Tiêu đề cell cycle.pdf ✅

HUMAN HISTOLOGY LECTURE NOTES / PRELIMS 2 MISSYNOTES Stem cells: are unspecialized cells endowed with two crucial properties: the capacity for self-renewal and the ability to generate specialized progeny • SELF RENEWAL: capacity of a stem cell to divide and produce at least one daughter cell that retains the same stem-cell properties remaining undifferentiated and capable of further divisions • SPECIALIZED PROGENCY: Differentiation refers to a stem cell’s ability to give rise to specialized cells— cells with distinct structures and functions not inherent to undifferentiated stem cells PROGENITOR CELLS: intermediate cells that arise from stem cells and are on a defined path toward differentiation. Unlike stem cells, which are undifferentiated and can often divide indefinitely, progenitor cells are partially committed and have limited self-renewal capacity. a specialized process involving two unique and closely associated cell divisions that occurs only in the cells that will form sperm and egg cells 2 CORE FEATURES: 1. Synapsis and Crossing-Over Early in the process, each pair of homologous chromosomes, one inherited from the mother, one from the father, pair up via a process called synapsis. During synapsis, double-stranded DNA breaks and repairs occur, leading to reciprocal genetic exchanges (crossovers) between the aligned homologues. a. These exchanges create new gene combinations, ensuring that no two germ cells carry identical chromosomes to those of the parents. 2. Reduction to Haploid Cells outcome of meiosis: formation of haploid cells, each containing a single member of each chromosome pair from the diploid somatic complement. a. Upon fertilization, the haploid sperm and egg unite to form a diploid zygote, restarting the full chromosomal set in the new individual. Key Chromosomal Events (Referencing Figure 3–18) • A cell preparing for meiosis has just completed DNA replication (S phase), so each chromosome now comprises two identical sister chromatids, held together by cohesin proteins. • Prophase I (greatly extended): Chromatin condenses, and homologues align and synapse. Because each homolog has two chromatids, such aligned structures called tetrads, represent four chromatids. During synapsis, crossovers occur, creating genetic recombination. o Crossing-over occurs at this stage, producing recombinant chromosomes visible as chiasmata. STEM CELLS AND TISSUE RENEWAL MEIOSIS