Chapter 11 and 12: Inheritance VISIBLE VERSION! yay

II. Connections

a. The locus of a gene is the specific area of a gene, which is read and copied by proteins in order for the ribosomes to produce new proteins. The shape and structure of these proteins, while influenced by interactions between amino acids and interactions between ‘r’ groups, is determined by disulfide bridges, which are covalent bonds between two cysteine amino acids.

b.  Nondisjunction is the failure of sister chromatids or homologous chromosomes to move apart and separate during meiosis or mitosis.  This can happen due to the centromeres and centrioles, which are arranged in a nine-triplet pattern, leaving the chromosomes stuck together and not moved into each cell that is a product of the process.

c. Autosomes essentially are all chromosomes except the sex chromosomes X and Y, which differ in males and females. This difference in gender is accompanied by the effects of steroids because some steroids, such as estrogen and testosterone, also differentiate between males and females in terms of molecule concentration.

d. Polygenic refers to traits that are determined by a specific number of genes, which allow for diversity within populations. An example of such would be the glycocalyx because, in eukaryotic cells, depending on the genes, they take a specific shape that allows the cell to which it is attached to interact with specific cells and have a unique identity.

III. Essentials

a.  Mendel’s  Law of Segregation states that, during metaphase I of meiosis, homologous pairs of chromosomes are separated, resulting in the gametes of the organism only containing one version of each chromosome. Ultimately, the offspring created by the fertilization of two gametes will contain two versions of each gene, resulting in an increased diversity within the population. Mendel’s Law of Independent Assortment states that in metaphase I of meiosis, when homologous chromosomes temporarily attach to each other at the chaism and form a tetrad, which chromosome faces which "pole" of the meiotic cell is completely random. In other words the maternal version of chromosome # 5 can be facing the right pole while the maternal version of chromosome #6 can be facing the left side of the cell. This, just like the Law of Segregation, creates variety and diversity within a population.

Chapter 10 Notes

II. Connections

1.  Homologous chromosomes are nonidentical sex chromosomes that have the same length, shape, and assortment of genes that line up with each other during meiosis.  Duplicated chromosomes are DNA strands that are replicated and stay attached at the centromere.

2.  Kinetochore is a mass of protein and DNA in the centromere to which microtubules of the spindle attach.  These microtubules which pull apart the connected chromatids are directed by microtubule organizing centers which dictate how microtubules will be organized and oriented in a given type of cell.

3.  Somatic cells are also known as body cells which,, after mitosis, result in the creation of 2 diploid cells with two sets of chromosomes each.  In reproductive sex cells, however, meiosis results in 4 haploid cells or gametes that contain only one set of chromosomes.

4. Nucleosomes are repeating subunits of chromatin occurring at intervals along a strand of DNA that are coiled around histones.  Dehydration reactions are dangerous to these nucleosomes as they can disrupt, uncoil, and destroy the DNA structure.

III. Essentials

a.       Prophase I

Chromosomes become visible and pair with their homologue. Microtubules begin to form, nuclear envelope starts to breakup

b.      Metaphase I

Mics. Connect to both chromosomes and homologous pairs. Chromosomes align midway between the poles

c.       Anaphase I

Mics. Shorten and move towards spindle pole, pulling chromosomes apart.

d.      Telophase I

One of each type of chromosome has arrived at spindle poles, cytoplasm divides, forming two haploid cells

e.       Prophase II

New bipolar spindle forms in each haploid cell, centrioles move to opp. Sides of cell, chromatids become tethered.

f.       Metaphase II

Chromosomes line up at poles. Same process as Metaphase I.

g.      Anaphase II

Sister chromatids break apart, mics. Move chromosomes toward spindle poles.

h.      Telophase II

4 nuclei form as new nuclear envelope encloses each cluster of chromosomes. Daughter cells are haploid.

10.4 Outline

I. How meiosis introduces variation in Traits

A. Crossing over in Prophase

            1. sister chromatids become stuck at certain point of chromosome

            2. when Dna strands break, segments break off and fuse with opp chromatid. This is called gene swapping, creating vast variety in genes.

B. Metaphase I Alignments

            1. random tethering of duplicated chromosomes to microtubules

                        a. more variation!

            2. either chromosome partner can endu up at either spindle pole

            3.  This means that there are 8,388,608 possible combinations of maternal and paternal chromosomes in human sperm and egg cells.

Differences between Mitosis and Meiosis

            Meiosis                                                            Mitosis

-          Purpose: reproduction                                     Purpose: growth and repair

-          Occurs only in reproductive cells                    occurs in all somatic cells

-          Results in 4 haploid gametes                          results in 2 Diploid cells

-          Results in genetically variable cells                 results in genetically identical cells

-          2 rounds of division                                        1 round of division

-          Results in cells w/ 23 chromosomes                results in cells w/ 46 chromosomes