gene (alleles) referred to as monohybrid inheritance.

Parental characteristics passed in this manner are primarily determined by genes existing in form of alleles. Because plant and animal chromosomes exist in matching pairs in each cell’s nucleus, there will often be two genes for a particular characteristic in a cell. Where the same allele appears twice, then the organism is referred to as homozygous for this particular characteristic. However, in cases where one chromosome has one allele contrasting from the allele in the other chromosome, then the organism is referred to as heterozygous for that particular characteristic.

In heterozygous organisms, the organism’s (phenotype) appearance may be determined by a single allele and not the other allele. This allele that determines this particular phenotype is referred to as dominantly expressed allele, however, the expression of the other allele is said to be recessive (Campbell, 2006). In general foundations, monohybrid cross are applied in determining F2 generation from homozygous pair of grandparents (one grandparent recessive, the other dominant). This leads to an heterozygous F1 generation.

However, crossing two parents who are heterozygous from F1 generation results into F2 generation producing 75% chance for the dominant phenotype appearance, from which two thirds are particularly heterozygous, and 25% chance for recessive phenotype appearance. This form of cross was initially used by Gregor Mendel who did an experiment on two plants and obtained a variety of hybrid; he discovered the possible changes in the allele phenotypes (Campbell, 2006).On the other hand, co-dominance is when the genes (alleles) are only expressed in an individual.

Blood groups are a good example. Blood groups B and A are totally dominant to blood group O, but they are co-dominant to each other. In co-dominance, a single gene entails more than just one allele. Therefore a heterozygous individual for twp co-dominant alleles expresses the phenotypes that are associated with both alleles. That is to say, a situation where two distinct alleles for a particular gene are both expressed. In monohybrid inheritance if alleles are different, the dominant allele will often be expressed and the effect of the recessive allele is masked.

However, in co-dominance, there is no recessive or dominant allele, and therefore both the allele’s phenotypes are expressed. It is important to note that semi or incomplete dominance is not the same thing as co-dominance. For example, in particular species of plants, red and white spotted flowers may be as a result of co-dominance between the white allele for the gene and the red allele for the gene (specifically co-dominance at the level of pigment and no dominance at the level of color), or the product of non-functional allele producing no pigment and one allele producing normal amount red pigment, in order to produce intermediate dilute pink color (no particular dominance at either of the levels) (Campbell, 2006).

BibliographyCampbell, Neil A. 2006. Biology: concepts & connections. London: Pearson Benjamin Cummings.