BIOL 1406 Chapter 15 Meiosis
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| 427954831 | Genetics | scientific study of heredity and hereditary variation | 0 | |
| 427954832 | Heredity/inheritance | the transmission of traits from one generation to the next | 1 | |
| 427954833 | Hereditary variation | demonstrated by the differences in appearance that offspring show from parents and siblings | 2 | |
| 427954834 | Genes | hereditary units in which parents endow their offspring with coded information; made up of segments of DNA, the polymer that consist of four different nucleotides (A, G, C and T) | 3 | |
| 427954835 | Gametes | Genes are passed to the next generation through reproductive cells (sperm and eggs); contain a single chromosome set (n) | 4 | |
| 427954836 | Chromosomes | except for small amounts of DNA in mitochondria and chloroplasts, the DNA of a eukaryotic cell is packaged as THIS in the nucleus; humans have 46; each consists of a single long, linear DNA molecule elaborately coiled in association with various proteins; represented by the letter n | 5 | |
| 427954837 | Somatic cell | any cell other than a gamete | 6 | |
| 427954838 | Karyotype | chromosomes are arranged in pairs, starting with the longest chromosome, the resulting ordered display | 7 | |
| 427954839 | Homologous chromosomes | two chromosomes in each pair have the same length, centromere position and staining pattern | 8 | |
| 427954840 | Autosomal chromosomes | The 22 pairs of chromosomes that do not determine sex | 9 | |
| 427954841 | Diploid cell | Any cell with two chromosome sets (2n) | 10 | |
| 427954842 | Fertilization | The union of gametes, culminating in the fusion of their nuclei | 11 | |
| 427954843 | Zygote | Fertilized egg; diploid b/c of 2 haploid sets of chromosomes, one set from each parent | 12 | |
| 427954844 | Germ cells | Specialized cells where gametes develop | 13 | |
| 427954845 | Meiosis | reduces the number of chromosome sets from two (diploid=2n) to one (haploid=n), producing 4 haploid daughter cells that differ genetically from each other and from the parent cell. Each haploid daughter cell has a random mix of chromosomes | 14 | |
| 427954846 | Prophase 1 | typically occupies more than 90% of the time required for meiosis; Chromosomes begin to condense; synapsis and crossing over occurs | 15 | |
| 427954847 | Synapsis | homologous chromosomes loosely pair up, aligned gene by gene | 16 | |
| 427954848 | Crossing over | nonsister chromatids exchange DNA segments | 17 | |
| 427954849 | Tetrad/bivalent | group of four sister chromatids | 18 | |
| 427954850 | Chiasmata | X-shaped regions where crossing over occurred; each tetrad usually has one or more | 19 | |
| 427954851 | Prometaphase 1 | The spindle apparatus is complete, and the chromatids are now attached to kinetochore microtubules; Pairs of sister chromatids, one member of each homologous pair, are attached to opposite poles | 20 | |
| 427954852 | Metaphase 1 | the tetrads line up at the metaphase plate, with one replicated chromosome facing each pole Kinetochore microtubules from one pole are attached to the kinetochore of one replicated chromosome of each tetrad Kinetochore microtubules from the other pole are attached to the kinetochore of the other replicated chromosome | 21 | |
| 427954853 | Anaphase 1 | pairs of homologous chromosomes separate; Connections between the bivalents break, but not the connections that hold the sister chromatids together One replicated chromosome moves toward each pole, guided by the spindle apparatus Sister chromatids remain attached at the centromere and move as one unit toward the pole | 22 | |
| 427954854 | Telophase 1 and Cytokinesis | in the beginning, each half of the cell has a haploid set of replicated chromosomes; each chromosome still consists of two sister chromatids Replicated chromosomes have reached their respective poles and decondense and nuclear membranes reform Cytokinesis usually occurs simultaneously, forming two haploid daughter cells | 23 | |
| 427954855 | Meiosis 2 | There is no S phase before The sorting events during are very similar to those of mitosis Sister chromatids are separated during anaphase II, unlike anaphase I | 24 | |
| 427954856 | Prophase 2 | a spindle apparatus forms. There are no tetrads or bivalents. | 25 | |
| 427954857 | Prometaphase 2 | Kinetochore microtubules attach to replicated chromosomes (each still composed of two chromatids) and move them toward the metaphase plate. | 26 | |
| 427954858 | Metaphase 2 | the sister chromatids (replicated chromosomes) are arranged at the metaphase plate. Because of crossing over in meiosis I, the two sister chromatids of each chromosome are no longer genetically identical! The kinetochores of sister chromatids attach to microtubules extending from opposite poles. | 27 | |
| 427954859 | Anaphase 2 | the sister chromatids separate. The sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles. | 28 | |
| 427954860 | Telophase 2 | In telophase II, the chromosomes arrive at opposite poles. Nuclei form, and the chromosomes begin decondensing. Cytokinesis separates the cytoplasm. At the end of meiosis, there are four daughter cells, each with a haploid set of unreplicated chromosomes. Each daughter cell is genetically distinct from the others and from the parent cell. | 29 | |
| 427954861 | Mitosis | conserves the number of chromosome sets, producing 2 daughter cells that are genetically identical to the parent cell | 30 | |
| 427954862 | Alleles | alternate versions of the same gene that occupy the same locus | 31 | |
| 427954863 | 3 things contributing to genetic variation | -Independent assortment of chromosomes -Crossing over -Random fertilization | 32 | |
| 427954864 | Independent Assortment of Chromosomes | -One aspect of sexual reproduction that generates genetic variation is the random orientation of homologous pairs of chromosomes at metaphase of meiosis I. -each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs. -Each pair may orient with either its maternal or paternal homolog closer to a given pole -The number of combinations possible when chromosomes assort independently into gametes is 2n, where n is the haploid number. -For humans (n = 23), so then, there are more than 223 or 8 million possible combinations of chromosomes. | 33 | |
| 427954865 | Crossing over | -produces recombinant chromosomes, individual chromosomes that carry genes (DNA) derived from two different parents. -homologous chromosomes pair up gene by gene and homologous portions of two nonsister chromatids trade places. -contributes to genetic variation by combining DNA from two parents into a single chromosome. | 34 | |
| 427954866 | Random fertilization | -adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg). -The fusion of two gametes (each with 223 or 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about (223 x 223) 70 trillion diploid combinations. -If we factor in the variation brought about by crossing over, then the number of possibilities is truly astronomical | 35 |
