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Bio Notes 3-7-2016

by: Crystal Florman

Bio Notes 3-7-2016 BIOL 1014

Crystal Florman
GPA 3.64

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Meiosis II and sources of genetic variation
Life: Continuity and Change
Dr. Kurt Pontasch
Class Notes
Meiosis II, sexual variance, source of variation
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This 2 page Class Notes was uploaded by Crystal Florman on Tuesday March 8, 2016. The Class Notes belongs to BIOL 1014 at University of Northern Iowa taught by Dr. Kurt Pontasch in Spring 2016. Since its upload, it has received 51 views. For similar materials see Life: Continuity and Change in Biology at University of Northern Iowa.


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Date Created: 03/08/16
Life: Continuity and Change Lecture Notes 3-7-2016 Meiosis II  Four stages o Prophase II- nuclear membrane disintegrates and spindle fibers form as centrioles move to the poles o Metaphase II- chromosomes attach to spindle fibers at centromeres and move to the equatorial plain o Anaphase II- chromosomes split at the centromere and the chromatids move to the poles o Telophase II- nuclear membrane reforms and chromosomes uncoil and become long thin threads  You end up with one of the four chromatids form each homologous pair in the gametes  After telophase II the four cells that have been produced in meiosis differentiate into gametes o In females- three of the four cells created will disintegrate o In males- all will be used as gametes Source of Variation  Sexual Reproduction results in a variety of offspring- with the possible exception of identical twins, every human that has ever been born is genetically unique o Five factors that influence the genetic variation in offspring  Mutations- previously discussed (2-29-2016)  Crossing over- exchange of part of the chromatid from one homologous chromosome with the equivalent part of the chromatid on the other homologous chromosome  Occurs during prophase I when homologous chromosomes are synapsed  The bonds between the sugar and the phosphate are broken at the same place on both chromatids  Creates four different gamete rather than two pairs of identical gametes  Hundreds/ thousands of genes located at specific places on the chromosome  Locus- specific place a gene is located on the chromosome  Can happen anywhere on the chromosome  Can occur more than once on the same pair  Segregation- involves only 1 pair of homologous chromosomes  After crossing over has occurred- segregation occurs  Movement of the HC to the poles during anaphase I  Pairs line up randomly during metaphase I- segregation results in an equal chance of genes form HC to be passed on to the daughter cells  Independent Assortment- involves all pairs of homologous chromosomes  Two pairs of HC- assume that one pair of HC has the gene for normal insulin and the other has the gene for diabetes  Another pair has the gene for five fingers and six fingers  The pole to which chromosome moves to is a chance event- with two HC pairs there are four kinds of gametes o Insulin- 5 fingers o Insulin- 6 fingers o Diabetes- 5 fingers o Diabetes- 6 fingers  With three pairs there are 8 kinds of gametes- humans have 23 pairs so there are 8,388,608 kinds of gametes  Fertilization- because of the large number of kinds of gametes- a larger number of types of offspring can be produced  For all practical purposes the number of kinds of offspring is infinite Sex Determination  Sexual characteristics are determined by genes like other characteristics  In many organisms the sex is determined by genes on the sex chromosomes (X and Y)- other chromosomes are called autosomes  In mammals the genes that determine maleness are on the Y chromosome o The Y chromosome acts as if it is homologous with the X chromosome- they line up and split during anaphase I o Males- XY o Females- XX


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