Cellular Reproduction Unit 4 (Ch.9, 10.1)

TYPES OF REPRODUCTION AsexualAsexual –Relies on MITOSIS –All of the parent’s DNA goes to the offspring –Bacteria reproduce through binary fission SexualSexual –Relies on MEIOSIS –Used to create sex cells

TYPES OF CELLS Body CellsBody Cells –Includes all cells that are not sex cells i.e. skin, liver, muscle, etc…i.e. skin, liver, muscle, etc… –Also called somatic cells (soma- means “body”) –Made by MITOSIS –Contain 2 copies of each chromosome Called homologous chromosomesCalled homologous chromosomes Have a diploid # (2n)Have a diploid # (2n) –Ex. Humans = 46

TYPES OF CELLS Sex CellsSex Cells –Include egg cells and sperm cells –Also called gametes –Made by MEIOSIS –Contain 1 copies of each chromosome Have a haploid # (n)Have a haploid # (n) –Ex. Humans = 23

Chromosome Numbers Sperm (haploid # of 23) Egg Zygote (diploid # of 46) Fertilization

Meiosis Produces Sex CellsProduces Sex Cells Reduction divisionReduction division –Starts with 1 diploid cell and ends up with 4 haploid cells Occurs in TWO stepsOccurs in TWO steps –Meiosis I –Meiosis II

Interphase Chromosomes replicateChromosomes replicate Chromatin condensesChromatin condenses Interphase

Homologous Chromosomes One of two paired chromosomes, one from each parentOne of two paired chromosomes, one from each parent Same lengthSame length Same centromere positionSame centromere position Carry genes that control the same inherited traitsCarry genes that control the same inherited traits

Homologous Chromosomes

Prophase I Pairing of homologous chromosomes occursPairing of homologous chromosomes occurs –Each chromosome consists of two sister chromatids The nuclear envelope breaks downThe nuclear envelope breaks down Spindles formSpindles form Prophase I

Crossing Over The exchange of material between homologuesThe exchange of material between homologues –Occurs during Prophase I –Tetrads are formed and DNA is exchanged –Produces chromosomes that contain genes from both parents… GENETIC DIVERSITY

Metaphase I Chromosome centromeres attach to spindle fibersChromosome centromeres attach to spindle fibers Homologous chromosomes (tetrads) line up at the equatorHomologous chromosomes (tetrads) line up at the equator

Independent Assortment The random distribution of genes located on different chromosomes.The random distribution of genes located on different chromosomes. Since each homologous pair assorts independently from all others, the process produces 2 n possible combinations of maternal and paternal chromosomes in gametes (where n is the haploid number)Since each homologous pair assorts independently from all others, the process produces 2 n possible combinations of maternal and paternal chromosomes in gametes (where n is the haploid number) In humans, the possible combinations would be 2 23, or eight million – there are eight million possible assortments of chromosomes from the parentsIn humans, the possible combinations would be 2 23, or eight million – there are eight million possible assortments of chromosomes from the parents

Independent Assortment

Anaphase I Homologous chromosomes separate and spindle fibers move them towards opposite poles of the cellHomologous chromosomes separate and spindle fibers move them towards opposite poles of the cell Anaphase I

Telophase I Telophase I & Cytokinesis Telophase I Spindles break downSpindles break down Chromosomes uncoil to form two nucleiChromosomes uncoil to form two nucleiCytokinesis The cell divides into two new daughter cellsThe cell divides into two new daughter cells  Each pole now has a haploid set of chromosomes that are still composed of two sister chromatids attached at a centromere

MEIOSIS II This second division separates sister chromatids of each chromosome (virtually identical to Mitosis)This second division separates sister chromatids of each chromosome (virtually identical to Mitosis)

Prophase II Spindle apparatus forms and chromosomes condenseSpindle apparatus forms and chromosomes condense Prophase II

Metaphase II A haploid number of chromosomes align along the metaphase plateA haploid number of chromosomes align along the metaphase plate Metaphase II

Anaphase II Chromosomes are pulled apart producing sister chromatids.Chromosomes are pulled apart producing sister chromatids. –Each chromatid is pulled (by the spindles) towards the opposite poles of the cell Anaphase II

Telophase II & Cytokinesis Telophase II Chromatids reach the polesChromatids reach the poles Nuclear membranes and nuclei reformNuclear membranes and nuclei reformCytokinesis Results in four haploid cells, each with n number of chromosomes.Results in four haploid cells, each with n number of chromosomes. Telophase IICytokinesis

Gamete Development in Males “SPERMATOGENESIS”“SPERMATOGENESIS” Meiosis occurs in testes at puberty and then occurs as neededMeiosis occurs in testes at puberty and then occurs as needed 1 spermatocyte = 4 sperm cells1 spermatocyte = 4 sperm cells

Gamete Development in Females “OOGENESIS”“OOGENESIS” Meiosis occurs in the ovaries before birthMeiosis occurs in the ovaries before birth 1 oocyte = 1 egg & 3 polar bodies1 oocyte = 1 egg & 3 polar bodies

HUMAN LIFE CYCLE Uses both meiosis & mitosis