Chapter 13: Meiosis
Chapter 13: Meiosis BIOl 1020-003
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This 4 page Class Notes was uploaded by Crystal Boutwell on Sunday October 25, 2015. The Class Notes belongs to BIOl 1020-003 at Auburn University taught by Dr. Zhong in Fall 2015. Since its upload, it has received 23 views. For similar materials see Principles of Biology in Biology at Auburn University.
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Date Created: 10/25/15
CHAPTER 13 MEIOSIS Compiled by Crystal Boutwell Introduction A the transfer of traits from one generation to the next also called inheritance B the differences in heredity C the scientific study of heredity and variation Offspring inherit chromosomes from parents thus acquiring their genes A hereditary units that are passed on to children from their parents i The inherited information eye color etc is passed on to the offspring through the form of each gene s specific sequence of DNA nucleotides Different sequences different genes B reproductive cells in animals and plants the vehicles by which genes are transmitted from the parents to the offspring i During fertilization the egg and sperm merge passing on genes from each parent C Composition of a chromosome one single long DNA molecule coiled with proteins i Can carry several hundred to a few thousand genes the specific location on a chromosome where a gene resides E Only organisms that reproduce asexually have offspring that are exact genetic copies of themselves F Asexual reproduction occurs whenever a single parent is the sole parent and passes all of its genes to its offspring without the fusion of gametes i s groups of genetically identical individuals ii Genetic differences arise from mutations changes in DNA G Sexual Reproduction 2 parents the offspring s genes are a combination of the parents genes The sexual life cycle Fertilization and Meiosis A the sequence of stages from generation to generation in the reproductive history of an organism starting at conception and ending at the production of its own offspring B Human somatic cells have 46 chromosomes 2 chromosomes23 types C an ordered display of chromosomes in their pairs D The two chromosomes that pair have the same length centromere position and staining pattern i Both carry genes controlling the same inherited characters eye color hair color etc ii Exception X and Y chromosomes 3 Sex chromosomes all other chromosomes are called autosomes iii We inherit one chromosome from each pair from each parent 23 chromosomes from mom 23 from dad E of chromosomes in a single set n i Any cell with a two chromosome set is called a diploid cell 2n 1 Human somatic cells 2n 46 N number of pairs 46 total number of chromosomes ii Gametes contain a single set of chromosomes haploid cells n 1 Humans have 23 chromosomes in a haploid cell n23 22 autosomes and 1 sex chromosome a An unfertilized egg contains an X but sperm may contain an X or a Y which is why the guy determines the sex of the baby F the union of gametes into a zygote fertilized diploid egg i Mitosis of the zygote produces all somatic cells of the body G gamete formation in sexually reproducing organs i 2n after fertilization until meiosis ii N after meiosis until fertilization H Three Types of Life Cycles i Humans and most animals 1 Gametes are only haploid cells 2 Meiosis occurs in germ cells 3 Gametes undergo no further cell division prior to fertilization 4 After fertilization the diploid zygote divides by mitosis creating a multicellular organism ii Plants and some algae 1 Alternation of generation 2 Both diploid and haploid stages that are multicellular 3 Begins as a sporophyte diploid and becomes a spore which do not fuse with another cell but divide mitocally into a multicellular haploid stage gametophyte which produces gametes via mitosis iii Fungi and protists 1 Gametes fuse to forma diploid zygote the only diploid part of this process 2 Meiosis occurs without a multicellular diploid offspring developing 3 Haploid cells divide by means of mitosis into unicellular descendants or haploid multicellular adult organisms IV Meiosis process duplication of chromosomes reduction of number of chromosomes from diploid to haploid Followed by two divisions resulting in 4 daughter cells A nterphase i Pair of homologous chromosomes in diploid parent cell 9 pair of duplicated homologous chromosomes each with a sister chromatid B Meiosis I Prophase I Metaphase I Anaphase I Telophase I i Reductional division ii Homologous chromosomes pair up during Prophase I Crossing over occurs iii Homologous chromosomes line up at the equatorial plate randomly during Metaphase I iv Homologous chromosomes separate during Anaphase I v Produces two haploid cells with duplicated chromosomes C Meiosis II Prophase II Metaphase II Anaphase II Telophase II i Equational division ii Sister chromatids separate during Anaphase II iii Produces four haploid cells with unduplicated chromosomes different versions of genes on homologs at corresponding loci E the combination of crossing over in prophase I and sister chromatid cohesion hold homologs together as the spindle forms F a zipperlike structure that holds one homolog tightly to another i Associations paternal chromatid crosses over maternal chromatid G Comparison of Mitosis and Meiosis 1 Reduces the number of chromosome sets from 2 to 1 2 Produces daughter cells genetically different from the parent cells a Crossing over mixes genes between the chromosomes b The order in which homologous chromosomes line up at the metaphase plate is random metaphase I c The direction in which sister chromatids are pulled in anaphase II is random 1 Conserves the number of chromosomes sets 2 Produces daughter cells identical to parent cells i Synapsis and crossing over prophase I duplicated homologs pair up and cross over sharing genetic information ii Homolog pairs at metaphase plate metaphase I positioned in plate as pairs of homologs not individual chromosomes iii Separation of homologs Anaphase I sister chromatids remain intact while homologs move toward opposite poles iv These are all reasons for mm V I Maw 00 I 0 0 0 0
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