BIOLOGY - CLUTCH CH.13 - MEIOSIS.

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2 CONCEPT: SEXUAL REPRODUCTION Meiosis is a special type of cell division that occurs as part of the sexual life cycle of eukaryotes Sexual reproduction parents donate a unique mixture of their DNA to offspring Heredity the transmission of genetic traits from parent to offspring Assexual reproduction single parent gives rise to offspring with same genetic makeup Allele a version gene e.g. blood type A, B, O Gene locus (loci plural) the location of a gene on a chromosome Homologous chromosomes chromosomes that the same genes at the same loci Page 2

3 CONCEPT: SEXUAL REPRODUCTION A karyotype is a picture of a person s chromosomes. Humans have 44 autosomes, and 2 sex chromosomes Haploid only one copy of each chromosome Diploid two copies of each chromosome Somatic cells diploid cells of the body of an organism Germ cells produce gametes haploid cells that transfer genetic material in sexual reproduction Fertilization is when gametes fuse and create a zygote, the first cell of an organism! Page 3

4 CONCEPT: SEXUAL REPRODUCTION Alteration of generations - unlike animals, plant life cycles alter between multicellular haploid, and diploid forms. Most fungi exhibit a life cycle in which the only diploid stage is the zygote. The Paradox of Sex Even though sexual reproduction has its disadvantages, with it comes genetic variation, which can be advantageous. Page 4

5 PRACTICE: 1. Mitosis is nuclear division that yields cells, while meiosis is nuclear division that produces cells. a. hapoid diploid c. gametic somatic b. diploid haploid d. gametic haploid 2. Multicellular organisms are made of diploid cells, except for their gametes. a. True b. False Page 5

6 CONCEPT: MEIOSIS Meiosis occurs in two stages: Meiosis I Reductional division Meiosis II Equational division Page 6

7 CONCEPT: MEIOSIS Prophase I: like prophase of mitosis, but the chromosomes behave differently Synapsis homologs pair allowing for exchange of chromosome pieces Tetrads the two pairs of sister chromatids of homologous chromosomes Synaptomal complex protein complex that holds the homologs together Crossing over the exchange of pieces of chromosomes that occurs in prophase I Chiasmata the point where two homologous, non-sister chromosomes connect Page 7

8 CONCEPT: MEIOSIS Metaphase I: Homologs align on metaphase plate, and each homolog pair attaches to microtubules from opposite poles The microtubules from one pole attach to the kinetochore of both sister chromatids Anaphase I: Homologs separate and move to opposite poles Sister chromatids remain attached Telophase I and Cytokinesis: Each cell is left haploid with one pair of sister chromatids from each pair of homologous chromosomes No chromosome duplication occurs before meiosis II Page 8

9 CONCEPT: MEIOSIS Prophase II: spindle apparatus forms Metaphase II: Sister chromatids align at the metaphase plate (they are not genetically identical) Microtubules from opposite poles attach to the kinetochores of sister chromatids Anaphase II: sister chromatids separate and move to opposite poles Telophase II and Cytokinesis: results in haploid daughter cell Page 9

10 CONCEPT: MEIOSIS Nondisjunction when sister chromatids, or homologs fail to separate during cell division Aneuploidy the wrong number of chromosomes, can be as a result of nondisjunction Genetic Variation: Independent assortment during metaphase I the homologous pairs assort independently of each other Recombination when cross over occurs, genes are swapped between chromosomes Random fertilization which gametes will fuse, is up to chance Page 10

11 PRACTICE: 1. Which phase of the cell cycle is lacking between the two meiotic divisions? a. P phase b. M phase c. S phase d. a full cell cycle 2. A diploid organism has 28 chromosomes. How many chromosomes will the cell have after mitosis but before cytokinesis? a. 7 b. 14 c. 28 d A scientist observes cells undergoing meiosis. At the end of meiosis I, it is noted that the two resulting daughter cells are both haploid. This is because the cells that resulted from meiosis I are but are composed of two sister chromatids that will be pulled apart during, producing haploid gametes. a. diploid metaphase I c. diploid meiosis II b. haploid anaphase I d. haploid meiosis II 4. Why do most genes sort independently? a. their protein products are unrelated traits b. their protein products are related traits c. they are on different chromosomes d. they are different alleles Page 11