Unformatted text preview:

Chapter 13 (Meiosis and Cell Life Cycles):Heredity- the transformation of traits from one generation to the nextGenetics- scientific study of heredity and heredity variation13.1:Genes- hereditary units that are given from parents to offspringGenes translated into features/traitsGametes- reproductive cellsMale- sperm cells, female-eggsMajority of DNA in a Eukaryote is packaged into chromosomes in the nucleusLocus- a genes specific location along the length of a chromosomeAsexual Reproduction- a single individual is the sole parent and passes copies of all its genes to its offspring without the fusion of gametesOffspring are clonesClone- a group of genetically identical individualsSexual reproduction- two parents give rise to offspring that have unique combinations of genes inherited from the two parents13.2:Life cycle- the generation to generation sequence of stages in the reproductive history of an organism, from conception to production of its own offspringKarotype- a display of condensed chromosomes arranged in pairsHomologous chromosomes have the same length, centromere position, and staining patternSex chromosomes- X and Y chromosomes (not homologous)Autosomes- the other chromosomesDiploid cells-Any cell with two chromosome sets, abbreviated 2n.For humans, diploid number is 46 (2n=46)Haploid cells- single sets of chromosomes as found in gametes, abbreviated n.For humans, haploid number is 23 (n=23)The set of 23 consists of 22 autosomes plus a single sex chromosomeFertilization- union of gametes culminating in fusion of their nucleiZygote- resulting fertilized eggDiploid because it contains two haploid sets of chromosomes bearing genes representing the maternal and paternal family linesMitosis of the zygote and its descendent cells generates the somatic cells in the bodyGametes are the cells not produced by mitosisDevelop from specialized cells called germ cells in the gonads (ovaries in females and testes in males)Three types of life cycles (alternation between meiosis and fertilization)HumansGametes are only haploid cellsMeiosis occurs in germ cells during production of gametes. Gametes undergo no further cell division prior to fertilizationAfter fertilization, diploid zygote divides by mitosis to produce a multicellular organism that is diploidAlternation of generations (plants and some algae)Includes both diplod and haploid stages that are multicellularSporophyte-multicellular diploid stageSpores- haploid cells that are products of meiosis in the sporophyteThe haploid spore does not fuse with another cell. It instead divides mitotically to generate a multicellular haploid stage called the gameophyte.Cells of gameophyte give rise to gametes by mitosis. Fusion of two haploid gametes at fertilization results in a diploid zygote, which develops into the next sporophyte generationSummary: Sporophyte generation produces a gameophyte as its offspring, and the gameophyte generation produces the next sporophyte generation.Life cycle of Fungi and ProtistsAfter gametes fuse and form a diploid zygote, meiosis occurs without a multicellular offspring forming.Meiosis does not produce gametes, but instead produces haploid cellsThese haploid cells divide by mitosis and give rise to either unicellular descendents or a haploid multicellular organism.The haploid organism carries out further mitosis to produce the cells that develop into gametesOnly diploid stage found in these species is the single celled zygoteEither haploid or diploid cells can divide by mitosis depending on the cell cycle.Only diploid cells can undergo meiosis because haploid cells have a single set of chromosomes that cannot be further reduced13.3: Meiosis reduced the number of chromosomes sets from diploid to haploidMeiosis is preceded by duplication of chromosomesSingle duplication followed by two consecutive cell divisions (meiosis I and meiosis II)The two chromosomes of a homologous pair are individual chromosomes that were inherited from different parentsHomologs may have different alleles, versions of genes, at corresponding lociMeiosis in an Animal Cell:Mitosis v MeiosisAll events unique to meiosis occur in meiosis ISynapsis and Crossing Over- Duplicated chromosomes pair up during prophase I and the synaptonemal complex forms to hold them in synapsis. Crossing over occurs at chiasmataHomologous pairs at the metaphase plate- Chromosomes are positioned at the metaphase plate as homologs insteads of individual chromosomes like in mitosisSeparation of homologs- During anaphase I, the duplicated chromosomes of each homologous pair move toward opposite poles, but sister chromatids remain attached. In anaphase of mitosis, sister chromatids separateMore info on Meiosis:Sister chromatid cohesion in meiosis is released in two steps: one at anaphase I and the second at anaphase IIThe combination of crossing over and sister chromatid cohesion result in the formation of chiasma. Chiasma hold homologs together as the spindle forms for the first meiotic divisonAt onset of anaphase I, the release of cohesion along sister chromatid arms allows homologs to separateAt anaphase II, the release of sister chromatid cohesion at the centromeres allows sister chromatids to separateMeiosis I is called reductional division because it halves the number of chromosome sets per cell from 2 to 1.Meiosis II is called the equational division because the sister chromatids separate to form haploid cells13.4: Genetic Variation produced in sexual life cycles contributes to evolution.Mutations are the original source of genetic diversityResult in the creation of different allelesIndependent Assortment of Chromosomes occurring at metaphase ICrossing Over resulting in the production of recombinant chromosomesRecombinant chromosomes- individual chromosomes that carry genes (DNA) derived from 2 different parentsOn average, one to three crossovers occur per chromosome pair depending on size of chromosome and position of centromeresBio 1107 Chapter 13 03/26/2013Chapter 13 (Meiosis and Cell Life Cycles):Heredity- the transformation of traits from one generation to the nextGenetics- scientific study of heredity and heredity variation 13.1:Genes- hereditary units that are given from parents to offspringGenes translated into features/traitsGametes- reproductive cellsMale- sperm cells, female-eggsMajority of DNA in a Eukaryote is packaged into chromosomes in the nucleusLocus- a genes specific location along the length of a chromosomeAsexual Reproduction- a


View Full Document

UGA BIOL 1107 - Chapter 13

Download Chapter 13
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Chapter 13 and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Chapter 13 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?