2 GametesGametes are reproductive cells (eggs and sperm) that contain half the complement of chromosomes found in somatic cellsthe gametes fuse to form a new cell called a zygote, which contains two complete copies of each chromosomethe fusion of gametes is called fertilization, or syngamyegg + sperm = Zygote
3 Haploid Cell vs. Diploid Cell Typically, each cell of your body has 46 chromosomes..23 from each parentSo, you have what we call a Diploid value of 46Or, referred to as 2N = 46Your gametes, however, have 1N values1N = 23….This is a Haploid conditionAll your normal body cells are diploid, only your gametes are haploidTHIS IS TRUE FOR MOST ORGANISMS!!!!!!Sex Cells
4 Chromosome NumberEvery organisms inherits chromosomes from their parents.Asexually reproducing organisms pass on their full set of chromosome creating offspring that are essentially clones of themselvesSexually reproducing organisms pass on half of their chromosomes through their sex cells. The offspring created inherits half of its chromosomes from each parent.
5 Human Life Cycle Gamete- egg and sperm Zygote- cell produced when egg and sperm fuseFertilization/ syngamy- fusion of gametes
6 TraitsInheritable traits are carried on factors called genes and are passed down from generation to generation.Genes are located on DNA within the nucleus of the cell.There are two alleles for every gene. One allele is inherited from each parentAlleles are alternate versions of a geneThe process by which chromosomes are separated in the production of sex cells is known as Meiosis.
7 Homologous Chromosomes Homologous Chromosomes- chromosomes that carry the alleles for the same gene.Diploid Cells- (2N) “Two sets”; have both sets of homologous chromosomes (All body cells are diploid)Haploid Cells- (1N) “one set”; has a single set of genes. (All sex cells are haploid)
8 MeiosisMeiosis- is the process by which the homologous chromosomes are separated in a diploid cell to produce a haploid cellMeiosis involves two divisions, meiosis I and meiosis IImeiosis I separates the homologues in a homologous pairmeiosis II separates the replicate sister chromatids
9 Meiosis IMeiosis I is traditionally divided into four sequential stagesProphase IHomologous chromsomes pair up and exchange segmentsMetaphase IThe paired homologous chromosomes align on a central planeAnaphase IHomologues are pulled apart and move to opposite poles of the cellTelophase IIndividual replicated chromosomes gather at each of the two poles
10 Prophase IPrior to the start of Meiosis, chromosomes are replicated during Interphase.During Prophase I homologous chromosomes pair up to form a tetrad (there are 4 chromatids in a tetrad)Crossing over may occur when the tetrads exchange a portion of the chromatidsDuring crossing-over chromatids break and may be reattached to a different homologous chromosome.Human female eggs remain in Meiosis I until puberty… years
11 Meiosis I: Metaphase IEach homologous set of chromosomes line up along cell centerOrientation on the metaphase plate is random…with either parental homologue on a side. This means that there is a chance for the daughter cells to get either the mother's or father's homologue for each chromosome.
12 Metaphase IDuring metaphase I, the orientation of the homologous chromosome pairs is a matter of chanceeach possible orientation of which homologue in a homologous pair faces which pole results in gametes with different combinations of parental chromosomesthis process is called independent assortment
13 Meiosis I: Anaphase I Homologs are pulled apart to opposite poles Chromosomes, each with two chromatids, move to separate poles.Each of the daughter cells is now haploid (23 chromosomes), but each chromosome has two chromatids.
14 Meiosis I: Telophase I Homologous chromosomes have fully separated Results in a Haploid (1N) set of chromosomes at each poleNuclear envelopes may reform, or the cell may quickly start meiosis 2.
16 Meiois II Meiosis II is also divided into four stages Prophase II new spindle forms to attach to chromosome clustersMetaphase IIspindle fibers bind to both sides of the centromere and individual chromosomes align along a central planeAnaphase IIsister chromatids move to opposite polesTelophase IIthe nuclear envelope is reformed around each of the four sets of daughter chromosomes
20 Why Sex??Sexual reproduction has an enormous impact on how species evolve because it rapidly generates new genetic combinationsThree mechanisms help produce this varietyIndependent assortmentCrossing overRandom fertilization
21 GametogenesisGametogenesis the process of forming gametes (haploid, 1n) from diploid cells (somatic cells) of the germ line.Spermatogenesis is the process of forming sperm cells by meiosis. In spermatogenesis all 4 meiotic products develop into gametes and human males produce 200,000,000 sperm per dayOogenesis is the process of forming an ovum (egg) by meiosis in specialized gonads known as ovaries. Human females female produce one egg (usually) each menstrual cycle