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Genetics - Genetic modification and biotechnology

Grade 12IBBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Gel electrophoresis is used to separate proteins or fragments of DNA according to size and charge. DNA molecules are negatively charged and migrate towards the positive electrode (anode).

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PCR (Polymerase Chain Reaction) is used to amplify small amounts of DNA. The process involves three temperature-dependent stages: Denaturation at ≈95∘C\approx 95^\circ C, Annealing at ≈55∘C\approx 55^\circ C, and Elongation using TaqTaq polymerase at ≈72∘C\approx 72^\circ C.

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DNA profiling involves the comparison of DNA. In IB Biology, this often focuses on Short Tandem Repeats (STRsSTRs), which are non-coding regions of DNA that vary in length between individuals.

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Genetic modification is carried out by gene transfer between species. This is possible because the genetic code is universal; for example, the codon AUGAUG codes for Methionine in nearly all organisms.

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Gene transfer to bacteria involves using restriction endonucleases to cut DNA at specific sequences (forming 'sticky ends'), and DNADNA ligase to join the target gene into a plasmid vector.

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Genetically modified organisms (GMOsGMOs) like BtBt corn contain a gene from Bacillus thuringiensis that produces a toxin to kill pests, reducing the need for chemical insecticides but raising concerns about non-target species like Monarch butterflies (DanausDanaus plexippusplexippus).

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Clones are groups of genetically identical organisms, derived from a single original parent cell. Somatic Cell Nuclear Transfer (SCNTSCNT) is a method used to produce cloned embryos by replacing the nucleus of an unfertilized egg with a diploid nucleus from a differentiated somatic cell.

📐Formulae

N=2nN = 2^n

P=(14)nP = (\frac{1}{4})^n

v=qEfv = \frac{qE}{f}

💡Examples

Problem 1:

A scientist starts a PCR reaction with 55 double-stranded DNA molecules. Calculate the total number of DNA molecules present after 2525 complete cycles of amplification.

Solution:

N=5×225=167,772,160N = 5 \times 2^{25} = 167,772,160

Explanation:

The number of DNA molecules doubles with every cycle. The formula used is N=N0×2nN = N_0 \times 2^n, where N0N_0 is the initial number of molecules (55) and nn is the number of cycles (2525).

Problem 2:

In DNA profiling, if the probability of a specific STRSTR allele occurring in a population is 0.100.10, and a profile uses 44 such independent STRSTR loci, what is the probability of another random person having the exact same profile?

Solution:

P=(0.10)4=0.0001P = (0.10)^4 = 0.0001 or 1×10−41 \times 10^{-4}

Explanation:

Since the loci are independent, the product rule of probability is applied. The individual probabilities are multiplied together to find the frequency of the total genotype.

Problem 3:

Identify the tools required to create a recombinant plasmid containing a human insulin gene (C257H383N65O77S6C_{257}H_{383}N_{65}O_{77}S_{6}).

Solution:

  1. Restriction endonucleases (to cut the gene and plasmid). 2. DNADNA ligase (to join the sugar-phosphate backbones). 3. E.coliE. coli plasmids (acting as the vector).

Explanation:

Restriction enzymes create compatible 'sticky ends' through complementary base pairing, while ligase facilitates the formation of covalent phosphodiester bonds.