Biology - Genetics and Molecular Biology (DNA, Inheritance, and Biotechnologies)

In a sample of double-stranded $DNA$, $22\%$ of the nitrogenous bases are Cytosine ($C$). Calculate the percentage of Adenine ($A$) in this sample.

1. If $[C] = 22\%$, then $[G] = 22\%$ because $[C] = [G]$.
2. Total $C + G = 22\% + 22\% = 44\%$.
3. The remaining percentage for $A + T$ is $100\% - 44\% = 56\%$.
4. Since $[A] = [T]$, then $[A] = \frac{56\%}{2} = 28\%$.

Chargaff's rule states that $DNA$ base pairs are stoichiometric. Since $C$ pairs with $G$ and $A$ pairs with $T$, their percentages must be equal respectively, and all four must sum to $100\%$.

A pea plant is heterozygous for seed shape ($Rr$), where Round ($R$) is dominant over wrinkled ($r$). If this plant is crossed with a wrinkled-seeded plant ($rr$), what is the probability of producing a round-seeded offspring?

1. Parent genotypes: $Rr \times rr$.
2. Possible gametes: Parent 1 ($R, r$); Parent 2 ($r, r$).
3. Punnett Square results: $Rr, Rr, rr, rr$.
4. Probability of Round ($Rr$) = $\frac{2}{4} = 50\%$.

A test cross between a heterozygote and a homozygous recessive individual results in a $1:1$ ratio of dominant to recessive phenotypes.

Describe the movement of $DNA$ during Gel Electrophoresis.

$DNA$ molecules have a negative charge due to their phosphate groups ($PO_4^{3-}$). In an electric field, they migrate towards the positive electrode. Smaller fragments encounter less resistance from the gel matrix and travel further than larger fragments.

Separation is based on the inverse relationship between fragment size and migration distance: $Distance \propto \frac{1}{\text{log(Size)}}$.