Science Olympiad: Designer Genes 2025-2026

Mitosis

makes 2 identical cells, for growth and repair

Meiosis

makes 4 genetically unique cells, for reproduction

Prophase

• Chromatin condenses → forms visible chromosomes (X-shaped, 2 sister chromatids).

• Mitotic spindle forms from centrioles (microtubule skeleton).

• Nuclear envelope breaks down, nucleolus disappears.

• Spindle fibers attach to kinetochores on centromeres.

Metaphase

• Chromosomes line up along the metaphase plate (center of the cell).

• Spindle checkpoint ensures all chromosomes are attached correctly.

Anaphase

• Sister chromatids separate → pulled to opposite poles by spindle fibers.

• Microtubules not attached to chromosomes push poles apart, elongating the cell.

Telophase

• Chromosomes decondense back into chromatin.

• Nuclear envelope reforms, nucleoli reappear.

• Mitotic spindle breaks down.

Cytokinesis

Division of cytoplasm → results in 2 identical daughter cells.

Cleavage Furrow

how animal cells split

Cell plate

how plant cells split

Prophase, Metaphase, Anaphase, Telophase

Phases of Mitosis in order

Crossing over

homologous chromosomes swap segments → genetic variation

Spermatogenesis

Sperm → all 4 cells usable

Oogenesis

Egg → 1 viable egg + 3 polar bodies

Polysomy

extra chromosomes

Monosomy

missing chromosomes

Addition mutation

extra nucleotides

Deletion mutation

missing nucleotides

Translocation mutation

chromosome pieces swap

Direct reversal

fixes UV damage

Excision repair

removes damaged nucleotides

Post-replication repair

replication bypasses damage, fixes gap later

Transcriptional

control RNA polymerase access

Post-transcriptional

RNA splicing, alternative splicing, Poly-A tail, 5’ cap

Translational

Lac operon (inducible), Trp operon (repressible)

Post-translational

folding (chaperonins), modifications (glycosylation, phosphorylation)

miRNA

silences gene expression

Epigenetics

chemical marks turn genes on/off without changing DNA

Epistasis

one gene masks another

Hardy-Weinberg equilibrium conditions

no mutation, no migration, large population, no natural selection, random mating

p²

homozygous dominant in equations is represented by

2pq

heterozygous in equations is represented by

q²

homozygous recessive in equations is represented by

DNA sequencing

Sanger (old, precise), NGS (fast, cheap)

RNA-Seq

measures RNA expression

PCR

amplifies DNA

Gel electrophoresis

separates DNA/proteins by size/charge

Blotting (SNoW DRoP)

Southern = DNA, Northern = RNA, Western = protein

CRISPR-Cas9

guide RNA → Cas9 cuts DNA → repair or replacement

Plasmid cloning

small DNA circles carry genes into cells

Gene therapy

replace or fix faulty genes (experimental, risky)

Belmont Report principles

Respect, Beneficence, Justice

Prophase I

• Chromosomes condense and become visible.

• Homologous chromosomes pair up → form tetrads (4 chromatids).

• Crossing over occurs → exchange of DNA segments between homologues → genetic variation.

• Spindle fibers form, nuclear envelope breaks down.

Metaphase I

• Tetrads line up

• Random alignment → independent assortment → increases variation.

Anaphase I

• Homologous chromosomes are pulled apart to opposite poles.

• Sister chromatids stay together.

Telophase I & Cytokinesis

• Nuclear envelope may reform; chromosomes may decondense.

• Cytoplasm divides → 2 haploid cells.

Result of Meiosis 1

Each cell has one chromosome from each homologous pair, but still with two sister chromatids.

Prophase II

• Chromosomes condense again (if they had decondensed).

• Spindle fibers form, nuclear envelope breaks down.

Metaphase II

• Chromosomes line up individually.

Anaphase II

• Sister chromatids are now separated and pulled to opposite poles.

Telophase II & Cytokinesis

• Nuclear envelopes reform, chromosomes decondense.

• Cytoplasm divides → 4 haploid cells, each genetically unique.

Interphase

• Most cells spend 90% of their time here.

• G1 (Gap 1): Cell grows, makes proteins, duplicates organelles.

• S (Synthesis): DNA is replicated → each chromosome now has 2 sister chromatids.

• G2 (Gap 2): Cell grows more, checks DNA replication, repairs mistakes.

• Checkpoints: G1 and G2 ensure DNA is intact and the cell is ready to divide.