Chapter Eight: The Cellular Basis of Reproduction and Inheritance

Questions:

1. What are the various steps of mitosis and meiosis?
2. What are the two methods of reproduction?
3. What is the difference between cytokinesis in plant and animal cells?

Answers:

1. The steps of mitosis are interphase, prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.  Meiosis first begins with meiosis I.  During meiosis I, prophase I, metaphase I, anaphase I, and telophase I all occur.  Meiosis II follows meiosis I without chromosome duplication.
2. The two methods of reproduction are asexual reproduction and sexual reproduction.  In asexual reproduction, offspring are identical to the original cell or organism.  The offspring also inherits all  its genes from one parent.  In sexual reproduction, offspring are similar to parents, but show variations in their traits and involve the inheritance of unique sets of genes from two different parents.
3. A ring of microfilaments pinches an animal cell in two, a process called cleavage.  In a plant cell, membranous vesicles form a disk called the cell plate at the midline of the parent cell, cell plate membranes fuse with the plasma membrane, and a cell wall grows in the space.  

Important Facts:

• Somatic cells have pairs of homologous chromosomes, receiving one member of each pair from each parent.  Homologous chromosomes are matched in length, centromere position and gene locations.  
• Cancer cells escape control on the cell cycle.  They divide rapidly, often in the absence of growth factors.  They spread to other tissues through the circulatory system.  The growth is not inhibited by other cells and tumors form.
• The factors that control cell division include: presence of essential nutrients, growth factors, proteins that simulate division, presence of other cells causes density-dependent inhibition, and contact with a solid surface, as most cells show anchorage dependence.
• Separation of homologous chromosomes during meiosis can lead to genetic differences between gametes.  Homologous chromosomes may have different versions of a gene at the same locus.  One version was inherited from the maternal parent, and the other came from the paternal parent.  Since homologues move to opposite poles during anaphase I, gametes receive either the paternal or maternal version of the gene.
• An imbalance in chromosome number results in Down Syndrome, which is characterized by characteristic facial features, susceptibility to disease, shortened life span, mental retardation, and variation in characteristics.

Key Terms:
Fertilization- the union of sperm and egg
Chromatin- DNA and proteins.
Cell Cycle- an ordered sequence of events for cell division.  Consists or interphase and Mitotic phase.
Interphase- duplication of cell contents.
Mitotic phase- division of cell.  Includes mitosis (division of the nucleus) and cytokinesis (division of cytoplasm)
Centrosomes- Structures in the cytoplasm that produce a mitotic spindle required to divide the chromosomes.  They organize micro-tubule arrangement and contain a pair of centrioles in animal cells.
Cell Cycle Control System- A set of molecules, including growth factors, that triggers and coordinates events of the cell cycle.
Diploid Cells- have two homologous sets of chromosomes.
Haploid Cells- have one set of chromosomes.
Nondisjunction- the failure of chromosomes or chromatids to separate during meiosis.


Relevant Diagram:  This diagram shows the whole process of meiosis.  Meiosis is the process of cell division in germ line cells to form gametes. This process furthers sexual reproduction because each gamete has half the number of chromosomes of normal cells, so that when two gametes (one from each parent) combine, the correct number of chromosomes is preserved in the resulting zygote organism. This process is unlike mitosis, where the cells are simply replicated, preserving the number chromosomes.

Relevant Video:
http://www.youtube.com/watch?v=BFWelOJ7fW0

Summary:
This chapter mainly discusses cell division/reproduction.  The chapter begins with mitosis, detailing first the role of chromosomes and then moving on to the different phases of mitosis.  It talks about cell cycle control and then moves on to meiosis and homologous chromosomes.  The many phases of meiosis are discussed in great detail.  The chapter then finishes with genetic variation and chromosome number which directly affects mutation.