Imagine two loci, one codes for the pigment black and is dominant over the reces

Question

Imagine two loci, one codes for the pigment black and is dominant over the recessive condition, white. pigment, compared to its recessive condition, which also results in white. Using the law or probability, account for the return of a 12:3:1 ratio produced by crossing the dominant homozygous BBGG (green colored) with a tester, bbgg (white colored). The other locus is an epistatic dominant mutation that produces green Understand the three classes of mutational revertants. Explain skin color in relation to polygeny, pleiotropy, penetrance and expressivity. Distinguish between a qualitative and a quantitative trait.

Explanation / Answer

1. In dominant epistasis, one domiant gene of one allelic pair masks the actiivty of another dominant gene of another non allelic pair, which is an example of gene interactions. In class-I revertant, mutant codon is changed to same like that of original DNA code, which synthesises the proetin similar to wild type. In class-II revertant, one codon is changed to another codon which code for the same class of aminoacid at the same loci ( for example, one non polar aminoacid, valine (GUU) changed to another same class of non polar aminoacid alanine (GCU) due to mutation). In Class III revertant, reversion occurs when there is a stop codon produced by the initial mutation, and a second site suppressionevent happens.

2.Skin color is an example of polygene, i.e., more than one gene codes for the skin color. Pleiotrophy is a condition in which one gene codes for more than one phenotypic expression, ex: sickle cell anemia, phenyl ketonuria,etc. Penetrance gives the idea of proportion of individuals with a mutation that shows any evidence of disease, whereas expressivity gives the idea about degree of severity in individuals with a genetic disease.

3. In qualitative traits, phenotypes are with discrete and easily predectible or measure values (charecters), whereas quantitative traits in which individuals cannot be classified by discrete values..

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