Exam 3 Study Guide: Macromolecules, Meiosis, Mendelian Genetics, and Chromosomal Inheritance

Macromolecules and Their Biological Roles

Polymers and Monomers

Macromolecules are large biological molecules essential for life, including carbohydrates, proteins, nucleic acids, and lipids. Most are polymers, long chains made from repeating units called monomers.

• Polymer: A long molecule consisting of many similar or identical building blocks (monomers) linked by covalent bonds.

• Monomer: The subunit that serves as the building block of a polymer.

• Dehydration synthesis: A chemical reaction in which two monomers are covalently bonded to each other with the removal of a water molecule.

• Hydrolysis: A reaction that breaks bonds between two molecules by the addition of water; functions in disassembly of polymers to monomers.

• Enzyme: A macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction without being consumed.

Carbohydrates

Carbohydrates are sugars and polymers of sugars, serving as fuel and building material.

• Monosaccharide: The simplest carbohydrate, active alone or serving as a monomer for disaccharides and polysaccharides (e.g., glucose).

• Disaccharide: A double sugar, consisting of two monosaccharides joined by a glycosidic linkage (e.g., maltose).

• Glycosidic linkage: A covalent bond formed between two monosaccharides by a dehydration reaction.

• Polysaccharide: A polymer of many monosaccharides, formed by dehydration reactions (e.g., starch, glycogen, cellulose).

• Starch: A storage polysaccharide in plants.

• Glycogen: A storage polysaccharide in animals.

• Cellulose: A structural polysaccharide in plant cell walls.

Lipids

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids.

• Fat: Constructed from glycerol and fatty acids; used for energy storage.

• Fatty acid: A carboxylic acid with a long carbon chain; can be saturated (no double bonds) or unsaturated (one or more double bonds).

• Phospholipid: A lipid with a phosphate group, major component of cell membranes.

• Steroid: Lipids with a carbon skeleton consisting of four fused rings (e.g., cholesterol).

• Cholesterol: A steroid that forms an essential component of animal cell membranes.

Proteins

Proteins are polymers of amino acids and perform a vast array of functions in the cell.

• Amino acid: Organic molecule with an amino group, carboxyl group, and side chain (R group).

• Polypeptide: A polymer of amino acids linked by peptide bonds.

• Protein: One or more polypeptides folded into a specific 3D structure.

• Peptide bond: Covalent bond between amino acids.

• Catalyst: Substance that speeds up a chemical reaction without being consumed.

• Protein structure: Four levels—primary (sequence), secondary (alpha helix/beta sheet), tertiary (3D folding), quaternary (multiple polypeptides).

• Denaturation: Loss of protein structure due to environmental changes.

Nucleic Acids

Nucleic acids store and transmit hereditary information.

• Nucleic acid: Polymer of nucleotides (DNA and RNA).

• Polynucleotide: Long chain of nucleotides.

• Ribose: Sugar in RNA.

• Deoxyribose: Sugar in DNA.

• Double helix: Structure of DNA, two strands coiled around each other.

Meiosis and Sexual Life Cycles

Basic Concepts

Meiosis is the process that produces gametes (sperm and egg cells) with half the chromosome number of somatic cells, enabling sexual reproduction.

• Gene: Unit of hereditary information on a chromosome.

• Gamete: Reproductive cell (sperm or egg).

• Somatic cell: Any cell other than a gamete.

• Locus: Specific location of a gene on a chromosome.

• Asexual reproduction: Offspring arise from a single organism, genetically identical to the parent.

• Clone: Genetically identical individual from a single parent.

• Sexual reproduction: Offspring inherit genes from two parents.

Chromosomes and Meiosis

• Karyotype: Ordered display of chromosome pairs.

• Homologous chromosomes: Chromosome pairs with genes for the same traits.

• Sex chromosome: Chromosomes that determine sex (X and Y).

• Autosome: Non-sex chromosomes.

• Diploid (2n): Two sets of chromosomes.

• Haploid (n): One set of chromosomes.

• Fertilization: Fusion of gametes to form a zygote.

• Meiosis: Two-stage cell division producing haploid gametes.

Phases of Meiosis

• Meiosis I: Homologous chromosomes separate, reducing chromosome number by half.

• Meiosis II: Sister chromatids separate.

• Crossing over: Exchange of genetic material between homologous chromosomes, increasing genetic diversity.

Genetic Variation

• Independent assortment: Random distribution of homologous chromosomes during meiosis I.

• Recombinant chromosome: Chromosome with a mix of maternal and paternal genes due to crossing over.

• Random fertilization: Any sperm can fertilize any egg, increasing genetic variation.

Mendelian Genetics and Inheritance Patterns

Basic Principles

Mendelian genetics explains how traits are inherited through generations using laws of segregation and independent assortment.

• Character: Heritable feature (e.g., flower color).

• Trait: Variant of a character (e.g., purple or white flowers).

• True-breeding: Organisms that produce offspring of the same variety when self-pollinated.

• P generation: Parental generation.

• F1 generation: First filial generation, offspring of P generation.

• F2 generation: Second filial generation, offspring of F1.

• Law of segregation: Two alleles for a gene separate during gamete formation.

• Allele: Alternative versions of a gene.

• Dominant allele: Expressed in the phenotype.

• Recessive allele: Masked in the presence of a dominant allele.

• Punnett Square: Diagram to predict genotype and phenotype ratios.

• Homozygous: Two identical alleles for a gene.

• Heterozygous: Two different alleles for a gene.

• Phenotype: Observable traits.

• Genotype: Genetic makeup.

• Test cross: Breeding with a homozygous recessive to determine genotype.

• Monohybrid cross: Cross involving one character.

• Dihybrid cross: Cross involving two characters.

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

Non-Mendelian Inheritance

• Complete dominance: Phenotype of heterozygote is identical to dominant homozygote.

• Incomplete dominance: Heterozygote phenotype is intermediate between homozygotes.

• Codominance: Both alleles are fully expressed in heterozygotes.

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

• Polygenic inheritance: Multiple genes affect a single trait.

Pedigrees and Human Genetics

• Pedigree: Family tree showing inheritance of traits.

• Carrier: Heterozygote for a recessive disorder.

• Multifactorial disorder: Influenced by genetic and environmental factors.

Chromosomal Basis of Inheritance

Chromosome Theory and Sex-Linked Genes

The chromosome theory of inheritance states that genes are located on chromosomes, which segregate and independently assort during meiosis.

• Homologous chromosome: Pair of chromosomes with the same genes.

• Sister chromatid: Identical copies of a chromosome connected by a centromere.

• Gamete: Reproductive cell.

• Sex-linked gene: Gene located on a sex chromosome.

• X-linked gene: Gene located on the X chromosome.

Chromosomal Alterations

• Nondisjunction: Failure of chromosomes to separate properly during meiosis.

• Aneuploidy: Abnormal number of chromosomes.

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

• Trisomic: Extra chromosome (2n+1).

• Polyploidy: More than two complete sets of chromosomes.

• Deletion: Loss of a chromosome segment.

• Duplication: Repetition of a chromosome segment.

• Inversion: Reversal of a chromosome segment.

• Translocation: Movement of a segment from one chromosome to another.

Short Answer Practice and Example Problems

1. Dehydration Reaction and Maltose Formation

When two glucose molecules (C6H12O6) join via dehydration synthesis, a water molecule (H2O) is lost. Thus, the formula for maltose is:

• Formula: C12H22O11

• Reason: The loss of one H2O (2H and 1O) during bond formation.

2. Gene Expression and Inheritance of Traits

Traits are inherited because offspring receive genes from their parents. Genes encode proteins, which determine traits (e.g., hair color). During reproduction, alleles are passed from parents to offspring, and gene expression leads to the development of observable characteristics.

3. Offspring Genotype Proportions from AA x Aa Cross

• AA (homozygous dominant): 50%

• Aa (heterozygous): 50%

• aa (homozygous recessive): 0%

4. Red-Eyed Female x White-Eyed Male Drosophila Cross

Red eyes are dominant (XR), white eyes are recessive (Xr). The cross is XRXR (female) x XrY (male).

• Offspring genotypes: XRXr (female), XRY (male)

• Offspring phenotypes: All females red-eyed, all males red-eyed

• Why more probable for males to be white-eyed? Males have only one X chromosome; if they inherit Xr, they express the trait because there is no second X to mask it.

Table: Types of Inheritance Patterns

Pattern	Description	Example
Complete Dominance	Heterozygote phenotype same as dominant homozygote	Purple flower color in peas
Incomplete Dominance	Heterozygote phenotype intermediate	Pink snapdragon flowers
Codominance	Both alleles fully expressed	AB blood type
X-Linked	Gene located on X chromosome	Red/white eye color in Drosophila