Study Guide: Meiosis, Mendelian Genetics, Chromosomal Inheritance, and DNA Structure & Replication

CHAPTER 10 — MEIOSIS

Key Terminology

• Heredity: The transmission of traits from parents to offspring.

• Variation: Differences among individuals in a population.

• Genetics: The scientific study of heredity and variation.

• Genes: Units of heredity made up of DNA; code for proteins.

• Gametes: Reproductive cells (sperm and egg) with half the number of chromosomes.

• Somatic cells: All body cells except gametes; contain a full set of chromosomes.

• Homologous chromosomes: Chromosome pairs, one from each parent, with genes for the same traits.

Sexual vs. Asexual Reproduction

• Sexual reproduction: Involves fusion of gametes; offspring have genetic variation.

• Asexual reproduction: Offspring are genetically identical to the parent; no gamete fusion.

• Example: Bacteria reproduce asexually by binary fission; humans reproduce sexually.

Diploid (2n) vs. Haploid (n) Cells

• Diploid (2n): Cells with two sets of chromosomes (e.g., somatic cells).

• Haploid (n): Cells with one set of chromosomes (e.g., gametes).

• Example: Human somatic cells are diploid (46 chromosomes); gametes are haploid (23 chromosomes).

Human Sexual Life Cycle and the Role of Meiosis

• Meiosis reduces chromosome number by half, producing haploid gametes.

• Fertilization restores diploid number in the zygote.

• Meiosis ensures genetic diversity in offspring.

Events of Meiosis I and Meiosis II

• Meiosis I: Homologous chromosomes separate; crossing over occurs in Prophase I.

• Meiosis II: Sister chromatids separate; similar to mitosis.

• Stages: Prophase I, Metaphase I, Anaphase I, Telophase I; Prophase II, Metaphase II, Anaphase II, Telophase II.

Three Factors Contributing to Genetic Diversity

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

• Crossing over: Exchange of genetic material between homologous chromosomes in Prophase I.

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

CHAPTER 11 — MENDELIAN GENETICS

Why Mendel Used Pea Plants

• Pea plants have easily observable traits, short generation times, and can self- or cross-pollinate.

• Allowed Mendel to control breeding and study inheritance patterns.

Key Terms

• Dominant: Trait expressed when at least one dominant allele is present.

• Recessive: Trait expressed only when two recessive alleles are present.

• Alleles: Different versions of a gene.

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

• Phenotype: Observable traits (e.g., flower color).

Mendel’s P, F1, and F2 Generations

• P (parental) generation: True-breeding parents.

• F1 (first filial) generation: Offspring of P generation; all show dominant trait.

• F2 (second filial) generation: Offspring of F1; show both dominant and recessive traits.

Monohybrid Crosses and Predicting Ratios

• Cross between parents differing in one trait.

• Use Punnett squares to predict genotypic and phenotypic ratios.

• Example: Aa x Aa yields 1 AA : 2 Aa : 1 aa (genotype), 3 dominant : 1 recessive (phenotype).

Dihybrid Cross and the 9:3:3:1 Ratio

• Cross between parents differing in two traits.

• Phenotypic ratio in F2 generation is 9:3:3:1.

Mendel’s Four Concepts

• Genes exist in pairs (alleles).

• Alleles segregate during gamete formation (law of segregation).

• Dominant alleles mask recessive alleles.

• Alleles assort independently (law of independent assortment).

Law of Segregation

• Each gamete receives only one allele for each gene.

• Explains why offspring inherit one trait from each parent.

CHAPTER 12 — CHROMOSOMES & INHERITANCE

Terminology

• Wild-type: Most common phenotype in a population.

• Mutant: Phenotype resulting from a mutation.

• Sex-linked genes: Genes located on sex chromosomes (X or Y).

• Linked vs. unlinked genes: Linked genes are inherited together; unlinked genes assort independently.

• Hemizygous: Having only one allele for a gene (e.g., males for X-linked genes).

X-linked Punnett Squares and Trait Expression

• X-linked traits are often expressed in males because they have only one X chromosome.

• Females must inherit two copies of a recessive X-linked allele to express the trait.

• Example: Color blindness is more common in males.

Nondisjunction, Aneuploidy, and Polyploidy

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

• Aneuploidy: Abnormal number of chromosomes (e.g., trisomy 21 causes Down syndrome).

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

Alterations in Chromosome Structure

• Deletion: Loss of a chromosome segment.

• Duplication: Repetition of a chromosome segment.

• Inversion: Reversal of a segment within a chromosome.

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

CHAPTER 13 — DNA STRUCTURE & REPLICATION

DNA Structure and Function

• DNA is a double helix composed of two antiparallel strands.

• Stores genetic information for protein synthesis.

Nucleotide Components and Base Pairing

• Each nucleotide consists of a phosphate group, a deoxyribose sugar, and a nitrogenous base.

• Bases pair as follows: Adenine (A) with Thymine (T), Guanine (G) with Cytosine (C).

• Purines: A and G; Pyrimidines: C and T.

DNA vs RNA; 5' End vs 3' End

• DNA contains deoxyribose; RNA contains ribose.

• DNA uses thymine; RNA uses uracil.

• 5' end has a phosphate group; 3' end has a hydroxyl group.

DNA Replication Enzymes and Functions

• Helicase: Unwinds the DNA double helix.

• Primase: Synthesizes RNA primers.

• DNA polymerase: Adds nucleotides to the growing DNA strand.

• Ligase: Joins Okazaki fragments on the lagging strand.

Leading vs Lagging Strands; Okazaki Fragments

• Leading strand is synthesized continuously toward the replication fork.

• Lagging strand is synthesized discontinuously, forming Okazaki fragments.

Semiconservative DNA Replication

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

• Equation:

$\text{Parent DNA} \rightarrow \text{Daughter DNA:} \ \text{one old strand} + \text{one new strand}$

Practice DNA Replication Example

• Given template: 5’-ATTGCCGAT-3’

• Complementary strand: 3’-TAACGGCTA-5’

REVIEW CONCEPTS

Cell Types and Chromosome Number

• Somatic cells: diploid; gametes: haploid.

• Mitosis produces identical cells; meiosis produces genetically diverse gametes.

Genotype, Phenotype, and Alleles

• Genotype: AA, Aa, or aa.

• Phenotype: Physical expression (e.g., purple or white flowers).

• Alleles: Different forms of a gene.

• Homozygous dominant: AA; Heterozygous: Aa; Homozygous recessive: aa.

Meiosis Stages and Crossing Over

• Crossing over occurs in Prophase I.

• Homologous chromosomes pair and exchange genetic material.

Mendelian Laws

• Law of segregation: Alleles separate during gamete formation.

• Law of independent assortment: Genes on different chromosomes assort independently.

Punnett Squares and Types of Dominance

• Used to predict genotype and phenotype ratios.

• Complete dominance: One allele completely masks the other.

• Incomplete dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are fully expressed.

• X-linked genes: Traits determined by genes on the X chromosome.

Large-Scale Mutations

• Nondisjunction: Chromosomes fail to separate; results in aneuploidy.

• Chromosomal structure alterations: Translocation, deletion, duplication, inversion.

Nucleotide Structure and DNA Ends

• Nucleotide: phosphate, sugar, nitrogenous base.

• 3' end: hydroxyl group; 5' end: phosphate group.

DNA Replication Details

• Semiconservative: each new DNA has one old and one new strand.

• Begins at origins of replication.

• Enzymes: helicase, primase, DNA polymerase, ligase.

• Leading strand: continuous; lagging strand: Okazaki fragments.

• Antiparallel: strands run in opposite directions.

Summary Table: Types of Chromosomal Mutations

Type	Description	Example
Deletion	Loss of a chromosome segment	Cri du chat syndrome
Duplication	Repeat of a chromosome segment	Charcot-Marie-Tooth disease
Inversion	Reversal of a segment within a chromosome	Some hemophilia cases
Translocation	Segment moves to another chromosome	Chronic myelogenous leukemia

Summary Table: DNA Replication Enzymes

Enzyme	Function
Helicase	Unwinds DNA double helix
Primase	Synthesizes RNA primer
DNA Polymerase	Adds nucleotides to new DNA strand
Ligase	Joins Okazaki fragments

Additional info: Academic context and examples were added to clarify concepts and provide self-contained explanations for exam preparation.