Chapter 18 Rev.

MAJOR TOPIC TWO

Chapter 18 Review: Patterns of Chromosome Inheritance
1. Chromosomes and the Cell Cycle
Chromosomes occur in pairs in the body’s cells. A karyotype is a visual display of a person’s chromosome. A normal human karyotype shows 22 homologous pairs of autosomes and one pair of sex chrom. The normal sex chrom. In males is XY, and in females XX. The cell cycle occurs continually and has 4 stages to it. G1, S, G2, M. In G1 a cell doubles organelles and accumulates materials for DNA synthesis. In stage S DNA replication occurs. N G2, a cell synthesizes proteins needed for cell division.
2. Mitosis
This is the duplication division that assures that all body cells have the diploid number & the same kinds of chromosomes as the cell that divides. Prophase: Chromosomes attach to spindle fibers. Metaphase: They align at the equator. Anaphase: Chromatids separate, becoming chromosomes that move toward the poles. Telophase: Nuclear envelope form around chromosomes, cytokinesis begins. Cytokinesis is the division of cytoplasm and organelles following mitosis.
3. Meiosis
This involves two cell divisions, I and II. In stage I, homologous chromosomes pair and then separate. In stage II, sister Chromatids separate, resulting in four cells with the haploid number of chromosomes that move into daughter nuclei. Meiosis is a part of a gametogenesis.
4. Comparison of Meiosis and Mitosis
They are both nuclear divisions but there are several differences between them. Meiosis only occurs at a certain time in the life cycle of sexually reproducing organisms. The events of meioses II are just like those of mitosis except in meiosis II the nuclei contain the haploid number of chromosomes. Meiosis is a part of spermatogenesis the production of sperm in males, and oogenesis in the eggs of a female.
5. Chromosomes Inheritance
Meiosis is a part of gametogenesis and contributes to genetic diversity. Nondisjuction changes the chromosome number in gametes, resulting in trisom or monosomy. Autosomal syndromes include trisomy and Down syndrome. No disjunction during oogenesis can result in gametes that have too few or too many X or Y chromosomes. The syndromes names are: Turner, Klinefelter, poly-x, and Jacobs.