Biosciences I BIO 1404
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Mr. Uriel Harvey
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This 2 page Class Notes was uploaded by Mr. Uriel Harvey on Thursday October 29, 2015. The Class Notes belongs to BIO 1404 at University of Texas at San Antonio taught by David Jaffe in Fall. Since its upload, it has received 24 views. For similar materials see /class/231362/bio-1404-university-of-texas-at-san-antonio in Biology at University of Texas at San Antonio.
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Date Created: 10/29/15
Chapter 13 meiosis Hereditary transmission of traits by inheritance Genetics study of heredity and hereditary variation Genes coded information in the form of hereditary unit Gametes vehicles that transmit genes from one generation to the next Somatic cells all cells of the body except the gametes and their precursors o Humans have 46 chromosomes Locus gene s speci c location along the length of a chromosome Aesexual reproduction dingle individual is the sole parent and passes copies of all its genes to its offspring without the fusion of gametes 0 Clone group of genetically identical individuals Sexual reproduction two parents give rise to offspring that have unique combinations of genes inherited from the two parents Karyotype the resulting display of ordered chromosomes 1 39 39 two 39 r 39 a pair Sex chromosome X Y Autosomes the other chromosomes Diploid cell any cell with two chromosome set 0 2n 0 Somatic cells Haploid cell a cell that contains a single set of chromosomes 0 N o Gametes Fertilization union of gametes o Zygote the resulting egg I Diploid Alteration of generations 0 Both diploid and haploid stages that are multicellular I Plants and some species of algae I Sporophyte mutlicellualr diploid stage 0 Meiosis produces haploid cells called spores o Gametophyte mitotic stage where the haploid spores give rise to gametes Meiosis o Divided into 2 parts 0 Begins with interphase I Pair of homologous chromosomes in a diploid parent cells becomes a 1 1I39 I o Meiosis l I Homologous chromosomes separate and become two haploid cells with duplicated chromosomes 0 Meiosis 2 I Duplicated chromosomes separate into two and become 4 unduplicated haploid chromosome Meiosis l o Prophase l chromosomes begin to condense and homolog loosely pair along their lengths aligned gene by gene I Paired homologs become physically connected to each other along their lengths by a zipperlike protein structure the synaptonemal complex this state is called synapsis Crossing over a genetic rearrangement between nonsister chromatids involving the exchange of corresponding segments of DNA molecules beings during pairing and synaptonemal complex formation and it completed while homologs are in synapsis Each homologous pair has one or more X shaped regions called chaismata This exists at the point where a crossover has occurred It appears as a cross because sister chromatid cohesion still holds the two original sister chromatids together even in regions beyond the crossover point where one chromatid is now part of the other homolog Metaphase 1 pairs of homologous chromosomes are now alranged at the metaphase plate with one chromosome in each pair facing each pole I Both chromatids of one homolog are attached to kintechore microtubules from one pole those of the other homolog are attached to microtubules from the opposite pole Anaphase l breakdown of proteins responsible for sister chromatid cohesion long chromatid arms allow homologs to separate I The homologs move toward opposite poles guided by the spindle apparatus I Sister chromatid cohesion persists at the centromere causing chromatids to move as a unit toward the same pole Telophase 1 each half of the cell has a complete haploid set of duplicated 39 Each 39 is r J to two sister chromatids one or both chromatids include regions of nonsister chromatid DNA Cytokinesis Usually occurs simultaneously with telophase l forming two haploid daughter cells Prophase II a spindle apparatus forms I In late prophase 11 chromosomes each still composed to two chromatids associated at the centromere move toward to metaphase 11 plate Metaphase 11 chromosomes are positioned at the metaphase palte as in mitosis I Because crossing over in meiosis I the two sister chromatids of each chromosome are not genetically identical I The kinetochores of sister chromatids are attached to microtubules extending from opposite poles Anaphase II breakdown of proteins holding the sister chromatids together at the centromere allows the chromatids to separate The chromatids move toward opposite poles as individual chromosomes Telophase II nuclei form the chromosomes begin decondensing Cytokinesis II The meiotic division of one parent cell produces four daughter cells each with a haploid set of unduplicated chromosomes I The four daughter cells are genetically distinct from one another and from the parent cell Genetic variation by meiosis O O O O O O O OO O
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