BIO 101 Chapters 8-10 Study Guide: Cellular Reproduction, Patterns of Inheritance, and Molecular Biology of the Gene

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Cellular Reproduction

Role of Mitosis in Organisms

Mitosis is a fundamental process for growth, development, tissue repair, and asexual reproduction in multicellular organisms.

Growth and Development: Mitosis increases cell number, allowing organisms to grow.
Tissue Repair: Damaged tissues are replaced by new cells produced via mitosis.
Asexual Reproduction: Some organisms reproduce by mitosis, producing genetically identical offspring.

Sexual vs. Asexual Reproduction

Organisms reproduce either sexually or asexually, each with distinct genetic outcomes.

Asexual Reproduction: Offspring are genetically identical to the parent (clones).
Sexual Reproduction: Involves fusion of gametes, resulting in genetically diverse offspring.
Example: Bacteria reproduce asexually by binary fission; humans reproduce sexually.
Binary fission- cell division by halving ( utilized by prokaryotic and some unicellular prokaryotic( ex amoeba , Paramecium)
budding : cell division by producing a bud ( fungi, yeast and sponges)

Chromosome Structure and Terminology

Chromosomes are structures that carry genetic information. Key terms include:

Centromere: Region where sister chromatids are joined.
Chromatid: Each half of a duplicated chromosome.
Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.
Sister Chromatids: Identical copies formed during DNA replication.

Cell Cycle Phases

The cell cycle consists of interphase (G1, S, G2) and mitotic phase (mitosis and cytokinesis).

G1 Phase: Cell growth.
S Phase: DNA replication.
G2 Phase: Preparation for mitosis.
Mitosis: Division of the nucleus.
Cytokinesis: Division of the cytoplasm.

Mitosis Stages

Mitosis is divided into five stages:

Prophase: Chromosomes condense, spindle forms.
Prometaphase: Nuclear envelope breaks down, spindle attaches to chromosomes.
Metaphase: Chromosomes align at the cell equator.
Anaphase: Sister chromatids separate and move to opposite poles.
Telophase: Nuclear envelopes reform, chromosomes decondense.
3 forces that act to pull chromosomes apart in anaphase: the kinetochore for each daughter chromosome “walks” the chromosome along the mitotic spindle towards its centrosome. ◦ The spindles attached to the daughter chromosomes shorten to pull chromosomes toward opposite pole. ◦ The spindles attached to those spindles from the opposite pole elongate, pushing the poles farther apart. Walk toward centrosome Shorten spindle Elongate attached spindles pushing centrosomes apart

Cytokinesis

Cytokinesis divides the cytoplasm, resulting in two daughter cells.

Animal Cells: Cleavage furrow forms.
Plant Cells: Cell plate forms.

Control of the Cell Cycle

Cell cycle progression is regulated by checkpoints and specific proteins (cyclins and CDKs).

Checkpoints: Ensure proper DNA replication and division.
Disruption: Can lead to uncontrolled cell division (cancer).

Meiosis Overview

Meiosis is a specialized cell division that produces gametes (sperm and egg) with half the chromosome number.

Meiosis I: Homologous chromosomes separate.
Meiosis II: Sister chromatids separate.
Result: Four genetically unique haploid cells.

Genetic Variation in Meiosis

Meiosis introduces genetic diversity through:

Synapsis and Crossing Over: Homologous chromosomes exchange genetic material.
Independent Assortment: Random orientation of homologous pairs at metaphase I.

Chromosome Segregation and Errors

Errors in chromosome segregation can lead to aneuploidy (abnormal chromosome number).

Nondisjunction: Failure of chromosomes to separate properly.
Example: Down syndrome (trisomy 21).

Patterns of Inheritance

Mendelian Genetics

Gregor Mendel discovered fundamental laws of inheritance using pea plants.

Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.
Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

Monohybrid and Dihybrid Crosses

Genetic crosses predict offspring genotypes and phenotypes.

Monohybrid Cross: Involves one gene; typical ratio is 3:1 (dominant:recessive).
Dihybrid Cross: Involves two genes; typical ratio is 9:3:3:1.
Example: Crossing pea plants for seed color and shape.

Probability in Genetics

Probability is used to predict genetic outcomes.

Phenotypic Ratio: Ratio of observable traits.
Genotypic Ratio: Ratio of genetic makeup.
Formula:

Genetic Terminology

Allele: Alternative form of a gene.
Homozygous: Two identical alleles.
Heterozygous: Two different alleles.
Dominant: Expressed trait.
Recessive: Masked trait.

Pedigree Analysis

Pedigrees trace inheritance patterns in families.

Symbols: Squares (males), circles (females), shaded (affected).
Application: Used to identify carriers and predict genetic disorders.

Non-Mendelian Inheritance

Some traits do not follow Mendel's laws.

Incomplete Dominance: Heterozygotes show intermediate phenotype.
Codominance: Both alleles are expressed equally.
Polygenic Inheritance: Multiple genes influence a trait.

Sex-Linked and Autosomal Inheritance

Genes located on sex chromosomes show unique inheritance patterns.

Sex-Linked: Traits carried on X or Y chromosomes.
Autosomal: Traits carried on non-sex chromosomes.
Example: Color blindness (X-linked recessive).

Molecular Biology of the Gene

DNA Structure

DNA is a double helix composed of nucleotides.

Nucleotide: Consists of a phosphate group, deoxyribose sugar, and nitrogenous base.
Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
Base Pairing: A pairs with T, C pairs with G.
Double Helix: Two strands run antiparallel and are held together by hydrogen bonds.

DNA Replication

DNA replication is semi-conservative, producing two identical DNA molecules.

Process: Each strand serves as a template for a new strand.
Enzymes: DNA polymerase synthesizes new DNA.
Replication Fork: Site where DNA unwinds and replication occurs.

Central Dogma: Transcription and Translation

Genetic information flows from DNA to RNA to protein.

Transcription: DNA is transcribed into messenger RNA (mRNA).
Translation: mRNA is translated into a protein at the ribosome.
Codon: Three-nucleotide sequence on mRNA that codes for an amino acid.
Example: codes for methionine (start codon).

Genetic Code

The genetic code is universal and redundant.

64 Codons: Specify 20 amino acids and stop signals.
Redundancy: Multiple codons can code for the same amino acid.

Mutations

Mutations are changes in DNA sequence that can affect protein function.

Types: Point mutations, insertions, deletions.
Effects: Can be silent, missense, or nonsense.
Example: Sickle cell anemia is caused by a point mutation in the hemoglobin gene.

Gene Regulation

Gene expression is controlled at multiple levels.

Promoters and Enhancers: DNA sequences that regulate transcription.
Epigenetics: Modifications that affect gene expression without changing DNA sequence.

Protein Synthesis

Proteins are synthesized by ribosomes using mRNA as a template.

tRNA: Transfers amino acids to the ribosome.
rRNA: Forms the core of the ribosome's structure.
Process: Initiation, elongation, termination.

Summary Table: Key Differences Between Mitosis and Meiosis

Feature	Mitosis	Meiosis
Number of Divisions	1	2
Number of Daughter Cells	2	4
Genetic Identity	Identical	Unique
Chromosome Number	Diploid	Haploid
Function	Growth, repair, asexual reproduction	Sexual reproduction