Genetics, Molecular Biology, and Evolution: Study Guide for BIOL 114 Exam 4

Genetics and Heredity

Heredity vs. Genetics vs. Genes

Heredity is the passing of traits from parents to offspring, while genetics is the scientific study of heredity and variation. Genes are specific sequences of DNA that code for proteins and determine traits.

• Heredity: Transmission of genetic information from one generation to the next.

• Genetics: The study of genes, genetic variation, and heredity in living organisms.

• Gene: A segment of DNA that encodes a functional product, usually a protein.

• Example: Eye color inheritance in humans is determined by multiple genes.

Chromosomes and Chromosome Types

• Homologous Chromosomes: Chromosome pairs, one from each parent, that are similar in length, gene position, and centromere location.

• Karyotype: The number and appearance of chromosomes in the nucleus of a eukaryotic cell.

• Sex Chromosomes vs. Autosomes: Sex chromosomes determine the sex of an organism (e.g., X and Y in humans), while autosomes are all other chromosomes.

Sexual vs. Asexual Reproduction

• Asexual Reproduction: Offspring arise from a single organism, inheriting the genes of that parent only.

• Sexual Reproduction: Involves the combination of genetic material from two parents, increasing genetic diversity.

Meiosis and Mitosis

• Meiosis: A type of cell division that reduces the chromosome number by half, producing four haploid cells (gametes).

• Mitosis: Cell division resulting in two genetically identical diploid cells.

• Stages of Meiosis: Includes two rounds of division: Meiosis I (homologous chromosomes separate) and Meiosis II (sister chromatids separate).

• Crossing Over: Exchange of genetic material between homologous chromosomes during Prophase I of meiosis, increasing genetic variation.

Mendelian Genetics

Principles of Inheritance

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

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

• Monohybrid Cross: A cross between individuals heterozygous for a single trait.

• Dihybrid Cross: A cross between individuals heterozygous for two traits.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable physical or physiological traits of an organism.

• Homozygous: Having two identical alleles for a gene.

• Heterozygous: Having two different alleles for a gene.

Non-Mendelian Inheritance

• Incomplete Dominance: Heterozygote has an intermediate phenotype.

• Codominance: Both alleles are fully expressed in the phenotype.

• Pleiotropy: One gene influences multiple phenotypic traits.

• Epistasis: One gene affects the expression of another gene.

• Polygenic Inheritance: Multiple genes influence a single trait.

Sex-Linked Inheritance

• X-linked Genes: Genes located on the X chromosome; often show different inheritance patterns in males and females.

• Example: Color blindness is an X-linked recessive trait.

DNA Structure and Replication

DNA Structure

• Double Helix: DNA consists of two antiparallel strands forming a double helix.

• Nucleotides: Each nucleotide contains a phosphate group, deoxyribose sugar, and a nitrogenous base (A, T, C, G).

• Base Pairing: Adenine pairs with Thymine, Cytosine pairs with Guanine.

• Watson and Crick: Discovered the double helix structure of DNA.

DNA Replication

• Semiconservative Replication: Each new DNA molecule consists of one old strand and one new strand.

• Enzymes Involved: DNA polymerase (synthesizes new DNA), helicase (unwinds DNA), primase (synthesizes RNA primer), ligase (joins Okazaki fragments).

• Leading vs. Lagging Strand: Leading strand is synthesized continuously; lagging strand is synthesized in short fragments (Okazaki fragments).

• Antiparallel Elongation: DNA strands run in opposite directions (5' to 3' and 3' to 5').

DNA Repair and Proofreading

• Proofreading: DNA polymerase checks and corrects errors during replication.

• DNA Repair Mechanisms: Include mismatch repair, excision repair, and direct repair.

Gene Expression and Regulation

Central Dogma of Molecular Biology

• Central Dogma: Information flows from DNA to RNA to protein.

• Transcription: Synthesis of RNA from a DNA template.

• Translation: Synthesis of protein from an mRNA template.

Transcription

• Enzymes: RNA polymerase synthesizes RNA.

• Promoter: DNA sequence where RNA polymerase binds to initiate transcription.

• mRNA Processing: Includes addition of 5' cap, poly-A tail, and splicing of introns.

Translation

• Ribosome: Site of protein synthesis; composed of rRNA and proteins.

• tRNA: Transfers amino acids to the ribosome during protein synthesis.

• Codons: Three-nucleotide sequences in mRNA that specify amino acids.

Gene Regulation

• Prokaryotic Regulation: Operons (e.g., lac operon) control gene expression.

• Eukaryotic Regulation: Involves enhancers, silencers, transcription factors, and epigenetic modifications.

Chromosome Structure and Function

Chromatin Organization

• Chromatin: DNA-protein complex that packages DNA in the nucleus.

• Heterochromatin: Densely packed, transcriptionally inactive chromatin.

• Euchromatin: Loosely packed, transcriptionally active chromatin.

Telomeres and Centromeres

• Telomeres: Repetitive DNA sequences at chromosome ends, protecting them from degradation.

• Centromere: Region where sister chromatids are joined and spindle fibers attach during cell division.

Mutation and DNA Technology

Types of Mutations

• Point Mutation: Change in a single nucleotide.

• Frameshift Mutation: Insertion or deletion of nucleotides that alters the reading frame.

• Chromosomal Mutations: Include deletions, duplications, inversions, and translocations.

DNA Technology

• Restriction Enzymes: Cut DNA at specific sequences.

• Transformation: Uptake of foreign DNA by a cell.

• Gel Electrophoresis: Technique to separate DNA fragments by size.

Population Genetics and Evolution

Hardy-Weinberg Principle

• Definition: Describes a non-evolving population where allele and genotype frequencies remain constant.

• Equation: $p^2 + 2pq + q^2 = 1$ where $p$ and $q$ are the frequencies of two alleles.

Mechanisms of Evolution

• Natural Selection: Differential survival and reproduction of individuals due to differences in phenotype.

• Genetic Drift: Random changes in allele frequencies, especially in small populations.

• Gene Flow: Movement of alleles between populations.

• Bottleneck Effect: Sharp reduction in population size, reducing genetic diversity.

• Founder Effect: New population established by a small number of individuals, leading to reduced genetic variation.

Speciation

• Definition: Formation of new and distinct species in the course of evolution.

• Reproductive Isolation: Mechanisms that prevent species from interbreeding.

Laboratory Concepts

Transformation and Restriction Digests

• Transformation: Introduction of foreign DNA into a bacterial cell.

• Restriction Digest: Use of restriction enzymes to cut DNA at specific sites for analysis.

Polytene Chromosomes

• Definition: Giant chromosomes found in certain tissues of insects, useful for studying gene expression and chromosomal structure.

Molecular Evolution

• Definition: Study of evolutionary changes at the molecular level, such as DNA, RNA, and proteins.

Summary Table: Key Genetic Terms

Term	Definition	Example
Gene	Segment of DNA coding for a protein	Gene for eye color
Allele	Different forms of a gene	A and a alleles for flower color
Genotype	Genetic makeup	AA, Aa, aa
Phenotype	Physical expression	Purple or white flowers
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Allele expressed in heterozygote	A in Aa
Recessive	Allele masked in heterozygote	a in Aa

Additional info: Some explanations and examples have been expanded for clarity and completeness, and to ensure the notes are self-contained for exam preparation.