Exam II Lectures and Text Pages I. Cell Cycles Mitosis (218 – 228) Meiosis (238 – 249) II. Mendelian Genetics III. Chromosomal Genetics IV. Molecular Genetics Replication Transcription and Translation V. Microbial Models VI. DNA Technology

The Meiotic Cell Cycle A reduction division Allows for sexual reproduction Two parents Creates genetic variation

Hereditary Similarity and Variation Living organisms Are distinguished by their ability to reproduce their own kind 100 µm Figure 12.2 A Figure 13.2 Parent Bud 0.5 mm Figure 13.1

Reproduction and Genetic Variation Asexual reproduction produces genetic clones Requires only mitosis Only one parent Sexual reproduction produces offspring of the same species as the parents, but with genetic variation Requires meiotic cell division at some time in the lifecycle Two parents

Terms Heredity Variation Genetics Is the transmission of traits from one generation to the next Variation Inherited differences among individuals of the same species. Shows that offspring differ somewhat in appearance from parents and siblings Figure 13.1 Genetics Is the scientific study of heredity and hereditary variation

Inheritance of Genes Genes Are the units of heredity Are specific linear sequences of nucleotides on a DNA molecule Are packaged on and transmitted by chromosomes

Inheritance of Genes Each gene in an organism’s DNA We inherit Has a specific locus on a certain chromosome We inherit One set of chromosomes from our mother and one set from our father Most genes program the cell to make a specific protein; the action of proteins produce inherited traits.

Comparison of Asexual and Sexual Reproduction In asexual reproduction One parent produces genetically identical offspring by mitosis Figure 13.2 Parent Bud 0.5 mm

Comparison of Asexual and Sexual Reproduction In sexual reproduction Two parents give rise to offspring that have unique combinations of genes inherited from the two parents Figure 13.1

Life Cycles Fertilization and meiosis alternate in sexual life cycles A life cycle Sequence of stages from conception to reproduction in an organism’s life.

Sets of Chromosomes in Human Cells In humans Each somatic cell has 46 chromosomes, made up of two sets One set of chromosomes comes from each parent (in the gamete)

Karyotyping A karyotype Is an ordered (standard sequence), visual representation of the chromosomes in a somatic cell 5 µm Pair of homologous chromosomes Centromere Sister chromatids Figure 13.3

Homologous Chromosomes (Homologues) Are the two chromosomes composing a pair Have the same characteristics (size, centromere, staining pattern) Have the same loci at the same locations on the chromosome Are inherited as one member of each pair from each parent

Chromosomes Autosome: A chromosome that is not a sex chromosome. Sex chromosomes Are distinct from each other in their characteristics Are represented as X and Y Determine the sex of the individual, XX being female, XY being male

Sets of Chromosomes A haploid cell Has one set of chromosomes A human gamete is haploid and has 23 chromosomes (n = 23) A diploid cell Has two haploid sets of each of its chromosomes In a human has 46 chromosomes (2n = 46)

Human Life Cycle At sexual maturity During fertilization The zygote Ovaries and testes produce haploid gametes by meiosis During fertilization Gametes fuse, forming a diploid zygote The zygote Develops into an adult by mitotic cell division Figure 13.5 Key Haploid (n) Diploid (2n) Haploid gametes (n = 23) Ovum (n) Sperm Cell (n) MEIOSIS FERTILIZATION Ovary Testis Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46)

The Variety of Sexual Life Cycles The three main types of sexual life cycles differ in the timing of meiosis and fertilization 1. Diploid adult produces haploid gametes by meiosis, all other stages are diploid 2. Two adult life stages, one diploid (produce spores by meiosis) and one haploid (produce gametes by mitosis) 3. Haploid adult produces gametes by mitosis, diploid zygote produces haploid spores by meiosis. All stages except zygote are haploid

Animal Life Cycle Meiosis occurs during gamete formation Gametes are the only haploid cells Gametes Figure 13.6 A Diploid multicellular organism Key MEIOSIS FERTILIZATION n 2n Zygote Haploid Mitosis (a) Animals

Plants and Some Algae Life Cycle Exhibit an alternation of generations The life cycle includes both diploid and haploid multicellular adult stages MEIOSIS FERTILIZATION n 2n Haploid multicellular organism (gametophyte) Mitosis Spores Gametes Zygote Diploid multicellular organism (sporophyte) (b) Plants and some algae Figure 13.6 B

Most Fungi and Some Protists Life Cycle Meiosis produces haploid cells that give rise to a haploid multicellular adult organism The haploid adult carries out mitosis, producing cells that will become gametes Zygote is only diploid stage MEIOSIS FERTILIZATION n 2n Haploid multicellular organism Mitosis Gametes Zygote (c) Most fungi and some protists Figure 13.6 C

Chromosome Duplication Precedes either type of cell division All the chromosomes are duplicated and thus each consists of two identical sister chromatids Figure 13.4 Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of chromosomes (n = 3) Two sister chromatids of one replicated chromosome Centromere Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set)

Meiosis – A Reduction Division Meiosis reduces the number of chromosome sets from diploid to haploid Meiosis Takes place in two divisions, meiosis I and meiosis II

Stages of the Meiotic Cell Cycle Interphase Chromosomes and centrosomes replicate Meiosis I Separates each homologous pair and reduces the number of chromosomes from diploid to haploid Meiosis II Separates sister chromatids and produces four haploid daughter cells Figure 13.7 Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes 1 2 Homologous separate Haploid cells with replicated chromosomes Sister chromatids Haploid cells with unreplicated chromosomes Meiosis I Meiosis II

Interphase and Meiosis I Synapsis and crossing over occur. Pairs of homologous chromosomes are separated Centrosomes (with centriole pairs) Sister chromatids Chiasmata Spindle Tetrad Nuclear envelope Chromatin Centromere (with kinetochore) Microtubule attached to kinetochore Tertads line up Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Pairs of homologous chromosomes split up Chromosomes duplicate Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example INTERPHASE MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I Figure 13.8

Telophase I and Cytokinesis Meiosis I is the reduction division – yields two haploid cells TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND MEIOSIS II: Separates sister chromatids Cleavage furrow Sister chromatids separate Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes Two haploid cells form; chromosomes are still double Figure 13.8

Interkinesis In some species: After telophase I and cytokinesis, nuclear membranes and nucleoli reappear, and the cell enters a period of interkinesis before meiosis II. In other species, the daughter cells immediately prepare for meiosis II. With or without interkinesis, no DNA replication occurs.

Meiosis II Meiosis II separates sister chromatids (similar to mitosis) Figure 13.8