Medical Biology Lecture 5: Meiosis PDF

University of Al-Ameed College of Medicine Medical Biology Lecture 5 MEIOSIS ASSIST. PROF. DR. AHMED ZUHAIR ALWAELI 2023-2024 Introduction • Welcome to today's lecture on meiosis, a fundamental process in cell biology essential for sexual reproduction and genetic diversity. • Meiosis is a hig...

University of Al-Ameed College of Medicine Medical Biology Lecture 5 MEIOSIS ASSIST. PROF. DR. AHMED ZUHAIR ALWAELI 2023-2024 Introduction • Welcome to today's lecture on meiosis, a fundamental process in cell biology essential for sexual reproduction and genetic diversity. • Meiosis is a highly orchestrated mechanism, crucial for the formation of gametes and ensuring genetic variability in offspring. Objectives of the Lecture • Upon completing this lecture, students will be able to: • Understand the Phases of Meiosis: • • • • • • • • Describe the key events in each phase of meiosis, from prophase I to cytokinesis. Recognize the dynamic changes in cellular components during meiosis. • Explore Meiosis in Health: Understand the physiological roles of meiosis in sexual reproduction and genetic diversity. Appreciate how meiosis contributes to the maintenance of genetic variability. • Examine Diseases Related to Meiosis: Investigate how dysregulation of meiosis contributes to genetic disorders. Explore conditions resulting from errors in meiosis, such as aneuploidyrelated disorders. • Consider Meiotic Abnormalities and Therapeutic Opportunities: Examine current therapeutic strategies targeting meiosis-related conditions. Discuss potential future developments in drug development aimed at modulating meiotic processes. Overview of Mitosis • Definition: Meiosis is the process of cell division that results in four nonidentical daughter cells, each with half the number of chromosomes of the parent cell. Phases of Meiosis Phases of Meiosis: • Meiosis I Prophase I, Metaphase I, Anaphase I, Telophase I, • Meiosis II Prophase II, Metaphase II, Anaphase II, Telophase II (PMAT x2). Cytokinesis: The division of the cytoplasm following meiosis, resulting in four separate daughter cells. • . Phases of Meiosis- Prophase I • Prophase I is divided into a series of substages which are named according to the appearance of chromosomes. • Leptotene • Zygotene • Pachytene • Diplotene • Diakinesis Phases of Meiosis- Prophase I Homologous Chromosome Pairing: Chromosomes align with their homologous partners during prophase I. • Crossing Over: Exchange of genetic material between homologous chromosomes, enhancing genetic diversity. • Synapsis: The close association of • Phases of Mitosis – Metaphase I Homologous Chromosomes Align at the Metaphase Plate: Chromosomes align at the metaphase plate in pairs. • Independent Assortment: Random distribution of homologous chromosome pairs to daughter cells, contributing to genetic diversity.. • Phases of Mitosis – Anaphase I Homologous Chromosomes Separate: Homologous chromosome pairs separate and move to opposite poles. • Reduction Division: The number of chromosomes in each daughter cell is reduced by half. • Phases of Mitosis – Telophase I Chromosomes Reach Opposite Poles: Chromosomes reach the poles, and nuclear envelopes may reform. • Cytokinesis: The division of the cytoplasm occurs, resulting in two haploid daughter cells. • Phases of Meiosis - Prophase II • Chromosome Condensation: Chromosomes condense again in preparation for the second meiotic division. • Nuclear Envelope Breakdown: Nuclear envelope dissolves, allowing spindle fibers Phases of Meiosis - Metaphase II Chromosomes Align at the Metaphase Plate: Chromosomes align individually at the metaphase plate. • Spindle Fibers Attach: Spindle fibers attach to the centromeres of individual chromosomes. • Phases of Meiosis - Anaphase II Sister Chromatids Separate: Sister chromatids separate and move towards opposite poles. • Chromosome Movement: Spindle fibers shorten, pulling chromatids toward the centrosomes. • Phases of Meiosis - Telophase II Nuclear Envelope Reformation: Chromatids reach opposite poles, and nuclear envelopes begin to reform. • Cytokinesis: Division of the cytoplasm occurs, resulting in four haploid daughter cells. • Comparison with Mitosis: • While both are forms of cell division, mitosis results in two identical daughter cells diploid (2n), while meiosis yields four non-identical cells with half the chromosome number haploid (1n). Mitosis in Health Genetic Diversity in Offspring: Meiosis ensures the production of genetically diverse gametes, contributing to the variability of the offspring. • Evolutionary Significance: The genetic diversity generated by meiosis contributes to the adaptation and evolution of species over time. • Diseases Related to Meiosis Genetic Disorders: • Errors in meiosis can lead to aneuploidy, where cells have an abnormal number of chromosomes. • Examples include Down Syndrome and Turner Syndrome. • Aneuploidy: Abnormal chromosome numbers due to errors in meiosis. • Diseases Related to Meiosis • • • • • • • • Genetic Disorders: Nondisjunction Down syndrome – trisomy of chromosome 21 Patau syndrome – trisomy of chromosome 13 Edwards syndrome – trisomy of chromosome 18 Klinefelter syndrome – extra X chromosomes in males – i.e. XXY, XXXY, XXXXY, etc. Turner syndrome – lacking of one X chromosome in females – i.e. X0 Triple X syndrome – an extra X chromosome in females Jacobs syndrome – an extra Y chromosome in males. Clinical Diagnosis and Genetic Counseling Diagnostic Methods for Meiotic Errors: • Techniques such as karyotyping and genetic testing enable the identification of meiotic abnormalities. • Meiotic Abnormalities and Therapeutic Opportunities Targeting Meiotic Pathways: Understanding meiotic processes is essential for developing therapeutic strategies against meiosis-related conditions. • Meiosis as a Therapeutic Target: Opportunities for developing drugs that selectively modulate meiosis in genetic disorders. • Conclusion Meiosis is a fundamental process crucial for sexual reproduction, ensuring genetic diversity in offspring. • Dysregulation of meiosis can lead to genetic disorders, emphasizing the importance of understanding meiotic processes in clinical contexts. • Ongoing research into meiotic pathways offers potential therapeutic avenues for mitigating diseases related to meiotic abnormalities. • Questions and Homework What are the key phases of meiosis, and how does each phase contribute to the formation of genetically diverse gametes? • Can you explain the significance of crossing over and synapsis during meiosis? • How do errors in meiosis contribute to genetic disorders, and can you provide examples? • • Thank you for your attention. It's time for questions and discussion.