Genetics and Molecular Biology: Key Concepts for Final Exam

Genetics and Molecular Biology: Key Concepts for Final Exam

Chapter 14: Mendelian Genetics

This chapter covers the foundational principles of inheritance as discovered by Gregor Mendel, focusing on how traits are transmitted from parents to offspring.

• Genotype: The genetic makeup of an organism; the combination of alleles present at specific loci.

• Phenotype: The observable physical or physiological traits of an organism, determined by its genotype and environment.

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation so that each gamete carries only one allele for each gene.

• Law of Independent Assortment: Genes for different traits can segregate independently during the formation of gametes.

• Monohybrid Cross: A genetic cross involving a single trait, typically between individuals heterozygous for that trait (e.g., Aa x Aa).

• Dihybrid Cross: A cross between individuals heterozygous for two traits (e.g., AaBb x AaBb), demonstrating independent assortment.

• Complete Dominance: The dominant allele completely masks the effect of the recessive allele in heterozygotes.

• Incomplete Dominance: The phenotype of heterozygotes is intermediate between those of the two homozygotes (e.g., red x white flowers produce pink offspring).

• Carrier: An individual who is heterozygous for a recessive trait and can pass the allele to offspring without showing the phenotype.

Example: In a monohybrid cross of pea plants (Pp x Pp), the genotypic ratio is 1:2:1 (PP:Pp:pp), and the phenotypic ratio is 3:1 (dominant:recessive).

Chapter 15: Chromosomal Basis of Inheritance

This chapter explores how chromosomes carry genetic information and how their behavior during meiosis explains Mendelian inheritance patterns.

• Chromosome Theory of Inheritance: Genes are located on chromosomes, and the behavior of chromosomes during meiosis accounts for inheritance patterns.

• Wild Type: The most common phenotype or allele in a natural population.

• Inheritance of X-linked Genes: Genes located on the X chromosome exhibit unique inheritance patterns, often affecting males more than females (e.g., color blindness).

• Nondisjunction: Failure of homologous chromosomes or sister chromatids to separate properly during meiosis, leading to abnormal chromosome numbers in gametes.

• Aneuploidy: Abnormal number of chromosomes (not a complete set). Types include:

  • Monosomic: Missing one chromosome (2n-1).

  • Trisomic: Having an extra chromosome (2n+1).

  • Polyploidy: More than two complete sets of chromosomes (common in plants).

• Alteration of Chromosome Structure: Structural changes include deletion, duplication, inversion, and translocation (see Figure 15.14 in textbooks).

Example: Down syndrome is caused by trisomy 21 (an extra copy of chromosome 21).

Chapter 16: The Molecular Basis of Inheritance

This chapter focuses on the structure of DNA and the mechanisms by which it is replicated in cells.

• DNA Structure: DNA is a double helix composed of two antiparallel strands of nucleotides, with complementary base pairing (A-T, G-C).

• Process of DNA Replication: DNA replication is semiconservative, meaning each new DNA molecule consists of one old strand and one new strand.

• Semiconservative Model: Each daughter DNA molecule contains one parental strand and one newly synthesized strand.

• Telomeres: Repetitive nucleotide sequences at the ends of eukaryotic chromosomes that protect genes from erosion during replication.

Example: DNA polymerase synthesizes new DNA in the 5' to 3' direction, using the parental strand as a template.

Key Equation:

• $\text{DNA}_{\text{parent}} \rightarrow \text{DNA}_{\text{daughter}} = (\text{old strand}) + (\text{new strand})$

Chapter 17: Gene Expression

This chapter explains how genetic information flows from DNA to RNA to protein, a process known as gene expression.

• Gene Expression: The process by which information from a gene is used to synthesize a functional gene product (usually a protein).

• Process of Transcription: Synthesis of RNA from a DNA template by RNA polymerase.

• Process of Translation: Synthesis of a polypeptide (protein) using the information encoded in mRNA, occurring at the ribosome.

Example: The central dogma of molecular biology: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Chapter 18: Regulation of Gene Expression

This chapter discusses how cells control the expression of their genes, allowing for specialization and adaptation.

• Operons: A cluster of functionally related genes under the control of a single promoter, common in prokaryotes.

• Inducible Operon vs. Repressible Operon:

  • Inducible Operon: Usually off but can be turned on by an inducer (e.g., lac operon).

  • Repressible Operon: Usually on but can be turned off by a corepressor (e.g., trp operon).

• Histone Acetylation: Addition of acetyl groups to histone proteins, loosening chromatin structure and promoting gene expression.

• DNA Methylation: Addition of methyl groups to DNA, often leading to gene silencing.

• Non-coding RNA: RNA molecules that are not translated into proteins but have regulatory roles (e.g., microRNA, siRNA).

Example: The lac operon in Escherichia coli is an inducible operon activated in the presence of lactose.

Chapters 17 & 23: Mutations

Mutations are changes in the genetic material that can affect gene function and phenotype.

• Mutations: Permanent changes in the DNA sequence.

• Point Mutation: A change in a single nucleotide pair in DNA.

• Silent Mutation: Alters a codon but does not change the amino acid sequence of the protein.

• Missense Mutation: Changes one amino acid in the protein sequence.

• Nonsense Mutation: Changes a codon to a stop codon, resulting in premature termination of translation.

• Frameshift Mutation: Insertion or deletion of nucleotides not in multiples of three, altering the reading frame of the gene.

Example: Sickle cell anemia is caused by a missense mutation in the beta-globin gene.

Table: Types of Mutations and Their Effects

Type of Mutation	Description	Effect on Protein
Silent	Change in nucleotide does not alter amino acid	No effect
Missense	Change in nucleotide alters one amino acid	May alter protein function
Nonsense	Change in nucleotide creates a stop codon	Premature termination; usually nonfunctional protein
Frameshift	Insertion/deletion shifts reading frame	Alters downstream amino acids; usually nonfunctional protein

Additional info: For more detailed mechanisms and examples, refer to the relevant textbook chapters and figures (e.g., Figure 15.14 for chromosome structure alterations).