"Biology"-Campbell, Reece
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| 489318414 | Heredity | Or inheritance. The transmission of traits from one generation to the next. | |
| 489318415 | Genetics | The study of heredity and hereditary variation. | |
| 489318416 | Genes | Hereditary units with coded information endowed to offspring by their parents. All of our genes constitute our genome. Segments of DNA. Inherited information is passed on in the form of each gene's specific sequence of nucleotides. Most program cells to synthesize specific enzymes and other proteins whose cumulative action produces an organism's inherited traits. | |
| 489318417 | Gametes | The reproductive cells in animals and plants. The vehicles that transmit genes from one generation to the next. | |
| 489318418 | Locus | A genes specific location along the length of a chromosome. | |
| 489318419 | Asexual Reproduction | A single individual is the sole parent and passes copies of all its genes to its offspring--offspring are exact copies of themselves. Gives rise to a clone. Genetic differences can arise as a result of mutations | |
| 489318420 | Clone | A group of genetically identical individuals. | |
| 489318421 | Sexual Reproduction | In this process, two parents give rise to offspring that have unique combinations of genes inherited from the two parents. Offspring vary genetically from their siblings and parents. | |
| 489318422 | Somatic Cell | Any cell other than a gamete. In humans, each cell has 46 chromosomes. | |
| 489318423 | Karyotype | The number and appearance of chromosomes in the nucleus of a eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism | |
| 489318424 | Homologous Chromosomes | Or homologues. Chromosome pairs of approximately the same length, centromere position, and staining pattern, with genes for the same characteristics at corresponding loci. One homologous chromosome is inherited from the mother and the other from the father. The two distinct chromosomes referred to as X and Y are an important exception to the general pattern of homologous chromosomes in human somatic cells: females have a homologous pair of X chromosomes while males have one X and one Y. Only parts of the X and Y are homologous. | |
| 489318425 | Sex Chromosomes | The X and Y chromosomes. The two distinct chromosomes referred to as X and Y are an important exception to the general pattern of homologous chromosomes in human somatic cells: females have a homologous pair of X chromosomes while males have one X and one Y. Only parts of the X and Y are homologous. | |
| 489318426 | Autosomes | All the chromosomes except for the sex chromosomes (X and Y). | |
| 489318427 | Diploid Cell | Any cell with two chromosome sets. | |
| 489318428 | Haploid Cells | Cells that contain a single set of chromosomes. Gametes are these. | |
| 489318429 | Fertilization | The union of gametes; when a haploid sperm cell from a father fuses with a haploid ovum from the mother. Results in a zygote. | |
| 489318430 | Zygote | The fertilized egg that results from two haploid gametes fusing. Is diploid since it contains two haploid sets of chromosomes bearing genes representing the maternal and paternal family lines. | |
| 489318431 | Meiosis | Type of cell division that reduces the number of sets of chromosomes from two to one in the gametes, compensating for the doubling that occurs at fertilization. In mammals, it only occurs in the ovaries or testes. | |
| 489318432 | Alternation of Generations | A second type of life cycle that is exhibited by plants and some species of algae. Includes both diploid and haploid multicellular stages. The multicellular diploid stage is called the sporophyte and the multicellular haploid stage is called the gametophyte. (i.e. The sporophyte produces a gametophyte as its offspring, and the gametophyte produces the next sporophyte generation. | |
| 489318433 | Sporophyte | The multicellular diploid stage of the alternation of generations life cycle seen in plants and some species of algae. Meiosis in the sporophyte produces haploid cells called spores. | |
| 489318434 | Gametophyte | The multicellular haploid stage of the alternation of generations life cycle seen in plants and some species of algae. Makes gametes by mitosis. Fertilization among haploid gametes results in a diploid zygote, which develops into the next sporophyte generation. | |
| 489318435 | Spores | The haploid cells produced by meiosis from sporophytes. Unlike a gamete, a spore gives rise to a multicellular individual without fusing with another cells. Divides mitotically to generate a multicellular haploid called a gametophyte. | |
| 489318436 | Life Cycle of Fungi (and some protists) | Undergo a special type of life cycle. After gametes fuse and form a diploid zygote, meiosis occurs without a diploid offspring developing. Meiosis produces not gametes but haploid cells that then divide by mitosis and give rise to a haploid multicellular adult organism. Subsequently, the haploid organism carries out mitosis, producing the cells that develop into gametes. The only diploid stage in these species is the single-celled zygote. | |
| 489318437 | Stages of Meiosis | Made up of meiosis I (separating of homologous chromosomes) which includes prophase I, metaphase I, anaphase I, telophase I and cytokinesis and meiosis II (separation of sister chromatids) which includes prophase II, metaphase II, anaphase II, telophase II and cytokinesis. No chromosome replication occurs between the end of meiosis I and the beginning of meiosis II, as the chromosomes are already replicated. | |
| 489318438 | Prophase I | First stage of meiosis and meiosis I. Usually occupies more than 90% of the time required for meiosis. Chromosomes begin to condense. Homologous chromosomes loosely pair along their lengths, precisely aligned gene by gene. In crossing over, the DNA molecules in nonsister chromatids break at corresponding places and then rejoin to the other's DNA. In synapsis, a protein structure called the synaptonemal complex forms between homologues, holding them tightly together along their lengths. The synaptonemal complex disassembles in late prophase, and each chromosome pair become visible in the microscope as a tetrad, a group of 4 chromosomes. Each tetrad has one or more chiasmata that hold the homologues of each pair facing each pole. Both chromatids of a homologue are attached to kinetochore microtubules from one pole' those of the other homologue are attached to microtubules from the opposite pole. | |
| 489318439 | Metaphase I | Second stage of meiosis and meiosis I. The pairs of homologous chromosomes, in the form of tetrads, are now arranged on the metaphase plate, with one chromosome of each pair facing each pole. Both chromatids of a homologue are attached to kinetochore microtubules from one pole; those of the other homologue are attached to microtubules from the opposite pole. | |
| 489318440 | Anaphase I | Third stage of meiosis and meiosis I. The chromosomes move towards the poles, guided by the spindle apparatus. Sister chromatids remain attached at the centromere and move as a single unit toward the same pole. Homologous chromosomes, each composed of two sister chromatids, move toward opposite poles. | |
| 489318441 | Telophase I | Fourth stage of meiosis and meiosis I. At the beginning, each half of the cell has a complete haploid set of chromosomes, but each chromosome is still composed of two sister chromatids. | |
| 489318442 | Cytokinesis in Meiosis I | Usually occurs simultaneously with telophase I, forming two haploid daughter cells. In animal cells, a cleavage furrow forms and in plant cells a cell plate forms. In some but not all species, the chromosomes decondense and the nuclear envelope and nucleoli re-form. | |
| 489318443 | Prophase II | First stage of meiosis II. A spindle apparatus forms. In late prophase II, chromosomes, each still composed of two chromatids, move toward the metaphase II plate. | |
| 489318444 | Metaphase II | Second stage of meiosis II. The chromosomes are positioned on the metaphase plate as in mitosis. Because of crossing over in meiosis I, the two sister chromatids of each chromosome are not genetically identical. The kinetochores of sister chromatids are attached to microtubules extending from opposite poles. | |
| 489318445 | Anaphase II | Third stage of meiosis II. The centrosomes of each chromosome finally separate, and the sister chromatids come apart. The sister chromatids of each chromosome move as two individual chromosomes toward opposite poles. | |
| 489318446 | Telophase II | Fourth stage of meiosis II. Nuclei form, the chromosome begin decondensing, and cytokinesis begins. | |
| 489318447 | Cytokinesis in Meiosis II | The meiotic division of one parent cell produces four daughter cells, each with a haploid set of chromosomes. Each of the four daughter cells is genetically distinct from the other daughter cells and from the parent cell. | |
| 489318448 | Synapsis | The process that occurs during prophase I in which duplicated homologous chromosomes line up and become physically connected along their lengths by a zipper-like protein structure, the synaptonemal complex. | |
| 489318449 | Synaptonemal Complex | The zipper-like protein structure that physically connects duplicated homologous chromosomes along their lengths during prophase I in a process called synapsis. | |
| 489318450 | Crossing Over | Genetic rearrangement between nonsister chromatids which occurs during prophase I. Each gene on one homologous chromosome is aligned precisely with the corresponding gene on the other homologue. In humans, an average of 1-3 crossover events occur per chromosome pair, depending on the size of the chromosomes and the positions of their centromeres. | |
| 489318451 | Tetrad | The synaptonemal complex made up of the four chromatids of a homologous pair. Each one normally contains at least 1 X-shaped region called a chiasma. | |
| 489318452 | Chiasma | The X-shaped region that is a physical manifestation of crossing over in a tetrad. At least one in every tetrad. | |
| 489318453 | Reductional Division | What meiosis I is called because it halves the number of chromosome sets per cell--a reduction from two sets to one set (i.e. diploid state to haploid state). | |
| 489318454 | Three Mechanisms that Contribute to the Genetic Variation Arising from Sexual Reproduction | 1. Independent assortment of chromosomes--at metaphase I, the homologous pairs can situate themselves in different orientations. 2. Crossing over. 3. Random fertilization. | |
| 489318455 | Independent Assortment | Each homologous pair of chromosomes is positioned independently of the other pairs at metaphase I so the first meiotic division results in each pair sorting its maternal and paternal homologues into daughter cells independently of every other pair. The number of possible combinations when chromosomes sort independently during meiosis is 2^n, where n is the haploid number of the organism. | |
| 489318456 | Recombinant Chromosomes | Produced by crossing over. Individual chromosomes that carry genes derived from two different parents. |
