Question

Some genomic representation of skin colour are given below
i. AA bb CC
ii. AA bb cc
iii. AA BB CC
iv. Aa bb cc
Which of the options is correct for showing the darkness of colour of the skin in decreasing order?
A. iii $\Rightarrow$ ii $\Rightarrow$ I $\Rightarrow$ iv
B. i $\Rightarrow$ iv $\Rightarrow$ ii $\Rightarrow$ iii
C. iii $\Rightarrow$ i $\Rightarrow$ ii $\Rightarrow$ iv
D. i $\Rightarrow$ iii $\Rightarrow$ ii $\Rightarrow$ iv

Answer 1

Dark pigmentation is dominated by three "dominant" capital letter genes (A, B and C) so more melanin is made. Since lower levels of melanin are formed, the "recessive" alleles of these three genes (a, b & c) regulate light pigmentation.

Complete Answer:
Human skin colour is a polygenic inheritance that produces melanin pigment in three pairs of polygenes A, B and C, which induces human skin colour. Skin colour is regulated in humans by more than 1 gene.

Now, let us find the solution from the options-
- There would be the darkest skin colour out of the 64 offspring, followed by a number of middle shades from dark to bright, as there is a self-cross between AaBbCc. The highest volume of melanin and very dark skin has a genotype of all "dominant" AABBCC capital genes. A genotype has the lowest level of melanin and very light skin for all "recessive" aabbcc small case genes. The darkest of all will be AABBCC, followed by AAbbCC, then AAbbcc and Aabbcc.
- Aabbcc has the lowest level of melanin in the human genotype and has very light skin. If the human skin colour genotype is AAbbcc and AaBbcc respectively, light brown and dark brown are the phenotypes of these genotypes. Just one dominant allele A is found in genotype AAbbcc. Two alleles, A and B, are dominant in the AaBbcc genotype.

Thus, the correct answer is option C.

Note: One of the most striking manifestations of human phenotypic variability is skin colour variance. It is controlled by melanin, a pigmentation found in the base of the epidermis and formed by melanocytes. There are two types of melanin, eumelanin (black-brown) and pheomelanin (yellow-reddish).