Chapter 15: The Eukaryotic Cell Cycle, Mitosis, and Meiosis

Summary:

Introduction:

• Cell division is the reproduction of cells
• highly regulated process
• in mitosis, daughter cells receive the same amount of genetic material as the mother cells
• in meiosis,  the daughter cells get half the genetic material
• needed for sexual reproduction

Section 15.1

• Cytogenetics is the field of genetics that involves the microscopic examination of chromosomes and cell division
• A karyotype is a photographic representation of the chromosomes
• Types of chromosomes
• sex chromosomes
• determine the sex of the individual; are different for males and females
• autosomes
• the remaining chromosomes that aren't sex chromosomes
• Sets of chromosomes
• if there are two sets of chromosomes, the cell is diploid
• members of each pair of chromosomes are called homologues 
• with one set, it's haploid
• gametes, the sex cells, are haploid
• Eukarytoic cells that are going to divide go through the cell cycle in multiple steps
• G1 - cell growth occurs; cell decides if it's going to divide or not
• S - chromosomes are replicated 
• G2 - proteins required for division are made; cell growth occurs
• M - the cell divides
• Checkpoints in the cell cycle determine if the cell is ready to divide
• they also check if everything is going smoothly and as planned

Section 15.2 

• Mitotic cell division is the process of cells dividing to form two daughter cells with identical genetic information to the mother cell
• is used in asexual reproduction, a form of reproduction without two gametes fusing together; only a single parent is needed
• Process
• Interphase - the cell goes through G, S, and G2 stages of the cell cycle; chromosomes are decondensed
• Prophase - chromosomes are already replicated and joined as sister chromatids; nuclear envelope dissapears; chromatids condense
• Prometaphase - mitotic spindle forms; 
• Metaphase - Chromosome pairs line up in the center of the cell, in a single row
• Anaphase - sister chromatids are split and pulled to opposite sides of the cell
• Telophase - chromosomes reach opposite sides of the cells and decondense; nuclear envelopes reform and create two separate nuclei
• Cytokinesis - the cell splits forming two separate daughter cells

Section 15.3

• Sexual reproduction
• two haploid gametes fuse to form a diploid zygote
• this process is called fertilization
• Meiosis is used for this
• forms haploid daughter cells
• can have crossing over, where information is exchanged between chromosomes
• Meiosis I
• first part of meiosis
• similar to mitosis
• separates homologues from each other
• Meiosis II
• cell is already split into 2
• now sister chromatids are split
• this makes the cell haploid

15.4

• Chromosome structure and number
• centromeres can be placed at different locations
• mutations can occur
• some species can have different numbers of chromosomes
• humans are diploid (2n), but 
• In some species, such as bees, one gender has a haploid number and the other a diploid number
• Changes can result in abnormalities
• extra chromosomes in humans can result in diseases such as Down syndrome, and cause physical and mental impairments

Interesting Stuffs

Animation: Down Syndrome

http://media.jeffersonhospital.org/videos/animation-down-syndrome?quicktabs_1=0

Down syndrome occurs when there's an extra copy of the chromosome number 21 in a human. While it causes many physical effects, you can be certain by looking at the karyotype of the individual and seeing the extra chromosome. This is called a trisomy. There is no known cause for it, but a pattern can be seen when you look at older woman who give birth. They're more likely to have a down syndrome child. Down syndrome is discussed in section 15.4.

Video: Mitosis

http://www.youtube.com/watch?v=VlN7K1-9QB0

Chromosomes replicate, the nuclear envelope disappears, spindle fibers attach to chromosomes, they line up in the center of the cell, they get pulled to opposite sides of the cell, the nuclear envelopes reform, and the cell splits. You know the drill. And if you don't, look at my summary of section 15.2!!!

Article: Sex determination in the hymenoptera.

http://www.ncbi.nlm.nih.gov/pubmed/17803453

Hymenoptera is an "order" of species, which is all these insect buggy thingys, such as bees. They're unusual when it comes to chromosomes in the sense that males and females are different. Males have a haploid number of chromosomes, and females have a diploid number of chromosomes. This is because females are better. Females are special -- they come from the eggs that the males thought were important enough to fertilized. The unspecial, unimportant, unwanted leftover eggs turn into males. but apparently, you can get diploid males, too! ...if you inbreed. This kind of crazy stuff is discussed in section 15.4.