Imagine a population (with individuals of all possible genotypes) whose food supply is sometimes contaminated with a poison that tastes like PTC. Anyone who cannot taste PTC eats the food and dies. The survivors, the PTC tasters, reproduce. Will be there anyone in this new generation that CANNOT taste PTC? Why?
Imagine a population (with individuals of all possible genotypes) whose food supply is sometimes contaminated with a poison that tastes like PTC. Anyone who cannot taste PTC eats the food and dies. The survivors, the PTC tasters, reproduce. Will be there anyone in this new generation that CANNOT taste PTC? Why?
Humans possess two types of chromosomes: autosomes and sex chromosomes. Some of the physiological or behavioral traits are linked to autosomes, known as an autosomal trait and others are linked to sex-chromosomes, known as a sex-linked trait.
PTC (phenylthiocarbamide) is a bitter compound and bitter taste is determined due to the presence of the taste receptor gene (TAS2R38), which is an autosomal gene. Thus, PTC tasting is a bimodal autosomal trait. Individuals that possess the TAS2R38 gene in homozygous condition will have strong taste buds for PTC, the heterozygous individual will have slightly weaker taste receptors, and those that do not possess this gene cannot taste PTC.
It is provided that the population contains all possible genotypes of the PTC gene. Let's represent the person containing the PTC gene as TB and the person not containing the PTC gene as T.
Thus, possible genotypes of the population are homozygous dominant (TB TB), heterozygous (TBT), and homozygous recessive (TT). Homozygous dominant and heterozygous individuals can taste PTC, while homozygous recessive individuals cannot taste PTC.
Cross between homozygous dominant individuals.
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|
TB |
TB |
|
TB |
TB TB (Can taste) |
TB TB (Can taste) |
|
TB |
TB TB (Can taste) |
TB TB (Can taste) |
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