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Biology 15
| Question | Answer |
|---|---|
| genetics | scientific study of heredity and variation |
| heredity | the transmission of traits from one generation to the next |
| variation | demonstrated by the differences in appearance that offspring show from paresnts and sibilings |
| in literal sense children do no | inherit particular physical traits from their parents but inherit genes |
| genes | the units of heredity and are made up of segments of DNA |
| genesrs are passed | to next generation via reproductive cells called gametes |
| locus | specific location on a certain chromosome, each gene has |
| asexual reproduction | single individual passes genes to its offspring without fusion of gametes |
| clone | group of genetically identical individuals from same parent |
| sexual reproduction | 2 parents give rise to offspring that have unique combinations of genes inherited from 2 parents |
| life cycle | generation to generation sequence of stages in the reproduction history of an organism |
| humans somatic cells have | 23 pairs of chromosomes |
| karytotype | an ordered display of the pairs of chromsomes from a cell |
| homologous chromosomes (homologs) | 2 chromosomes in each pair |
| chromosomes in a homologous pair | are the same length and shape and carry genes controlling the same inherited characters |
| sex chromosomes | determine sex of the idvidiual and are called X and Y |
| females have | a homologous pair of X chromosomes |
| males have | one X and one Y chromosome |
| autosomes | the remaining 22 pairs of chromosomes |
| each pair of homologous chromsomes includes | one chromosome from each parent |
| number of chromosomes | 46 chromomes in a human somatic cells- two sets of 23, one from mom and one from dad |
| diploid cells | (2n) has two sets of chromosomes |
| for humans, diploid number is | 46 (2n=46) |
| when dna synthesis has occurred in a cell | each chromosomes is replicated and consists of 2 indentical sister chromatids |
| haploid | (n) a gamete which contains a single set of chromosomes |
| humans haploid number | 23 n=23 |
| eat set of 23 consists of | 22 auntosomes and a single sex chromsome |
| ovum | unferitilized egg with the sex chromosome of X |
| a sperm cell | sex chromosome is X or Y |
| fertilization | the union of gametes (sperm and egg) |
| zygote | fertilized egg which has one set of chromosomes from each parent |
| zygote produces | somatic cells by mitosis and develops into an adult |
| at sexual maturity | the ovaries and testes produce haploid gametes |
| gametes are the only types of cells | produced by meiosis |
| meiosis results in | one set of chromsomes in each gamete |
| fertilization and meiosis | altnerate in sexual life cycles to maintain chromosome number which is common to all organisms that reproduce sexually |
| the 2 main types of sexual life cycles differ in | timing of meiosis and fertilization |
| gametes are the only | haploid cells in anmials and produce by meiosis and undergo no further celldivision before fertilization |
| gametes fuse | to form a diploid zygote that dividies by mitosis and develop into a multicellular organsims |
| alnternation of generations | exhibited by plants and some algae and is a life cycle including both a diploid and haploid multicellular stage |
| sporophyte | a diploid organism which makes haploid spores by meiosis |
| gametophyte | a haploid orgnaims which each spore grows in to by mitosis |
| a gametophyte makes | haploid gametes by mitosis |
| fertilization of gametes in a plant | result in a diploid sporophyte |
| in most fungi and some protist | the only diploid stage is the single celled zygot, there is no multicellular diploid stage |
| the zygote produces | haploid cells by meiosis |
| haploid cells | grow by mitosis into a haploid multicellular organism and produces gametes by mitosis |
| depending on the type of life cycle | either haploid or diploid cells can divide by mitosis but only diploid cells can undergo meiosis |
| in all three life cyccles | halving and doubling of chromosomes contributes to genetic variation in offspring |
| like mitosis, meiosis | is preceded by the replication of chromosomes |
| meiosis takes place in | 2 sets of cell divisions, meiosis I and meiosis II |
| the two cell divisions of meiosis result in | 4 daughter cells rather than two daughter cells in mitosis and each daughter cell has only half as many chromosomes as the parent |
| after chromosomes duplicate | meisosi I and meiosis II follows |
| meiosis I | reductional division, homologs pair up and separate resulting in two haploid daughter cells with replicated chromosomes |
| meiosis II | equaitonal division, sister chromatids sepearate |
| result of meiosis I and II | four haploid daughter cells with unreplicated chromosomes |
| meiosis I is preceded by | interphase, when the chromosomes are duplicated to form sister chromatids |
| sister chromatids are | genetically identical and joined at the centromere |
| centrosome | replicated to form two centrosomes |
| division in meiosis I occurs | in 4 phases, prophase I, metaphase I, anaphase I, and Telophase I & cytokinesis |
| Prophase I | typically occupies mote that 90% of the time required for meiosis, chromosomes begin to condense, homologous chromosomes loosely pair up in synpasis aligned gene by gene |
| crossing over (Prophase I) | nonsister chromatids exchange DNA segments |
| each pair of chromsomes forms a (Prophase I) | tetrad (group of 4 chromosomes) |
| each tetrad (Prophase I) | has one or more chiasmata (x shaped regions where crossing over occurred) |
| Metaphase I | tetrads line up at metaphase plate with on chromosome facing each pole |
| microtubules (metaphase I) | from one pole are attached to kinetochore of one chromosome of each tetrad and from the other pole are attached to the kinetochore of the other chromosome |
| anaphase I | pairs of homologous chromosmes separate, one chromosome moves toward each pole guided by the spindle apparatus and siter chromatids remain attached at the centromere and move as one toward pole |
| telophase I | each half of the cell has a haploid set of chromosomes, each with 2 sister chromatids |
| cytokinesis | occurs simultaneously forming 2 haploid daughter cells |
| animal cells vs plant cells | animal cells: cleavage furrow forms plant cells: cell plate forms |
| at the end of meiosis I and beginning of meiosis II | no chromosomes replicate because the chromsomes are already replicated |
| division in meiosis II occurs in | 4 phases, prophase II, metaphase II, anaphase II, telophase II and cytokinesis |
| prophase II | spindle apparatus forms then chromsomes composed of 2 chromatids move toward the metaphase plate |
| metaphase II | sister chromatids are arranged at the metaphase plate, the kinetochores of sister chromatids attach to microtubules extending from opposite poles |
| anaphase II | the sister chromatids separate and move toward opposite poles as individual chromosomes |
| telophase II | the chromsomes arrive at opposite poles and nuclei forms and chromosomes begin to descend |
| cytokinesis | separates the cytoplasm |
| at the end of meiosis | there are four daughter cells, each with a haploid set of unreplicated chromsomes and are genetically distinct from the others daughters and parent cells |
| mitosis conserves | the number of chromosome setse producing cells that are genetically identical to the parent cell |
| meiosis reduced | number of chromosomes sets from two (diploid) to one (haploid)producing cells that differ genetically from each other and from the parent cell |
| the 3 events that are unique to meiosis | all occur in meiosis I |
| 1st event that are unique to meiosis | synapsis and crossing over in prophase I: homologougenetic infos chromsomse physically connect and exchange |
| 2nd event that are unique to meiosis | at the metaphase plate, there are paired homologous chromosomes( tetrads) instead of individiaul replicated chromosomes |
| 3rd event that are unique to meiosis | at anaphase I, it is homologous chromsomes instead of sister chromatids that separate |
| sister chromatid cohesion allows | sister chromatids of a single chromosome to stay together through meiosis I |
| cohesins | protein complexes which are responsible for cohesion of sister chromatids |
| in mitosis cohesins are | cleaved at the end of metaphase |
| in meiosis cohesins are | cleaved along the chromosome arm in anaphase I (separation of homologs) at the centromeres in anaphase II (separation of sister chromatids) |
| mutations | changes in an organisms dna, the orginal source of genetic diversity |
| alleles | different version of genes created by mutations |
| genetic variation | produced by reshuffling of alleles during sexual reproduction |
| what is responsible for most of variations that arises in each generation | behavior of chromsomes during meiosis and fretilization |
| 3 mechanisms that contribute to genetic variation | independent assortment of chromosomes , crossing over, and random fertilization |
| homolgous pairs of chromsomes | orient randomly at metaphase I of meiosis |
| in independent assortment | each pair of chromosomes sort material and paternal homologs into daughter cells independently of the other pairs |
| number of combinations possible when chromsomes assort independenlty | into gametes is 2^n where n is the haploid number |
| for humans there are more than | 8 million 2^23 possible combinations of chromosomes |
| recombinant chromsomes | combination of dna inherited from each parent which is produced by crossing over |
| crossing over begins | very early in prophase I as homologous chromsomes pair up gene by gene |
| during crossing over | homologous portions of 2 nonsister chromatids trade places |
| crossing over contributes to | genetic variation by combining DNA from 2 parents into a single chromosome |
| random fertilization adds to | genetic variation because any sperm can fuse with any ovum (unfertilized egg) |
| fusion of 2 gametes | each with 8.4 million possible chromosome combinations from independent assortment- produces a zygote with any of about 70 trillion diploid combinations |
| crossing over adds | even more vatiation |
| each zygote has | a unique genetic identity |
| natural selection | results in the accumulation of genetic variations favored by the environment |
| sexual reproduction contributes to | contributes to the genetic vaiation in a population which originates from mutations |
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