gen bio outline 10 & 11

What are the three core principles of Cell Theory?

1. All cellular life is made of one or more cells.

2. Cells are the basic organizational and functional units.

3. All cells come from pre-existing cells.

What is the primary function of cell division?

To distribute genetic material into daughter cells.

Genome

A cell’s total genetic material

How does the genome structure differ between prokaryotes and eukaryotes?

• Prokaryotes: Usually 1 circular DNA molecule.

• Eukaryotes: Usually more than 1 linear DNA molecule.

Chromatin

A complex of DNA and proteins in a dispersed, loosely packed state; present when the cell is not actively dividing.

Chromosome (during cell division)

A highly condensed, densely packaged structure of DNA and proteins ("colored body") only visible during cell division.

Haploid (n)

Having one complete set of chromosomes (1 of each type); characteristic of gametes

Diploid (2n)

Having two complete sets of chromosomes (2 of each type, known as a homologous pair)

Homologous Chromosomes

A pair of chromosomes that share the same length, structural features, and the same genes.

What type of cells can undergo mitosis?

Both haploid and diploid cells can undergo mitosis.

How do prokaryotes reproduce?

Through binary fission, which is simpler than mitosis

Interphase

The highly active time between cell divisions (growth, synthesis, metabolism). It makes up at least 90% of the cell cycle

What state is DNA in during Interphase?

Chromatin (dispersed state)

G₁ Phase (Gap 1)

The phase dedicated to cell growth, development, and normal metabolic functions. Many cells spend most of their lives here

S Phase (Synthesis)

The phase where DNA replication occurs.

Does DNA replication in the S phase change the ploidy of the cell?

no

Sister Chromatids

Two identical copies of a replicated chromosome that are connected at the centromere

G₂ Phase (Gap 2)

The phase characterized by high metabolic activity and final preparations for mitosis. Usually the shortest part of interphase.

M Phase

The shorter part of the cell cycle (<10%) that includes both mitosis (nuclear division) and cytokinesis (cellular division).

Mitosis

The nuclear division of somatic cells, divided into 4 stages: Prophase, Metaphase, Anaphase, and Telophase (PMAT).

Prophase

1. Chromatin condenses into visible chromosomes.

2. The nucleus breaks down.

3. The mitotic spindle forms.

Mitotic Spindle

A network of spindle fibers oriented pole-to-pole that guides chromosome movement during mitosis.

Metaphase

Chromosomes align along the center of the cell at the metaphase plate (a location, not a physical structure).

Anaphase

Sister chromatids separate and move toward opposite poles, pulled by kinetochores attached to their centromeres.

When is a chromatid officially considered an individual chromosome?

Immediately after sister chromatids separate during anaphase.

Telophase

The opposite of prophase: Chromosomes de-condense back into chromatin, and the nuclear envelope reforms to create two identical nuclei.

Cytokinesis

The division of the cytoplasm/cell into two distinct daughter cells. It is distinct from mitosis but overlaps with telophase.

Animal Cell Cytokinesis

Achieved by a cleavage furrow pinching the parent cell inward until it completely divides

Plant Cell Cytokinesis

Achieved by the formation of a cell plate (new membrane) at the metaphase plate that fuses with the existing plasma membrane.

Heredity

The transmission of traits from one generation to the next.

Variation

Differences between individuals

Genetics

The study of heredity and hereditary variation

Gametes

Reproductive cells that transmit genes from one generation to the next.

What is the ploidy outcome of asexual reproduction in eukaryotes?

• 1 diploid parent → 2 diploid offspring.

• 1 haploid parent → 2 haploid offspring.

(Produces genetically identical clones)

Advantages of Asexual Reproduction

Fast, less energy required, safe, lots of offspring, and keeps adaptations (no genome dilution)

Zygote

A diploid cell resulting from fertilization (the fusion of two gametes)

Advantages & Costs of Sexual Reproduction

• Advantage: Genetic variation (helps survival in environmental changes)

• Costs: Slower, higher energy requirement, dangerous, fewer offspring, and genome dilution

What problem arises if gametes have the same chromosome number as parents, and what is the solution?

• Problem: Chromosomes would double every generation

• Solution: Meiosis (reduction division that halves chromosome number)

What is the overall cellular yield of meiosis?

1 diploid cell → 4 haploid cells (gametes)

How many chromosomes and chromatids do human cells have as they enter meiosis?

46 chromosomes and 92 chromatids (following duplication in Interphase).

What is the main outcome of Meiosis I?

Homologous chromosomes separate, and the cell's ploidy is reduced from diploid to haploid

Synapsis

The pairing up of homologous chromosomes during Prophase I, resulting in a tetrad (2 homologous chromosomes / 4 chromatids)

Crossing Over (Homologous Recombination)

The exchange of genetic material between non-sister chromatids in a tetrad. An important source of genetic diversity.

How many chromosomes, tetrads, and chromatids are present at the end of Prophase I in humans?

46 chromosomes, 23 tetrads, and 92 chromatids.

Metaphase I

Tetrads align at the metaphase plate, with homologous chromosomes oriented towards opposite poles.

Anaphase I

Homologous chromosomes separate (disjunction) and move to opposite poles. Sister chromatids do not separate.

What is the final cell count and chromosome count at the end of Telophase I in humans?

2 haploid cells, each containing 23 chromosomes and 46 chromatids (chromosomes are still duplicated).

Interkinesis

A short, interphase-like stage between Meiosis I and Meiosis II. It features no S-phase and no DNA replication.

What occurs during Meiosis II?

Sister chromatids separate into daughter cells. This process is essentially identical to mitosis.

What are the 4 stages of Meiosis II?

Prophase II, Metaphase II, Anaphase II, and Telophase II (along with cytokinesis).

At the end of Meiosis II in humans, how many chromosomes, tetrads, and chromatids are in each cell?

• Chromosomes: 23 individual chromosomes.

• Tetrads: 0 (only exist in Meiosis I).

• Chromatids: 23 chromatids (no longer duplicated).