Human Genome and Chromosome Quick Reference

DNA Length and Genome Size

• Approximately $6\ \text{ft}$ of DNA reside in a single human cell.
• Genome size per cell: $3.2\times 10^9\ \text{bp}$ (per haploid genome).
• In the nucleus, DNA is organized into chromosomes.

Chromosome and Chromatin Structure

• DNA wraps around histone proteins to form nucleosomes; nucleosomes fold into higher-order structures (chromatosomes, 30 nm fibre).
• Chromatin exists in two functional states:
  • Euchromatin: active gene regions.
  • Heterochromatin: less active/repressed regions.
• During cell division, chromatin condenses to form chromosomes.

Cell Cycle Basics

• Interphase includes:
  • $G_1$ (growth),
  • $S$ (DNA synthesis),
  • $G_2$ (pre-mitosis preparation).
• M phase = mitosis (and cytokinesis).
• Go = a non-dividing/resting state.

Karyotype and Chromosome Numbers

• Humans have $22\times\text{autosomes}$ in the nucleus (44 autosomes total in diploid cells).
• Plus sex chromosomes: $XX$ (female) or $XY$ (male).
• Mitochondrial DNA (MT) is separate from the nuclear genome.
• Normal human genome content (as shown in the slides): $58{,}517{,}616\ \text{bp}$ and $2{,}494\ \text{genes}$ (note: these figures are from the provided transcript).
• Karyotype pattern shown as: 1–22, X, Y (with XX or XY for sex).

Diploidy and Sex Chromosomes

• Humans are diploid: two sets of chromosomes per somatic cell.
• Di- two; Ploid - having a set number of chromosomes.
• Each somatic cell typically contains $44\text{ autosomes}$ + $2\text{ sex chromosomes}$ = $46\text{ total chromosomes}$.

Homologous Chromosomes and Alleles

• Homologous chromosomes: a pair consisting of one chromosome from each parent.
• They carry the same genes in the same order, but may carry identical or different alleles.
• Each homologous pair has centromeres and is inherited from one parent (mother) or the other (father).
• Homologous pair represents the genetic material that can be recombined during meiosis.

Chromosome Pairing in Reproduction

• Chromosome viewer concept: one chromosome from the egg (maternal) and one from the sperm (paternal) form a homologous pair.
• This pairing ensures genetic similarity and variation through alleles.

Mitosis vs Meiosis (Context from slides)

• Normal cellular activity primarily involves mitosis (cell division for growth/repair).
• Meiosis is a special division to produce gametes (not detailed here, but referenced on the slides).

Quick reference terms

• DNA double helix, Histones, Nucleosome, Chromatosome, 30 $\text{nm}$ fibre, Chromatin, Chromosome, Euchromatin, Heterochromatin.
• Interphase vs Metaphase; Chromosome condensation during division.
• $G<em>1, S, G</em>2, M, Go$: key cell cycle phases.
• $XX, XY, MT$: sex chromosomes and mitochondrial DNA.