BI226 Chapter 4: Chromosome Theory of Inheritance
Document Summary
Down syndrome is attributable to an abnormal number of chromosomes. The type and amount of genetic material is important for normal development. Microscopy revealed that semen contain spermatozoa (sperm animals) Hypothesized that the sperm may enter the egg to achieve fertilization. Direct observations of fertilization through union of nuclei of eggs and sperm (frog and sea urchin) Conclusion: something in the nucleus must contain the hereditary material. Long, threadlike bodies (chromosomes) visualized in the nucleus. Movement of these bodies followed through cell division. Mitosis - nuclear division that generates two daughter cells containing the same number and type of chromosomes as a parent cell. Meiosis - nuclear division that generates gametes (egg and sperm) containing half the number of chromosomes found in other cells. Most body cells are diploid (2n) (each chromosome pair has one maternal and one paternal copy) Fertilization is the union of haploid gametes to produce diploid zygotes.
