BIOL 1441 1st Edition Lecture 22 Outline of Last Lecture I. Cyclins and Cyclin-dependent kinasesII. Cell growth-cancer genesIII. MeiosisIV. Gamete productionV. nondisjunctionOutline of Current Lecture I. MeiosisII. Stages of Meiosis IIII. Stages of Meiosis IIIV. Meiosis and diversityV. HeredityVI. Chromosomes-somatic cells/gametesVII. TwinsVIII. Asexual/sexual reproductionIX. Genetic variationCurrent LectureI. Meiosisa. Gametes go through cell cycle like mitosisi. Meiosis is preceded by the replication of chromosomesb. Meiosis- two sets of cell divisionsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Meiosis I & meiosis IIii. Mitosis- one cell divisionc. Meiosis- results in 4 nonidentical daughter cellsi. Mitosis- results in 2 identical daughter cellsd. Diploid (2n)- cells that contain 46 chromosomesi. Somatic cellse. Haploid (n)- cells that contain 23 chromosomesi. Gametes (sex cells)II. Stages of Meiosis Ia. Meiosis I- homologous chromosomes separate (chromosome pairs, not sister chromatids)i. 92 ® 46b. Results in two daughter cells with replicated chromosomes (sister chromatids) i. Diploid, 46 chromosomesc. Homologous Chromosomes: pairs of chromosomes with same genetic material but not identicali. Pair of individual chromosomes- one from mom, one from dad. NOT sister chromatidsd. Division in meiosis I occurs in four phases:i. Prophase I1. Chromosomes condensed2. Spindle formation, nuclear envelope breaking down3. Genetic recombination4. Synapsis- homologous chromosomes align gene by gene5. Crossing over- chromosomes break apart, non-sister chromatids exchange DNA segmentsa. Enzyme snips in half and fuses DNA opposite of each otherb. Only the 2 homologs in the center cross over6. Chiasmata- criss-crossed regions of DNA, holding homologous chromosomes together7. 90% of the time8. Tetrad- group of four sister chromatids9. Each tetrad has one or more chiasmata10. Late prophase- microtubules attach to kinetochores of the chromosomesii. Metaphase I1. Tetrads line up on metaphase plate, with one chromosome facing each pole2. Genetic recombination place 2iii. Anaphase I1. Chromosome moves toward opposite poles, guided by the spindleapparatus2. Sister chromatids remain attached at the centromere & move as one unit toward the pole3. Pairs of homologous chromosomes separateiv. Telophase I & Cytokinesis1. Each cell contains sister chromatids2. Cytokinesis usually occurs simultaneously3. Animals- cleavage furrow forms4. Plants- cell plate formsIII. Stages of Meiosis IIa. Separation of sister chromatidsb. 4 phasesi. Prophase II1. Spindle apparatus forms2. Late prophase II chromosomes (each still composed of two chromatids) move toward the metaphase plateii. Metaphase II1. Kinetochores of sister chromatids attach to microtubules extending from opposite poles2. Sister chromatids line up on metaphase platea. No longer genetically identicaliii. Anaphase II1. Sister chromatids separate2. Sister chromatids of each chromosome now move as individual chromosomes toward opposite polesiv. Telophase II & Cytokinesis1. Nuclei form2. Chromosomes begin decondensing3. Cytokinesis separates the cytoplasm4. 4 n (haploid) daughter cell, nonidenticalIV. Meiosis & Diversitya. Genetic diversity is essential for lifeb. Essential for survival of speciesc. Species or ecosystem- more diversity, healthier population or systemd. Challenged with environmental pressuresi. Different genes selected forii. Natural selection- favorable genes you will most likely survive to pass thatgenetic information onV. Hereditary Similarity & Variationa. Heredity- transmission of traits from one generation to the nextb. Genetics- scientific study of heredity and variationc. Genetic information is transferred by DNAd. Genes- segments of DNA, units of heredityi. Code for a protein, physical trait (eye color)e. Inheritance of Genesi. Each gene has a specific locus (location) on a certain chromosomeii. One chromosome- thousands of genes on itf. Chromosomes in Human Cellsi. Chromosomes differ in size, centromere position, stain differentlyii. Karyotype- ordered display of the pairs of chromosomes from a cell 1. 23 pairs in somatic cells (46 total)VI. Chromosomes- Somatic Cella. Autosomes- 22 pairs of chromosomes that do not determine sexb. 1 pair of sex chromosomes- X and Yi. Females- XXii. Males- XYc. Chromosomes- Gametesi. Haploid cells, n = 23ii. 22 autosomes and a single sex chromosomeiii. Egg (ovum)- sex chromosome is Xiv. Sperm cell- the sex chromosome X or YVII. Twinsa. Identical- monozygotic i. 1 eggii. Divides into 2 separate embryosiii. Random not hereditaryb. Fraternal- dizygotic i. 2 separate eggsii. Genetic componentiii. Yoruba, Nigeriac. Monozygotic twins split into 2 zygotes very early in the pregnancyd. Timing of this separation determines the chorionicity and amniocity (the number of sacs) of the pregnancy.i. Dichorionic twins divide ~first 4 daysii. Monoamnionic twins divide after 1st week.e. In very rare cases, twins become conjoined twins (if separation happens too late)VIII. Asexual & Sexual Reproduction a. Asexual reproduction- 1 parent produces genetically identical offspring by mitosisb. Sexual reproduction- 2 parents give rise to offspring that have unique combinations of inherited genesIX. Genetic Variationa. Mutations (changes in an organism’s DNA)- original source of genetic diversityb. Mutations create different versions of genesc. During sexual reproduction, several occurrences create genetic variationi. Independent assortment of chromosomesii. Crossing overiii. Random fertilizationd. Independent Assortment of Chromosomesi. Homologous pairs of chromosomes randomly line up at metaphase I of meiosisii. Each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairse. Crossing Overi. Produces recombinant chromosomes1. Combine genes inherited from each parentii. Begins very early in prophase I, as homologous chromosomes pair up gene by geneiii. Homologous portions of two nonsister chromatids trade placesiv. Contributes to genetic variation by combining DNA from two parents into a single chromosomef. Random Fertilizationi. Any sperm can fuse with any egg1. Remember meiosis- produce 4 nonidentical haploid gametes (due to independent assortment & crossing over)ii. Fusion of gametes produces a zygote with any of about 64 trillion diploid