Cell Division, Inheritance, and Gene Expression: Study Guide

Chapter 12: The Cell Cycle and Mitosis

Why Organisms Undergo Mitosis vs. Meiosis

• Mitosis is the process by which somatic (body) cells divide to produce two genetically identical daughter cells. It is essential for growth, tissue repair, and asexual reproduction.

• Meiosis is the process by which gametes (sperm and egg cells) are produced. It reduces the chromosome number by half, resulting in genetic diversity among offspring.

Sister Chromatids and Homologous Chromosomes

• Sister chromatids are two identical copies of a single replicated chromosome, connected by a centromere. They are genetically identical (barring mutations).

• Homologous chromosomes are pairs of chromosomes (one from each parent) that have the same genes at the same loci but may have different alleles. They are not genetically identical.

End Products of Mitosis in Humans

• Produces two daughter cells.

• Each daughter cell is diploid (2n), containing the same number of chromosomes as the original cell (46 in humans).

• Daughter cells are genetically identical to each other and to the parent cell.

Chapter 13: Meiosis and Sexual Life Cycles

Gametes vs. Somatic Cells

• Gametes are reproductive cells (sperm and eggs) and are haploid (n), containing one set of chromosomes (23 in humans).

• Somatic cells are all other body cells and are diploid (2n), containing two sets of chromosomes (46 in humans).

• If given the chromosome number of one, you can determine the other: somatic cells have twice as many chromosomes as gametes.

Separation of Chromosomes During Meiosis and Mitosis

• In meiosis I, homologous chromosomes separate.

• In meiosis II, sister chromatids separate (similar to mitosis).

• In mitosis, only sister chromatids separate.

Genetic Variation: Crossing Over and Independent Assortment

• Crossing over is the exchange of genetic material between homologous chromosomes during prophase I of meiosis, increasing genetic diversity.

• Independent assortment refers to the random orientation of homologous chromosome pairs during metaphase I, leading to varied combinations of chromosomes in gametes.

End Products of Meiosis in Humans (Sperm)

• Produces four daughter cells.

• Each daughter cell is haploid (n), with 23 chromosomes.

• Daughter cells are genetically unique due to crossing over and independent assortment.

Chapter 14/15: Mendelian Genetics and Chromosomal Inheritance

Dominant and Recessive Traits

• Dominant alleles mask the effect of recessive alleles and are represented by uppercase letters (e.g., A).

• Recessive alleles are only expressed when two copies are present and are represented by lowercase letters (e.g., a).

Genotype and Phenotype

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

• Phenotype: The observable traits or characteristics (e.g., tall or short).

Homozygous and Heterozygous

• Homozygous dominant: Two dominant alleles (AA).

• Heterozygous: One dominant and one recessive allele (Aa).

• Homozygous recessive: Two recessive alleles (aa).

Monohybrid Crosses and Probability of Inheritance

• Monohybrid cross: A genetic cross involving one gene with two alleles.

• Autosomal dominant disease: Only one dominant allele needed for the trait to be expressed.

• Autosomal recessive disease: Two recessive alleles needed for the trait to be expressed.

Example Punnett Square for Autosomal Recessive Disease (Aa x Aa):

	A	a
A	AA	Aa
a	Aa	aa

• Probability of affected offspring (aa): 1/4

• Probability of carrier offspring (Aa): 1/2

• Probability of unaffected, non-carrier (AA): 1/4

Blood Types and Inheritance

• Blood types are determined by multiple alleles (A, B, O) and can be codominant (A and B).

• Possible genotypes: AA, AO, BB, BO, AB, OO.

• Offspring blood types depend on parental genotypes.

Pedigree Analysis

• Autosomal dominant: Trait appears in every generation; affected individuals have at least one affected parent.

• Autosomal recessive: Trait can skip generations; affected individuals may have unaffected parents.

• X-linked recessive: More common in males; affected males often have carrier mothers.

Chapter 16: The Molecular Basis of Inheritance

Semi-Conservative DNA Replication

• Each new DNA molecule consists of one original (parental) strand and one newly synthesized strand.

• This ensures genetic continuity between generations of cells.

Recognizing Complementary DNA Sequences

• Base pairing rules: A pairs with T, C pairs with G.

• Given a sequence, the complementary strand can be written using these rules.

Purpose of DNA Replication

• To accurately copy the genetic material before cell division, ensuring each daughter cell receives a complete genome.

Chapter 17: Gene Expression: From Gene to Protein

Genes and Genome

• Gene: A segment of DNA that codes for a functional product (usually a protein).

• Genome: The complete set of genetic material in an organism.

Order of Steps in Gene Expression

• 1. Transcription: DNA is used as a template to synthesize messenger RNA (mRNA).

• 2. Translation: mRNA is decoded by ribosomes to build a protein.

Redundancy in Codons

• Multiple codons can code for the same amino acid; this is called redundancy or degeneracy of the genetic code.

Transcription: Process Overview

• Starting product: DNA template strand.

• Ending product: mRNA molecule.

• Main components: RNA polymerase, promoter region, nucleotides (A, U, C, G).

Translation: Process Overview

• Starting product: mRNA molecule.

• Ending product: Polypeptide (protein).

• Main components: Ribosome, tRNA, amino acids, mRNA.

Mutations and Their Impact on Proteins

• A mutation in DNA can change the mRNA sequence, which may alter the amino acid sequence of the resulting protein.

• Types of mutations include silent, missense, and nonsense mutations.

• To determine the impact, transcribe the DNA to mRNA and use a codon dictionary to translate to amino acids.

Example: If DNA sequence changes from ATG to ATA:

• Original mRNA: UAC (codes for Tyrosine)

• Mutated mRNA: UAU (also codes for Tyrosine; silent mutation)

• If the change results in a different amino acid, it is a missense mutation; if it creates a stop codon, it is a nonsense mutation.

Additional info: Understanding these processes is fundamental for topics such as genetic engineering, disease inheritance, and biotechnology applications.