Mitosis, Meiosis, and Chromosomal Anatomy

• The lecture covers Mitosis, Meiosis, and Chromosomal Anatomy
• The presentation date is January 27, 2025

Cell Genetic Information Packaging

• Prokaryotes lack a nucleus
• Prokaryotes are easier to read and copy DNA, and have either fewer or no complexes with histone proteins
• Eukaryotes have a nucleus along with other structures, histone, and other associated proteins
• Eukaryotes typically have more genes

Binary Fission

• Binary fission is a simpler process in prokaryotes

Eukaryotic Cell Division

• Eukaryotic cell division is a more complex process
• Mitosis and cytokinesis (cell division) transpire in the M phase
• After the G2/M checkpoint, cells can divide
• In G2, the cell gears up for mitosis
• In S, DNA duplicates
• Interphase is for cell growth
• During G1, cells grow
• Cells may enter G0 which is a non-dividing phase
• After the G1/S checkpoint, the cell is committed to dividing

Mitosis Basics

• Most cells are in interphase except those cells that need to continuously divide
• Prophase dissolves the nuclear envelope, and the spindle develops to pull newly condensing chromosomes
• Prometaphase sees microtubules latch onto chromosomes
• Metaphase aligns all chromosomes on the metaphase plate
• During anaphase, sister chromatids are pulled apart at the centromere
• Telophase occurs when chromosomes arrive in each newly separating cell, new nuclei develop, and cytokinesis takes place

Chromosome Count

• During mitosis, the number of chromosomes remains constant at 4, except during anaphase when it doubles to 8 before cytokinesis
• The number of DNA molecules doubles from 4 to 8 during the S phase and remains at 8 until telophase and cytokinesis, when it returns to 4

Meiosis

• Meiosis I and Meiosis II are the two major stages
• Interphase involves centrosome and chromosome duplication
• DNA is copied
• Prophase I sees chromosomes pairing up, where recombination occurs at the meiotic spindle
• During Metaphase I, chromosomes align at the equator
• Anaphase I sees paired chromosomes pulled apart
• During Telophase I and cytokinesis, the cell pinches in the middle, forming two daughter cells
• Prophase II generates two daughter cells
• Metaphase II sees chromosomes aligning at the equator
• During Anaphase II, sister chromatids are pulled apart
• Telophase II and cytokinesis involves the cell pinching to produce four granddaughter cells
• n = haploid, 2n = diploid

Meiosis - Chromosome Number Reduction

• Meiosis halves the chromosome count during cell division
• If a parent cell contains four chromosomes, the granddaughter cells will have two

Genetic Diversity

• During Prophase I segments of nonsister chromatids are exchanged
• After Meiosis I and II, each of the resulting cells carries a unique combination of alleles

Chromosome Anatomy

• Chromosome behavior during meiosis explains Mendelian inheritance
• Chromosomes come in homologous pairs
• Chromosome pairs separate at meiosis so that each gamete gets one copy

Chromosome Packages

• Mitosis involves both parent and daughter cells that are 2N (diploid)
• Replicated chromosomes divide into daughter cells
• Mitosis happens over a single cell division
• Meiosis involves making gametes over two cell divisions
• Gametes are N (haploid)
• During Meiosis I, homologous chromosomes line up and recombine, dividing into haploid daughter cells
• During Meiosis II, recombinant chromatids are pulled into each daughter cell
• Progenitor cells measure 2N (diploid)

Chromosome Anatomy in Detail

• Chromatids consist of a single long strand of DNA
• Chromosomes start as one chromatid, then get copied into two sister chromatids and pulled apart into two daughter chromatids
• Chromatin denotes a general term for the DNA and the proteins that make up chromosomes
• Every chromosome has a centromere
• The cytoskeleton attaches to the centromere to pull chromatids apart in mitosis and meiosis
• Chromosomes can be categorized based on their centromere position (metacentric, submetacentric, acrocentric)
• Telomeres are at the end of each arm of a chromosome
• Karyotypes represent an individual's set of chromosomes, recognizable as pairs when a cell is divided during mitosis
• Giemsa stain visualizes chromosomes, targeting the phosphate backbone of DNA and reveals bands of GC-rich and AT-rich regions
• Chromosomes are single molecules of DNA packaged into proteins
• During mitosis and meiosis, chromosomes condense into tight packages
• During interphase chromosomes are diffuse, though DNA continues to remain organized around proteins

Lecture on Mitosis, Meiosis, and Chromosomal Anatomy. Includes cell genetic information packaging and eukaryotic cell division. Covers the differences between prokaryotes and eukaryotes, binary fission, and the basics of mitosis.