Chapter3 Heredity Influences on Develop

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1、HeredityInfluencesonDevelopmentChapter3Dr.PelaezPrinciplesofHeredityTransmissionTheGeneticCodeConceptionisthemomentoffertilization,whenaspermpenetratesanovum,formingazygote.Thezygotecontains46chromosomes,consistingofthousandsofchemicalsegments,orgenes.Genesarehereditaryblueprintsfordevel

2、opmentthatarepassedonunchangedfromgenerationtogeneration.Chromosomescomeinmatchingpairs.(23chromosomesfromeachparent.)GrowthoftheZygoteandProductionofBodyCellsThezygotemovesthroughthefallopiantubetowardtheuterus,andbeginstheprocessofmitosis.Thezygotefirstdivideinto2cells,then2become4,4be

3、come8,8become16,etc.Beforeeachdivision,thezygoteduplicatesits46chromosomes.Germ(orSex)CellsThegermcellsarethesexcellsofthezygote.Thegermcells’functionistoproducegametes,whichareeithersperminmalesorovainfemales.Meiosisoccurswhenthemalegermcellinthetestesproducesspermandwhenthefemalegermce

4、llintheovariesproducesova.Oftencross-overtakesplace.Thisiswhenthereisanexchangeofgeneticmaterial.MultipleBirthsMultiplebirthsoccurwhenthearetwopeoplewhoshareagenotype.Whenthezygotebeginstheprocessofmitosisitmaybegintosplitintoidenticalcells.Atthismomenttwoindividualshavebeenformed.Thisis

5、anexampleofmonozygotictwins.Dizygotictwinsaremorecommon.Thesearetwinsthatresultwhenamotherreleasestwoovaatthesamemomentandeachisfertilizedbyadifferentsperm.The23rdpairofchromosomesThesexofthezygoteisdeterminedbythe23rdpairofchromosomes.Forafemalesex,bothofthesesexchromosomesareanXchromos

6、ome.Foramalesex,the23rdpairconsistsofoneXchromosomeandoneYchromosome.Thepurposeofourgenes…..Ourgenesareresponsiblefortheconstructionofourenzymesandotherproteins.Thesegenesareessentialinordertoformnewcellsandtheirspecificfunctions.Othergenesareaccountableforregulatingthepaceofdevelopment.

7、Howaregenesexpressed?SimpleDominant-RecessiveInheritanceAlleles:humancharacteristicsthatareinfluencedbyonepairofgenes(onefromthemother,onefromthefather).1)Dominant-recessive:apatternofinheritanceinwhichonealleledominatesanothersothatitsphenotypeisonlyexpressed2)Dominant:a