# Tutor profile: Sanjana K.

## Questions

### Subject: Biology

In a tribal African population, 16% of individuals are born with sickle cell anemia (aa). What then is the percentage of individuals who are conferred with the selective advantage of the sickle-cell gene with respect to Malaria?

The individuals that are heterozygous (Aa) and are therefore carriers of the sickle cell trait are conferred with the selective advantage of increased resistance to malaria. The shape of the cell membrane in these heterozygous individuals inhibits the plasmodium parasite from infecting the body. The frequency of these individuals is represented by the term $$2pq$$ in the commonly used Hardy-Weinberg equation: $$p^2+2pq+q^2=1$$, with the condition that $$p+q = 1$$ In this equation, $$p^2$$ represents the dominant homozygous frequency (AA), $$q^2$$ represents the recessive homozygous frequency (aa), and $$2pq$$ represents the heterozygous frequency (Aa). We are told that 16% of the population is affected with sickle cell anemia, so we know that $$q^2 = 0.16$$ Therefore, $$q=\sqrt{0.16}=0.4$$ From the condition $$ p+q = 1$$ we can find $$p =0.6$$ It can then be concluded that the allele 'A' has a frequency of 0.6 and the allele 'a' has a frequency of 0.4. Therefore, the percentage of the population that is heterozygous (Aa) and are carriers is: $$2pq=2×0.4×0.6=0.48$$ Therefore the percentage of individuals who are conferred with the selective advantage is 48%.

### Subject: Electrical Engineering

A series circuit with a resistance of 10 Ohms, Inductance of 0.2 H and capacitance of 40 micro farads is supplied with a 100V supply at 50Hz. Find current, power, and power factor.

Circuit resistance, $$R = 10\Omega$$ Inductive reactance of the circuit, $$X_{L}= 2ΠfL =2Π × 50 × 0.2 = 62.83 Ω$$ Capacitive Reactance of the circuit, $$X_{C} =\frac{1}{2ΠfC} = \frac{1}{2Π ×50×40×10-6} = 79.57 Ω$$ Impedance of the circuit, $$Z = \sqrt{(R^2+(X_L – X_C )^2 )}= \sqrt{(10^2+(79.57-62.83)^2 ) }$$ $$Z= √(100+280.2)=19.5 Ω$$ Circuit Current, $$I = \frac{V}{Z}=\frac{100}{19.5} = 5.131A$$ Circuit power factor, $$cos(Φ) = \frac{R}{Z} = \frac{10}{19.5} =0.513$$ Power Consumed, $$P = VIcos(Φ)= 100 × 5.131 × 0.513 = 263.2 $$ Watts Therefore, the circuit current is 5.131 Amperes, the power factor is 0.513, and the power consumed by the circuit is 262.2 Watts.

### Subject: English

You see the following excerpt taken from your favorite short story: Why does he go to the bakery? Because he likes to eat cake. Is this acceptable in written English?

The excerpt is permissible in spoken English, but not in written English. This is because it contains a sentence fragment (an incomplete sentence). A sentence must have at least one main or independent clause which contains a subject and a verb. In contrast, a dependent clause usually begins with a conjunction (e.g.: if, when, because, after, etc.). This means that it cannot stand on its own and must be attached to an independent clause. In this case, ‘Because he likes to eat cake’ is the sentence fragment. Now, we can attach the sentence fragment to the independent clause as follows: ‘He goes to the bakery because he likes to eat cake.’ It is important to avoid sentence fragments in written English as this is grammatically incorrect and also detracts from the flow of one’s writing.

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