Genetics and Biotechnology

Grade 12 · Science · Study Guide

An exploration of heredity, gene expression, and modern biotechnological tools that manipulate genetic information.

Genetics is the science of heredity — how traits are transmitted from parents to offspring. DNA, organized into chromosomes, carries genetic information encoded in sequences of four nucleotide bases (A, T, G, C). Genes are specific DNA sequences that encode proteins or functional RNA molecules.

Gene expression involves two main stages: transcription (DNA → mRNA in the nucleus) and translation (mRNA → protein at ribosomes). Regulation of gene expression determines which genes are active in which cells and at which times — essential for development and cellular identity.

Mendel's laws describe inheritance patterns. The law of segregation states that alleles separate during gamete formation. The law of independent assortment states that alleles of different genes assort independently (unless linked). Non-Mendelian patterns include incomplete dominance, codominance, sex-linkage, and polygenic inheritance.

Biotechnology applies knowledge of genetics to practical problems. Recombinant DNA technology uses restriction enzymes and DNA ligase to cut and rejoin DNA from different sources. The polymerase chain reaction (PCR) amplifies specific DNA sequences exponentially. CRISPR-Cas9 is a programmable gene-editing tool derived from bacterial immune systems, capable of making precise cuts in the genome. These tools underpin medicine, agriculture, forensics, and biofuel production.

Key terms

Allele
One of two or more alternative forms of a gene that can occupy the same locus on homologous chromosomes.
Transcription
The synthesis of mRNA from a DNA template, catalyzed by RNA polymerase in the nucleus.
CRISPR-Cas9
A bacterial-derived gene-editing system using guide RNA to direct the Cas9 nuclease to cut specific DNA sequences.
Restriction enzyme
A bacterial enzyme that cuts DNA at specific recognition sequences; used in recombinant DNA technology.
Genotype
The specific allele combination an organism possesses for a given gene or set of genes.
Epigenetics
Heritable changes in gene expression that do not involve changes to the DNA sequence, often mediated by methylation or histone modification.

Flashcards

Locus
The specific physical location of a gene or DNA sequence on a chromosome.
Meiosis
Cell division that reduces chromosome number by half, producing haploid gametes with unique genetic combinations.
Codon
A three-nucleotide sequence in mRNA that specifies a particular amino acid or a stop signal during translation.
Recombinant DNA
DNA molecules assembled from sequences derived from two or more different organisms using molecular biology tools.
Plasmid
A small, circular, self-replicating DNA molecule in bacteria, used as a vector in recombinant DNA technology.
Gel electrophoresis
A technique that separates DNA, RNA, or proteins by size as they migrate through a gel matrix under an electric field.
Pedigree
A diagram showing the inheritance pattern of a trait across multiple generations of a family.
Frameshift mutation
An insertion or deletion of nucleotides that shifts the reading frame of the mRNA, altering all downstream amino acids.

Questions

  1. Which enzyme is responsible for joining Okazaki fragments during DNA replication?

    1. DNA polymerase III
    2. Primase
    3. DNA ligase
    4. Helicase
    Show answer

    Answer: DNA ligase

    DNA ligase seals the nicks between Okazaki fragments on the lagging strand by forming phosphodiester bonds, completing the new strand.

  2. In codominance, the heterozygous phenotype is an intermediate blend of both homozygous phenotypes.

    Show answer

    Answer: False

    Codominance occurs when both alleles are fully expressed simultaneously (e.g., AB blood type); incomplete dominance produces an intermediate blend.

  3. The PCR technique requires a thermostable DNA polymerase called _____ polymerase.

    Show answer

    Answer: taq

    Taq polymerase, isolated from Thermus aquaticus bacteria that live in hot springs, withstands the high temperatures (95°C) of the denaturation step in PCR.

  4. Which process correctly describes the central dogma of molecular biology?

    1. RNA → DNA → Protein
    2. DNA → RNA → Protein
    3. Protein → RNA → DNA
    4. DNA → Protein → RNA
    Show answer

    Answer: DNA → RNA → Protein

    The central dogma states that genetic information flows from DNA (via transcription) to RNA and then (via translation) to protein; reverse transcriptase is an exception.

  5. A test cross is performed to determine:

    1. The number of chromosomes in an organism
    2. Whether an organism showing the dominant phenotype is homozygous or heterozygous
    3. The frequency of recombination between two loci
    4. The degree of incomplete dominance
    Show answer

    Answer: Whether an organism showing the dominant phenotype is homozygous or heterozygous

    A test cross breeds the organism with an unknown genotype against a homozygous recessive; all offspring showing the recessive phenotype reveals the parent was heterozygous.

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