University:
Eastern Kentucky University
Course:
BIO 318 | General Botany
Academic year:

2020
Views:

442

Pages:

2
Author:

Edgar Rowe

Chapter 4 : Cell reproduction Mitosis (Chapter 3 in the textbook) Cell division is needed for growth, asexual reproduction and to replace dead cells. Cell cycle Fig 3.16.: Interphase (where the cell grows and DNA replicates) is followed by Mitosis ( where the cell divides into two ). Stages of Mitosis Prophase : the spindle (made of microtubules) forms. The spindle will control the movement of the chromosomes. The chromosomes are visible scattered at random. Metaphase : the chromosomes line up in the center of the cell. Anaphase : the centromeres divide. The chromosomes move to opposite ends of the cell ( many chromosomes form a V shape ). Telophase : two nuclei form. The cytoplasm divides ( cytokinesis ). Animal cells divide from the outside towards the center, plant cells divide from the center outwards. Reproduction and Meiosis Diploid cells - have two sets of chromosomes ( 2n ). Fig 12.6. Examples leaf, root, stem. Haploid cells - have one set of chromosomes ( n ). Examples sperm (or pollen) and egg. Comparison of Mitosis and Meiosis Mitosis Meiosis One cell division Two cell divisions One cell produces 2 cells One cell produces 4 cells No pairing Chromosomes pair up in Prophase I No crossing over Crossing over occurs Chromosome number unchanged Chromsome number halved in Anaphase I Produces diploid cells Produces haploid cells eg leaf eg sperm or egg Alternation of generations The sporophyte is a diploid plant which produces spores by meiosis. Each spore is haploid and will grow into a haploid gametophyte. The gametophyte produces sex cells (gametes) by mitosis. Once the sperm fertilizes the egg you have a diploid zygote (fertilized egg), which will grow into a diploid sporophyte again.