Lecture_17_-_Mitosis_and_Meiosis_2024
Introduction to Genetics
Understanding Mitosis and Meiosis
Key Questions to Address:
Definitions of DNA, chromosomes, genes, alleles, heritable traits, genotypes, and phenotypes.
Relationship between genetic information and heritable traits.
Concept of homologous chromosomes and the definition of "diploid".
Genetic Information and Heritable Traits
DNA
Defined as a molecule containing genetic instructions for protein production.
Sequence of nitrogenous bases determines protein synthesis.
Chromosomes
Chromosomes consist of DNA molecules.
Each chromosome contains many genes.
Genes and Alleles
Gene: A segment of DNA that encodes for a specific protein or trait.
Allele: A variant form of a gene differing in base sequence.
Variations in alleles create diversity in heritable traits within a population.
Genotype and Phenotype
Genotype: The specific sequence of nitrogenous bases, which determines the corresponding allele.
Phenotype: The observable physical trait or characteristic resulting from the genotype.
Chromosomal Basics
Chromosome Structure
Eukaryotic species have varying chromosome numbers.
Most organism's chromosomes exist in pairs, referred to as diploid (2n).
Homologous chromosomes: Pairs of chromosomes that are similar in size, shape, and gene content, but may carry different alleles.
Example: Drosophila (fruit fly) has 4 pairs of chromosomes.
The Process of Mitosis
Overview
Mitosis occurs in all eukaryotic cell types, excluding germ cells.
It results in the production of new somatic cells and is essential for growth and asexual reproduction.
Outcomes of Mitosis
Produces two genetically identical daughter cells from one parent cell.
Critical for embryonic development and cell replacement in somatic tissues.
Stages of Mitosis
Interphase - Preparation phase where chromosomes replicate.
Prophase - Chromatids condense; spindle apparatus begins to form.
Metaphase - Chromosomes align at the center of the cell.
Anaphase - Sister chromatids are pulled apart to opposite poles.
Telophase - Nuclear envelope reforms, and chromosomes de-condense.
Cytokinesis - Cytoplasm divides, completing the formation of two daughter cells.
The Process of Meiosis
Overview
Meiosis occurs in germ cells to produce gametes (sperm and eggs).
Involves two rounds of cell division, resulting in four daughter cells, each haploid (n).
Outcomes of Meiosis
Produces male (sperm) and female (egg) gametes with half the chromosome number of the parent cell.
Crucial for sexual reproduction and genetic diversity.
Mechanisms of Genetic Diversity
Crossing Over: Exchange of genetic material between homologous chromosomes during prophase I.
Independent Assortment: Random distribution of maternal and paternal chromosomes to daughter cells during metaphase I.
Stages of Meiosis
Interphase - Chromosomes replicate in the parent cell.
Prophase I - Homologous chromosomes pair and exchange segments.
Metaphase I - Chromosomes align at the equator.
Anaphase I - Homologous chromosomes are pulled to opposite poles.
Telophase I and Cytokinesis - Nuclear membranes reform and the cell divides.
Meiosis II - Similar to mitosis but results in four haploid cells.
Comparison: Mitosis vs. Meiosis
Advantages of Mitosis
Produces genetically identical offspring quickly.
Essential for growth and tissue repair.
More efficient under stable environmental conditions.
Advantages of Meiosis
Generates genetic diversity through sexual reproduction.
Enhances survival through varied offspring in changing environments.
Conclusion
The processes of mitosis and meiosis are integral to the life cycle of organisms.
Understanding these concepts is crucial for studying genetic inheritance and evolutionary biology.