Crossing over contributes to genetic variation by

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Chapter 19 / Exercise 14
Microeconomics
Arnold
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Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosomeDiagram text page 277oRandom fertilizationAdds to genetic variation (any sperm can fuse with any ovum)Each gamete has 8.4 million possible chromosome combinations from independent assortmentFusion of two gametes produces a zygote with any of about 70 trillion diploid combinations Crossing over adds even more variation as each zygote has a unique genetic identityNatural selection results in the accumulation of genetic variations favoured by environmentSexual reproduction contributes to genetic variation in population, originates form mutations40.Compare and contrast meiosis and mitosis.Diagram text page 275
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Chapter 19 / Exercise 14
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Arnold
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21Meiosis Mitosis Definition oA type of sexual reproduction in which the number of chromosomes are reduced byhalf through the separation of homologous chromosomes, producing two haploid cellsoA process of asexual reproduction in which a cell divides in two producing a replica, with an equal number of chromosomes in each resulting diploid cellFunction oGenetic diversity through sexual reproduction oCellular reproductionoGrowthoDevelopmentoRepairOccurs inoHumans oAnimalsoPlantsoFungi oAll organismsGenetically oDifferent oIdentical Crossing over oYes, mixing of chromosomesoNo, cannot occurPairing ofhomologues oYes oNo Number ofdivisionso2o1Number daughtercells producedo4 haploid cellso2 diploid cellsChromosomenumber oReduced by halfoRemains the sameSteps involvedoMeiosis 1 (PMAT 1)oMeiosis 2 (PMAT 2)oCytokinesis oInterphase (G1, S, 62)oM phase, mitosis oCytokinesis Karyokenesis oOccurs interphase 1oOccurs in interphaseCytokinesis oOccurs telophase 1 and 2oOccurs in telophaseCentromeres splitoSeparate in anaphase 2oSplit during anaphaseCreates oGametes (sex cells sperm and eggs)oSomatic cells (anything other than sex cells)Discovered byoOscar HertwigoWalter Fleming41.Compare and contrast asexual and sexual reproduction.
22In sexual reproduction, two parents give rise to offspring having unique combinations of genes inherited from bothRandom mutations in DNA are the ultimate source of variability for both sexual and asexual reproduction. BUT mutations are relatively rare. Thus diversity is amplified through various mechanisms that shuffle existing mutations into different combinations. Without genetic recombination, reproduction would be asexual and offspring would be identical clones of their one parentAsexual reproduction: oTypes include binary fission, budding and regeneration/segmentation Advantages Disadvantages oEnergy isn’t wasted on producing gametesoEnergy isn’t wasted on finding/securing a mateoDon’t have to move (sessile animals)oGenetic uniformity of offspring (stable environment)o

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