Chapter 11 & 12 Work - Genetics

Derek Lee

Mr. Hillegas

Ap Biology

14 February 2011

Chapter 11 & 12 Work

II. Connections

a.       Gene locus & disulfide bridge- The gene locus is the location for a specific gene on a chromosome which might code for making a specific protein. If the protein undergoes tertiary or proceeds to quaternary folding, further folding into a specification 3D conformation takes place as a result of disulfide bridges, which form between sulfur atoms in neighboring cysteine amino acids.

b.      Nondisjunction & 9-triplet pattern- MTOC’s (Basal Bodies and centrioles/centrosomes) which consist of  microtubules in a 9+3 pattern are responsible for making up the spindle used in separating chromosomes during mitosis and meiosis. Aneuploidy (having one extra or one less chromosome) results from nondisjunction, whereby one or more pairs of chromosomes do not separate as they should during mitosis or meiosis. Thus down syndrome results when a cell does not separate the correct amount of chromosomes into its cell and fails to commit apoptosis.

c.       Autosome & Steroid- As a result of nondisjunctions with autosome chromosomes, alterations occur during the development of certain phenotypes. For example in XXY males who make less testosterone and more estrogen than normal males which may result in short0term memory, learning disabilities, feminizing effects, low sperm counts, high pitched voice, etc. These individuals may receive testosterone injects –sterioids- in order to reverse the feminizing effects.

d.      Polygenic & Glycocalyx- Polygenetics pertain to the combined action of alleles of more than one gene, some traits, which are predispositions to different heart diseases, hypertension, etc as a result of genetic disorders. The glycocalyx also includes the cell-adhesion molecules that enable cells to adhere to each other and guide the movement of cells during embryonic development. It functions for protection, immunity to infection, defense against cancer, transplant compatibility, cell adhesion, inflammation regulation, fertilization, and embryonic development which are important to preventing genetic disorders leading to a variety of polygenic diseases.

III.  The law of segregation says that alleles in homologous chromosomes separate or segregate during gamete formation and unite at fertilization.  It consists of diploid cells that have pairs of genes on homologous chromosomes. The 2 genes of the pair will separate from each other during meiosis and thus be separated into different gametes. The law of independent assortment says that alleles in nonhomologous chromosomes will separate during the formation of gametes. When meiosis ends, and the pairs of homologous chromosomes have migrated to opposite poles. The chromosome which goes to which pole depends on its previous orientation which is random. This results in traits and chromosomes which are inherited independently/transmitted to the offspring independently despite previously  beings gene pairs. After meiosis the law of segregation deals with gametes with one version of each chromosomes which come together to form the zygote with one gene from each parent while the law of independent assortment occurs during metaphase till meiosis ends resulting in an independent distribution of chromosomes.

Chapter 10 Mitosis/Meiosis Work

Derek Lee

Mr. Hillegas

Ap Biology

4 February 2011

Chapter 10 Cell Reproduction Work

II.

1.      Homologous and duplicated chromosomes – Together with 23 chromosomes from each parent, 23 homologous pairs are formed. These homologous pairs are duplicated in the processes of mitosis or meiosis for either cellular reproduction, growth, and repair, or sexual reproduction. The results of mitosis form 2 somatic diploid cells, while meiosis results in 4 autonomic haploid male or female gametes.

2.      Kinetochore and Microtubule Organizing Center – During Metaphase I of meiosis when the tetrads line up long the metaphase plant, spindle fibers forms and MTs attach to kinetochores. These kinetochores shorten pulling apart the tetrads to opposites poles as the microtubules deploymerize.

3.      Haploid and Somatic – Somatic cells include all cells except sex cells. They are the cells which undergo mitosis for cell reproduction, growth, and repair as opposed to autonomic, or sex cells which undergo mitosis, thus producing 4 gametes with a haploid number of chromosomes.

4.      Nucleosome and Dehydration reaction- Nucleosomes consist of subunits of chromatin composed of a short length of DNA wrapped around a core of histone proteins. Dehydration reactions or condensation reactions refer to the use covalent bonds to join two molecules into a larger  molecule. These bonds help coil histones as they form bonds between peptide bonds.

III. Sorting of Chromosomes

A.    Meiosis I

1.      Prophase 1- Chromosomes become visible as threadlike forms, each pairs with its homologue and swaps segments with it.

a.       Microtubules form spindles, centrioles (if present) move to opposite sides of nuclear envelope.

b.      Nuclear envelope begins to break up

2.      Metaphase I – MTs attach to each type of chromosome, chromosomes line up at metaphase plate.

a.       MTs begin to pull apart chromosomes

3.      Anaphase I – Microtubules attached to each chromosome shorten and move toward spindle pole

a.       Other MTs extend from poles and overlap at equator and push the poles father apart

b.      Pushing driven by proteins

4.      Telophase I – On of each type of chromosome on complete opposite sides of poles.

a.       At some point the cytoplasm dives forming two haploid cells

b.      All chromosomes are still duplicated

B.     Meiosis II

1.      Prophase II- Spindle forms in each haploid cell while MTs move one member of pair of centrioles to opposite sides of each cell.

a.       MTOCs attach to one chromatid of each chromosome.

b.      Its sister chromatid becomes tethered to opposite pole

2.      Metaphase II – Chromosomes line at metaphase plate and MTs from both spindle poles begin to separate the sister chromatids

3.      Anaphase II – Attachment between sister chromatids of each chromosome breaks

a.       Each MTs continue to move chromosomes to opposite sides of the poles while MTs push the poles apart.

b.      Chromosomes ends up near each pole, one of each type of chromosome is present in each parcel

4.      Telophase II – Four nulei form as a new nuclear e nvelope encloses each cluster of chromosomes

a.       After cytoplasmic division each of the daughter cells has a haploid number of chromosomes.

10.4 –

A. During prophase I of meiosis the duplicated chromosomes in a germ cell are in a thread like form with little space in between.                                                                                                    1. This tight, parallel orientation favors crossing over, a molecule interaction between a chromatid of one chromosomes and a chromatid of the homologous partner.                                     2. The DNA strands break and seal in such a way that the outcome results in two “nonsister” chromatids which leads to recombination among genes of homologous chromosomes.                             3. This results in slightly different forms of alleles and thus each crossover event is a chance to swap slightly different versions of heritable information on gene products or produce variation in traits among offspring.

B. Metaphase I Alignments                                                                                                                            1. During Metaphase I, Microtubules from both poles now align all duplicated chromosomes at the metaphase plate.                                                                                                                       2. MTs attach to first chromosome they contact = random tethering and subsequent positioning of each pair of maternal and paternal chromosomes at metaphase plate.                                     3. During Anaphase I, duplicated chromosomes = move away from homologous partner = either partner can end up at either spindle pole.                                                                                             4. Result of such events leads to different combination of maternal and paternal traits in each new generation.

10.6

While Mitosis maintains the parental chromosome number, meiosis halves it, to the haploid number. Miotic cell division is the basis of asexual reproduction among eukaryotes. It is the basis of growth and tissue repair of multicelled eukaryotic species. Meiotic cell division is a required step before the formation of gametes or sexual spores.

Similarities: Both processes undergo prophase, metaphase, anaphase, and telophase with similar processes and organelles i.e. MTOCs, spindle fibers, etc. Both have cytokinesis that occurs during telophase. Mitosis and meiosis only occurs in eukaryotic cells.

Differences: Occurrence of crossing over happens in meiosis but does not happen in mitosis.

-Meiosis occurs specifically in humans, animals, plants, and fungi, while mitosis happens in all organisms.

-Meiosis produces 4 daughter cells (4 haploid) while mitosis produces 2 (2 diploid) daughter cells.

-Meiosis produces genetic variation, is sexual reproduction, requires 2 divisions, pairs homologues and undergoes two series of prophase, metaphase, anaphase, and telophase. Mitosis produces identical genes, is asexual reproduction, undergoes 1 series of division, does not pair homologues, and undergoes one series of prophase, metaphase, anaphase, and telophase.

-Meiosis produces male and female eggs/sperms while mitosis produces all cells other than sex cells