Unit 4 Study Guide: Genetics, Protein Synthesis, and Immunology

Genetics, Protein Synthesis, and Immunology

Key Terms and Definitions

This section introduces essential vocabulary for understanding genetics, protein synthesis, and immunology. Mastery of these terms is foundational for further study in biology.

• Genetics: The scientific study of heredity and variation in living organisms.

• Protein Synthesis: The process by which cells build proteins based on genetic instructions, involving transcription and translation.

• Immunology: The branch of biology concerned with the immune system and immune responses.

• Trait: A specific characteristic of an organism, such as flower color or height.

• Allele: Different forms of a gene found at the same locus on homologous chromosomes.

• Dominant: An allele that masks the effect of a recessive allele in heterozygous individuals.

• Recessive: An allele whose effect is masked by a dominant allele; only expressed in homozygous individuals.

• Heterozygous: Having two different alleles for a particular gene (e.g., Rr).

• Homozygous: Having two identical alleles for a gene (e.g., RR or rr).

• Genotype: The genetic makeup of an organism (e.g., Rr, RR, rr).

• Phenotype: The observable traits of an organism resulting from genotype and environment.

• Codon: A sequence of three mRNA nucleotides that codes for a specific amino acid.

• Anticodon: A sequence of three tRNA nucleotides complementary to an mRNA codon.

• Complementary Base Pairs: Specific pairing of nitrogenous bases (A-T/U, C-G) in DNA and RNA.

• Mutagen: An agent that causes mutations in DNA.

• Mutagenesis: The process by which genetic mutations are generated.

• Recombinant DNA: DNA molecules formed by combining genetic material from different sources.

• Clone: An organism or cell produced asexually from one ancestor, genetically identical to it.

• Inflammatory Response: A non-specific defense mechanism involving swelling, redness, and heat at the site of injury or infection.

• Perforin: A protein released by cytotoxic T cells that creates pores in target cell membranes.

• Autoimmune Disease: A condition in which the immune system attacks the body's own tissues.

• Immunodeficiency Disease: A disorder in which the immune system's ability to fight infectious disease is compromised.

• Allergies: Hypersensitive immune responses to harmless substances.

Comparisons and Key Differences

Understanding the distinctions between related concepts is crucial for mastering genetics, protein synthesis, and immunology.

• Monogenic vs. Polygenic: Monogenic traits are controlled by a single gene, while polygenic traits are influenced by multiple genes (e.g., skin color).

• Monohybrid vs. Dihybrid Cross: Monohybrid crosses involve one gene; dihybrid crosses involve two genes.

• Incomplete Dominance vs. Codominance: Incomplete dominance results in a blended phenotype (e.g., pink flowers from red and white parents), while codominance shows both alleles distinctly (e.g., AB blood type).

• DNA vs. RNA: DNA is double-stranded, contains deoxyribose, and uses thymine; RNA is single-stranded, contains ribose, and uses uracil.

• Replication vs. Transcription: Replication copies DNA; transcription synthesizes RNA from a DNA template.

• mRNA, rRNA, tRNA: mRNA carries genetic code; rRNA forms ribosomes; tRNA brings amino acids during translation.

• B Lymphocyte vs. T Lymphocyte: B cells produce antibodies (humoral immunity); T cells mediate cellular immunity.

• Helper T Cell vs. Cytotoxic T Cell: Helper T cells activate other immune cells; cytotoxic T cells destroy infected cells.

Processes in Genetics, Protein Synthesis, and Immunology

Several key biological processes underlie inheritance, protein production, and immune responses.

• Inheritance Using Punnett Squares: A grid system to predict offspring genotypes and phenotypes from parental crosses.

• Probability Ratios in Inheritance: The likelihood of inheriting specific traits, often expressed as ratios (e.g., 3:1).

• Test Cross: Crossing an individual with a dominant phenotype with a homozygous recessive to determine genotype.

• Pedigrees: Family trees used to track inheritance patterns of traits.

• Translation: The process where ribosomes synthesize proteins using mRNA as a template.

• Point and Frameshift Mutations: Point mutations change a single nucleotide; frameshift mutations add or remove nucleotides, altering the reading frame.

• Gene Therapy: The introduction or alteration of genes within an individual's cells to treat disease.

• Recombinant DNA and Cloning: Techniques for combining DNA from different sources and producing identical organisms or cells.

• Non-Specific Defense: General immune responses (e.g., skin, inflammation) that do not target specific pathogens.

• Humoral Immunity: Immunity mediated by antibodies produced by B cells.

• Cell-Mediated Immunity: Immunity involving T cells that attack infected or abnormal cells.

• Clonal Selection: The process by which an antigen selectively binds to and activates specific lymphocytes.

• HIV Infection: Human Immunodeficiency Virus attacks helper T cells, weakening the immune system.

Punnett Square: Dihybrid Cross Example

Predicting the outcome of a dihybrid cross (RrTt × RRTT) for petal color and plant height.

• Alleles: R = red petals, r = white petals; T = tall, t = short.

• Parent Genotypes: RrTt (heterozygous for both traits) × RRTT (homozygous dominant for both traits).

	RT	RT	Rt	Rt
RT	RRTT	RRTT	RRTt	RRTt
Rt	RRTt	RRTt	RRtt	RRtt
rT	RrTT	RrTT	RrTt	RrTt
rt	RrTt	RrTt	Rrtt	Rrtt

• Phenotype Ratios: All offspring will have red petals (at least one R) and most will be tall (at least one T). Only those with 'tt' will be short, but since the second parent is TT, no 'tt' offspring will occur. Thus, all are tall with red petals.

• Possible Genotypes: RRTT, RRTt, RRtt, RrTT, RrTt, Rrtt (but RRtt and Rrtt are not possible here since the second parent is TT).

Example: Crossing RrTt × RRTT yields only red, tall plants.

Transcription and Translation Example

Given a DNA template, determine the mRNA codon, tRNA anticodon, and the corresponding amino acid.

• DNA Template: TCG

• mRNA Codon: AGC (complementary to DNA template, replacing T with U in RNA)

• tRNA Anticodon: UCG (complementary to mRNA codon)

• Amino Acid: Serine (AGC codes for serine)

Mutation Example: If the DNA template changes from TCG to ACG:

• New mRNA Codon: UGC

• New Amino Acid: Cysteine (UGC codes for cysteine)

• Type of Mutation: Point mutation (single nucleotide change)

Additional info:

• For the dihybrid cross, since the second parent is homozygous dominant (RRTT), all offspring will inherit at least one dominant allele for each trait, so all will display the dominant phenotype (red, tall).

• Codon tables are used to determine which amino acid corresponds to a given mRNA codon.

• Point mutations can be silent, missense, or nonsense, depending on their effect on the amino acid sequence.