Genetics and Genetic Engineering: DNA, Inheritance and Recombinant Technology
Genetics and Genetic Engineering tests inheritance from DNA to populations and the controlled manipulation of genetic material. Expect DNA structure, protein synthesis, meiosis, monohybrid and sex-linked crosses, mutation, and recombinant DNA technology.
DNA and inheritance
- DNA double helix: sugar-phosphate backbone, complementary base pairing A-T, C-G; hydrogen bonds between bases.
- Gene → transcription in nucleus → mRNA → translation at ribosome → polypeptide. Codon triplet; tRNA anticodon.
- Meiosis halves chromosome number; crossing over in prophase I and independent assortment in metaphase I create variation.
- Monohybrid cross: use letters, state parental genotypes, gametes, Punnett square, phenotype ratio.
Genetic engineering
- Steps: isolate gene (restriction enzyme), insert into vector (plasmid) using DNA ligase, transfer into host, select and clone. Examples: insulin-producing bacteria, GM crops, gene therapy.
- Mutation: substitution, insertion, deletion; can be harmful, neutral or beneficial.
Worked example: Cross heterozygous tall pea (Tt) with short (tt). Gametes T/t × t/t; offspring Tt and tt in 1:1; 50% tall, 50% short. Reasoning: short parent must be tt because short is recessive; ratio is not 3:1 because one parent is homozygous recessive.
Traps: dominant allele is not necessarily more common; genotype vs phenotype; meiosis produces four haploid cells, mitosis two diploid; sex-linked traits more common in males because one X; genetic engineering does not make genes from nothing.