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TAMU BIOL 111 - Ch 13 Blueprint
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Rebecca Davenport BIOL 140611/14/16Ch 13 blueprint1. Meiosisi. Meiosis reduces the number of chromosomes by half (2n to n)ii. Form of sexual reproduction.iii. Egg + Sperm >>undergoes Fertilization>> to form a Zygote >>Which undergoes mitosis>> to form multicellular. Germ cells circle back to gametes undergoing meiosis. iv. Only diploid cells can undergo meiosisv. Preceded by the replication of chromosomesvi. Meiosis takes place in two consecutive cell divisions, called meiosis I and meiosisIIvii. Two rounds of Meiosis results in four haploid daughter cellsviii. Genetically unique daughter cellsix.1. Two phases of Meiosis:a. Meiosis 1- separates homologous (mom set and dad set) chromosomes. i. Prophase I1. Each chromosome pairs with its homolog and crossing over occurs (sections of each chromatin swap)2. X-shaped regions called chiasmata are sitesof crossoverii. Metaphase I1. Pairs of homologs line up at the metaphase plate, with one chromosome facing each pole2. Microtubules are attached to the kinetochoreiii. Anaphase I1. Pairs of homologous chromosomes separate and move to opposite poles2. Sister chromatids remain attached at the centromere and move as one unit toward the poleiv. Telophase I and Cytokinesis1. Nuclear envelope reforms, spindle dissipates. 2. Each half of the cell has a haploid set of chromosomes; each chromosome still consists of two sister chromatids3. Cytokinesis usually occurs simultaneously, forming two haploid daughter cellsv.b. Meiosis 2- separates sister chromatids; Mom has sister chromatids and dad sister chromatids, when one of each is paired they are called non-sister chromatids.i. Prophase II1. In prophase II, a spindle apparatus forms2. In late prophase II, chromosomes (each still composed of two chromatids) move toward the metaphase plateii. Metaphase II1. Sister chromatids arranged at the metaphase plate2. Sister chromatids of each chromosome are no longer genetically identical due to crossing over (Meiosis I)3. Kinetochores of sister chromatids attach to microtubules extending from opposite polesiii. Anaphase II1. Sister chromatids separate2. Sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite polesiv. Telophase II and Cytokinesis1. Chromosomes arrive at opposite poles2. Nuclei form, and the chromosomes begin decondensing3. At the end of meiosis, there are four daughter cells, each with a haploid set of unreplicated chromosomes4. Each daughter cell is genetically distinct from the others and from the parent cell.c.x. Crossing over and Synapsis during Prophase I:1. Sister chromatids held together by cohesins2. Nonsister chromatids are broken at corresponding positions3. A zipper-like structure, the synaptonemal complex, holds the homologs together 4. DNA breaks are repaired, joining DNA from one nonsister chromatid to the corresponding segment of another.5.6.b. Inheritance of genes: i. Heredity is the transmission of traits from one generation to the nextii. Genetics is the scientific study of heredity and variationiii. Genes are the units of heredity and are made up of segments of DNAiv. Genes are passed to the next generation via reproductive cells called gametes (sperm and eggs) v. A gene’s specific position along a chromosome is called the locusc. Comparison of Asexual and Sexual reproduction:i. Asexual reproduction: a single individual passes all of its genes to its offspring without the fusion of gametes – produces a clone.ii. Sexual reproduction: two parents give rise to offspring that have unique combinations of genes inherited from the two parents.d. Sets of chromosomes in human cells:i. A karyotype is an ordered display of the pairs of chromosomes from a cell ii. The two chromosomes in each pair are called homologous chromosomesiii. Number of chromosomes in one set is “n”1. Haploid = n2. Diploid = 2niv. Duplicating chromosomes-ChiasmataCrossover1.e. Origins of genetic variation among offspring:i. The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generationii. Three mechanisms contribute to genetic variation-1. Independent assortment of chromosomes:a. Homologous pairs of chromosomes orient randomly at metaphase 1 of meiosis.b. In independent assortment, each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs.c.2. Crossing over:a. Crossing over produces recombinant chromosomes, which combine DNA inherited from each parentb. Crossing over contributes to genetic variation by combining DNAfrom two parents into a single chromosomec. In humans an average of one to three crossover events occurs per chromosome.d.3. Random fertilization:a. Random fertilization adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg).b. The fusion of two gametes (each with 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about 70 trillion diploid combinations.f. Fertilization and zygotes:i. Fertilization is the union of gametes (the sperm and the egg)ii. The fertilized egg is called a zygote and has one set of chromosomes from each parent iii. The zygote produces somatic cells by mitosis and develops into an adultiv. Meiosis of germ cells results in one set of chromosomes in each gametev.2. Comparison of Mitosis and Meiosis:a. Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cellb. Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cellHaploid (n)Diploid


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TAMU BIOL 111 - Ch 13 Blueprint

Type: Chapter Summary
Pages: 8
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