The Stubborn Gene

SO HOW MENDEL GOT ENLIGHTENED?

Mendel realized that there are specific factors - later to be called "genes" - that are passed from parent to offspring. He worked out that these factors come in pairs and that the offspring receives one factor from each parent.

Noticing that peas come in two distinct colors, green and yellow, he deduced that there were two versions of the pea color gene - Y and G - later to be called "alleles". Each parent has a gene that contains a pair of such alleles - in form of either YY (Yellow), YG (Yellow) or GG (Green) - Now how did he say this so confidently? I will tell you why - Mendel crossed a green pea plant with a green pea plant - the result was always a green pea plant (no matter how many generations) but when he crossed a yellow pea plant with a yellow pea plant - the result was a yellow pea plant in the first generation or may be in the second generation too but a green pea plant always use to show up once in a while in the concluding generations. He hypothesized that green version is a recessive version since it needs to be always self fertilized to get a green offspring. Though, it can also get carried away for generations without showing up. Yellow, on the other hand, is the dominant version of a pea plant. It is prevalent, since when he crossed a yellow plant with a green one - the result was either always yellow in the first generation and same in the second generation or sometimes green color used to show up in the first generation itself - in this case - the yellow plant must have been a heterozygous - YG - carrying a green version (G allele) of the color gene.

Thus he concluded that the Green color is the recessive version of pea plant though tends to show up no matter how much you try not to get it; Yellow color on the other hand is dominant version, more prevalent in nature. In order to ease up his mind, he started showing up the heterozygous or homozygous gene pairs as Yy or yy/YY respectively, where 'Y' represents the dominant yellow allele and 'y' represents the recessive gene allele.

Each and every organism which born on the basis of sexual reproduction is either a homozygous or a heterozygous. Albinism is related with the recessive version of the gene that produces skin pigment - melanin. Now just like the Green pea that we prefer to eat, if one prefers an albino to born, both the parents must be an albino but no matter how much we try to avoid, an albino may always show up in one's concluding generations. When a gene is recessive, an individual has to have two copies of it for the corresponding trait to be expressed. Those individuals with a single copy are carriers: they don't themselves exhibit the characteristics, but they can pass the gene on. Therefore, to be albino you have to have two copies of the gene, one from each parent.

Everything was clear, hair color inheritance, eye color, height etc. but the scientific community did not accept it; Apparently, Darwin though living almost in the same era did not got aware of Mendel's work.

Check out the following video for easier understanding of the above concept: -