Problem of the day: Cancer is many diseases that all have the same root problem. Chemotherapy is aimed at this problem. What exactly does chemotherapy attempt to do?

Essential Knowledge: In eukaryotes, heritable information is passed to the next generation via processes than include the cell cycle and mitosis or meiosis plus fertilization. Meiosis and Sexual Life Cycles

You Must Know 4 The differences between asexual and sexual reproduction 4 The role of meiosis and fertilization in sexually reproducing organisms 4 The importance of homologous chromosomes to meiosis 4 How the chromosome number is reduced from diploid to haploid through the stages of meiosis 4 3 important differences between mitosis and meiosis 4 The importance of crossing over, independent assortment, and random fertilization to increasing genetic variability.

Terms to Know 4 heredity-transmission of traits from one generation to the next 4 genetics-study of heredity and hereditary variation 4 genes-segments of DNA consisting of specific sequences of nucleotides; most program for enzymes and other proteins; found on chromosomes; acquired from parents 4 locus-the location of a specific gene on a chromosome 4 karyotype-ordered display of chromosomes 4 Somatic cells-cells in the body that are not gametes 4 gametes- sex cells; egg and sperm 4 meiosis- cell division to produce haploid gametes 4 fertilization- male and female gametes unite to form a zygote 4 Autosomes-non-sex chromosomes (humans 1-22)

Asexual Reproduction Binary Fission is a form of asexual reproduction found in prokaryotic organisms. Eukaryotes may use mitosis to reproduce. Both forms of asexual reproduction result in clones- gentically identical organisms/cells

Sexual Reproduction in Eukaryotes Meiosis: 4 Used to form gametes (egg and sperm) 4 Reduces the number of chromosome sets from diploid to haploid (Why?) 4 Final result is 4 daughter cells, each with half as many chromosomes as the parent cell 4 Fertilization and meiosis alternate in sexual life cycles Life cycle: generation to generation sequence of stages in the reproductive history of an organism

Mitosis vs. Meiosis Mitosis 4 Produces diploid cells 4 Used to grow and repair 4 Daughter cells are genetically identical 4 Meiosis 4 Produces haploid cells 4 Used to produce gametes 4 Daughter cells are NOT genetically identical 4 Crossing over occurs in prophase

Alternative life cycles 4 Fungi/some algae meiosis produces 1N cells that divide by mitosis to produce 1N adults (gametes by mitosis) (the only diploid stage is the zygote 4 Plants/some algae Alternation of generations: 2N sporophyte, by meiosis, produces 1N spores; spore divides by mitosis to generate a 1N gametophyte; gametes then made by mitosis which then fertilize into 2N sporophyte

Summary of Sexual Life Cycles 4 Animal-gametes are the only haploid cells 4 Fungi-zygote is the only diploid cell 4 Plants-alternate between a multicellular haploid (pollen, ovules) and diploid stage

Meiosis Terms 4 Homologues: members of a pair of chromosomes; one from each parent; contain same set of genes 4 Synapsis: when homologues come together, line up and lay alongside each other as bivalents; form tetrads 4 Crossing over: when homologues exchange equal amounts of genetic material; sister chromatids are no longer identical after this 4 Chiasmata: places where crossing over occurs; x- shaped region

Role of Meiosis 4 Reduction division so each gamete receives one complete haploid set of chromosomes 4 Fertilization will result in a diploid zygote 4 Genetic diversity is achieved 4 One member of each pair of homologues is from the maternal and one member is from the paternal parent. Karyotype homologues

Homologues or Homologous Chromosomes 4 Similar in length and centromere position 4 Have the same staining pattern 4 One member of each pair is inherited from each parent 4 X and Y are NOT homologous

Meiosis 4 Solves the problem created by sexual reproduction 4 2n  1n 4 4 cells 4 Gametes are not clones 4 Two stages meiosis I and meiosis II

Meiosis 4 Preceded by chromosome replication, but is followed by 2 cell divisions (Meiosis I & Meiosis II) 4 4 daughter cells; 1/2 chromosome number (1N); variation

What is happening in Meiosis I? 4 Synapsis-tetrad formation 4 Crossing over-exchange of genetic information 4 Homologous PAIRS line up 4 Homologues separate 4 Chromosome number is halved

Meiosis I: Reduction Division 4 Interphase I-DNA replication 4 Prophase I-synapsis occurs; tetrad forms; crossing-over occurs 4 Metaphase I-paired homologues (tetrads) are positioned at the metaphase plate, (rather than individual replicated chromosomes as in mitosis) 4 Anaphase I-sister chromatids remain attached, but homologues separate (in mitosis chromatids separate) 4 Telophase I-occurs only in some species

What happens in Meiosis II? 4 Much like mitosis 4 Sister chromatids of homologues separate

Meiosis II-resembles mitosis 4 Interphase II- No S phase 4 Prophase II 4 Metaphase II- chromatids separate 4 Anaphase II 4 Telophase II-four haploid cells

Meiosis vs. mitosis

Origins of Genetic Variation, IGenetic Variation 4 Independent assortment: homologous pairs of chromosomes position and orient randomly (metaphase I) and nonidentical sister chromatids during meiosis II 4 Combinations possible: 2 n ; with n the haploid number of the organism 4 e.g. humans 2 23 =8,388,608 possible combinations

Origins of Genetic Variation, II 4 Crossing over (prophase I): the reciprocal exchange of genetic material between nonsister chromatids during synapsis of meiosis I (recombinant chromosomes) 4 Random fertilization: 1 sperm (1 of 8 million possible chromosome combinations) x 1 ovum (1 of 8 million different possibilities) = 64 trillion diploid combinations!; crossing over adds even more variations

Mutations 4 the original source of genetic variation 4 changes in an organism’s DNA creates a new version of a gene 4 most are harmful, but a few may be helpful to the survival of a species 4 Changes in chromosome number often result in new phenotypes 4 Changes in chromosome number in humans results in genetic disorders, like Trisomy 21

Darwin and Mendel 4 Darwin realized that genetic variation made evolution possible, but he could not explain why offspring resembled, but were not identical to their parents. Mendel’s theory of inheritance explained this.